Biology Notes

2012-01-29T17:54:00.000-08:00

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Palaeophysiology of sloths: Why some giant sloths probably evolved from tree-dwelling sloths

The venous return of sloths shares some peculiarities with a few other mammals, many of which are tree dwelling (clinging to branches) or diving (seals and whales). The special circulatory features include a double vena cava and an large internal vertebral vein. In the sloth (Choloepus), the two venae cavae connect with this epidural vertebral vein. The vein is as large in diameter as the spinal cord, which is in fact displaced laterally. All of this is described in the classic work by M. Goffart, "Function and Form in the Sloth" (1971).

In a review paper I published in 1990 (Comp. Biochem. Physiol. Vol. 95A, No. 1, pp. 23-25), I pointed out that a range of mammals which experience a shortage of blood to the limbs share certain unusual vascular features (not only those already mentioned but also features such as vascular bundles - a highly developed form of counter-current heat exchanging arrangement of arteries and veins, of the kind sometimes known as a rete mirabile). The shortage of blood to the limbs can be caused by diving, and diversion of blood to the trunk and away from the limbs, or by prolonged clinging postures, which will also tend to reduce blood supply to the limbs and divert it to trunk.

We cannot observe the circulation in the limbs of extinct giant ground sloths, but we can determine that they shared the internal vertebral veins found in living sloths (Goffart writes that they also occurred in the "gigantic ground-living fossil sloths"). It is reasonable to deduce that ground sloths either shared the clinging habit of modern sloths, or more likely, they evolved from tree sloths with this habit and retained the venous arrangement in the spine.

Here is something relevant from the Wikipedia article on sloths:

"The two-toed sloths of today are far more closely related to one particular group of ground sloths than to the living three-toed sloths. Whether these ground-dwelling Megalonychidae were descended from tree-climbing ancestors or whether the two-toed sloths are really miniature ground sloths converted (or reverted) to arboreal life cannot presently be determined to satisfaction. The latter possibility seems slightly more likely, given the fact that the small ground sloths Acratocnus and Neocnus which were also able to climb are among the closer relatives of the two-toed sloths, and that these together were related to the huge ground sloths Megalonyx and Megalocnus."

Julian

2012-01-09T02:56:00.000-08:00

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Canines as human commensals: were dogs domesticated because as scavengers they kept the camp clean and (relatively) hygienic?

Another topic I plan to write about.

Julian

2012-01-08T19:25:00.000-08:00

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Why can't modern people wipe out vertebrates?

I hope to write a bit about an issue that occurred to me recently. Claudio Tuniz and his co-authors write about the apparent wiping out of the flightless bird, Genyornis, by early Aboriginal man in "The Bone Readers" (2009). There is a longstanding debate about whether early humans in places like North America and Australia drove some prey animals to extinction through hunting. In this case, the evidence seems quite strong that they did.

What puzzles me, and what I am reading about at the moment, is why on the other hand it seems pretty generally accepted in some quarters that it is effectively impossible to eradicate pest vertebrates, such as feral pigs or feral goats, from the Australian continent, even with modern methods.

Why can modern man not do what ancient man did?

Julian

2011-11-06T16:16:00.000-08:00

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The Selfish Chromosome: Why Sex Evolved

By Julian David O’Dea, PhD, Department of Health and Ageing, Canberra, ACT, Australia

The problem of why sex evolved in the first place and why it has been maintained in most higher organisms continues to puzzle biologists. Theories have tended to focus on the advantage of sex to the individual or to the population. Popular explanations focus on the advantage of genetic recombination (for example, in providing variation in an evolutionary contest with parasites) or on the usefulness of sex in removing deleterious mutations from the population.

This note proposes that sex evolved because it was (and is) to the advantage of genetic material (chromosomes, for example) to recombine with other genetic material, that is by way of amphimixis (sex). It is assumed that defective or low-quality genetic material (chromosomes, genes) has always been and still is a besetting problem. From the perspective of the “interests” of the bulk of the genetic material, it is desirable to be in an organism with as good quality a genome as possible. That is, as free of deleterious mutations and defective DNA as possible. Obviously such genetic material, in such an organism, will proliferate best.

An organism is likely to possess some lower quality genetic material. If it possessed a lot, it would not be viable. But even a viable organism is likely to have or acquire some substandard genetic material, either by inheritance or mutation or because a changing environment renders some of the genes ineffective or redundant.

What sex does is allow the genetic material in an organism to combine with new material. In most cases, there will be no net benefit, because the amount of deleterious genetic material in the new genome is likely to be, on average, the same as before sex. So, there is no net advantage to most of the genetic material from sex. However, in a substantial proportion of cases (25% in a typical example), the genetic material improves its situation after sex because the deleterious material is lost. The effect of this is to improve the quality of the genome and the organism will therefore proliferate, and the genetic material along with it.

This advantage is multiplied as sexual generations pass. There is a continual improvement, at least relative to asexual organisms which are less able to shed deleterious mutations.

In a single celled organism which proliferates primarily by mitosis, with intermittent meiotic events attendant on sex, any genetic material lost to the ill effects of sex causing the accumulation of deleterious mutations in some individuals will be more than offset by the advantages to the genetic material in cases where all the deleterious material is removed. In the latter cases, the selective advantage will accrue strongly as the organisms proliferate mitotically. In the case of multicellular organisms, there are typically abundant progeny to allow the advantages of really good combinations to accrue to the genetic material which is coding for amphimixis. Some progeny will be lost due to unfortunate genetic combinations, but this will likely be more than offset by the very good combinations produced, which will survive and proliferate exceptionally well (thereby favouring the genetic material itself).

An earlier version of this theory (O’Dea, 2006) was cited in Glansdorff et al. (2009) in the context of their proposal that sex evolved to remove exogenous DNA, in particular from horizontal gene transfer.

As an example, consider two cells, each of which is diploid. If one assumes that one of a (different) chromosome pair in each organism is defective in some way, sexual reproduction will result in no net change in 50% of cases. That is, the new organism which results from amphimixis will have the same number of defective chromosomes (one). In 25% of cases, it will have two, because it acquires both the defective chromosomes from the parental cells. But in 25% of cases, it will have no deleterious material. Such an organism (and its constituent genetic material) will be expected to proliferate exceptionally well, better than asexual organisms unable to readily expunge deleterious DNA from the genome. A similar calculation was provided in O’Dea (2006).

In conclusion, this proposal places the emphasis on the advantage of sex to the genetic material coding for sex, rather than to the individual organism or the population. The level of selection is at the genetic material itself; for example, the chromosomes will be the units of selection, a concept reflected in the title of this note.

References:

Glansdorff et al. (2009). The Conflict Between Horizontal Gene Transfer and the Safeguard of Identity: Origin of Meiotic Sexuality. Journal of Molecular Evolution 69: 470-480.

O’Dea (2006). Did Conflict Between Chromosomes Drive the Evolution of Sex? Calodema (Sydney, Australia) 8: 33-34.

2011-07-08T19:50:00.000-07:00

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Genetic Material Itself Drove the Evolution of Sex

Julian O'Dea

The basic problem with previous theories to explain the evolution of sex is that they focus on the wrong levels of selection, namely at the individual or population level. I think it is more productive to focus on what about sex is advantageous for the genetic material itself, for example the chromosomes.

To follow up my previous post of 4 April 2011 on this issue, I want to broaden my argument a little. I have already published the basic idea and it has been cited in the Journal of Molecular Evolution. Further thought leads me to have confidence that I am on the right track. Sex evolved because it is to the advantage of the genetic material in a cell or organism to combine with that from a different cell. The reason is that this allows the genetic material to constantly find better environments by escaping from poor quality genetic material (e.g. damaged chromosomes, serious mutations).

To take a simple example, consider two cells with several diploid chromosomes. Assume each cell has one of its chromosomes in a pair with a serious defect. For most of the genetic material, it is easy to see that following sexual exchange of chromosomes between two such cells, there is a 25% chance that it will be found in a cell with both defects, a 50% chance of still being in a cell with one defect and a 25% chance of being in a cell with no defects. The last case is crucial. This new cell will have a major adaptive advantage. Putting it another way, its genetic material is likely to survive and thrive.

The advantage for normal genetic material in coding for sex, rather than asexual reproduction, is that it permits the genetic material to constantly escape from damaged and deleterious genes and chromosomes.

2011-04-09T22:57:00.000-07:00

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Another reference to my idea on African lips, mentioning African fashion model

A reference from a French site on African beauty to my post here on the adaptive function of "African lips":

http://beaute.afrik.com/forum/index.php?topic=1866.msg34767#msg34767

The model they mention is Alek Wek:

http://www.short-hair-styles-magazine.com/images/ultra-short-female-haircuts-11_ALEK_WEK_3-1.jpg

Julian

2011-04-06T03:23:00.000-07:00

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More on Pygmies and ultraviolet light

I have blogged before about the theory I published years ago - that Pgymies and Negritoes have short stature because of a shortage of ultraviolet light in the rainforest. Low ultraviolet light might mean low vitamin D production in the skin and therefore low ability to take up calcium for bone growth.

Since then, there have been a number of developments. An essential part of my theory, obviously, is that ultraviolet light levels in the rainforest are indeed low. I measured them some time ago, and I have cited the low levels at my blog here. These results were originally published in the Australian Society for Human Biology Newsletter, but they are no longer available online. However a good set of data, showing the same very low ultraviolet (UV-B) levels I found, again from North Queensland, have been reported more recently by Frances Baines:

http://www.reptileuvinfo.com/html/uv-light-in-daintree-rainforest-northern-queensland.htm

She measured ultraviolet light in the Daintree Rainforest. I measured values near Kuranda, inland from Cairns. Frances Haines seems to be quite a busy woman, with a special interest in ultraviolet light and reptiles. She is affiliated with The Citizen Scientist group:

http://www.sas.org/tcs/index.html

Another nice reference to my ideas on Pygmies, Negritos and the "Australian Pygmy" tribes from the Queensland rainforests was that given my work by Peter Hiscock, the noted archaeologist, and his colleague Michael Westaway:

http://www.kooriweb.org/foley/resources/pdfs/164.pdf

It was interesting to see my work cited in such a politically charged atmosphere.

My theory on Pygmy stature also got a run in Peter McAllister's recent popular book, "Pygmonia":

http://petermcallister.com/Pygmonia.html

although the author ends up favouring a life cycle theory to explain Pygmy stature. The book is a good read though.

Finally, it was strange to find my ideas on the adaptive function of African lips in signalling health referred to in a peculiar, racist book:

http://erectuswalksamongst.us/Chap10.html

Julian O'Dea

(the person who "signs" these posts, Karna O'Dea, is my wife, because the computer account seems to be in her name.)

2011-04-04T04:39:00.000-07:00

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Wide ranging implications of a chromosomal conflict model of the evolution of sex

In 2006, I published a theory of the evolution of sex, with a paper in the journal Calodema entitled "Did conflict between chromosomes drive the evolution of sex?" The short paper is available here:

http://julianodea.blogspot.com/2005/12/odea-j.html

The paper is cited at the Wikipedia article on intragenomic conflict:

http://en.wikipedia.org/wiki/Intragenomic_conflict#Evolution_of_sex

Since then, this paper has been cited by Glansdorff et al.:

http://www.springerlink.com/content/27754583788u0784/

Over the next few months, I hope to add to this post a discussion of the various possible ramifications of my theory, which has already proved useful to Glansdorff et al., in their paper in the Journal of Molecular Evolution entitled "The conflict between horizontal gene transfer and the safeguard of identity: origin of meiotic sexuality". This paper in the Journal of Molecular Evolution has itself been cited three times already.

It seems to me that my theory of chromosomal conflict driving the evolution of sex may have implications for many areas of biology. I hope to expand on that theme here over time.

2009-12-21T17:59:00.000-08:00

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Ultraviolet light levels in the rainforest

I made some measurements of UV-B light in rainforest in North Queensland some years ago. They relate to a theory I have published on the evolution of pygmy stature in humans, which I attribute to low ultraviolet light levels in this environment (under the rainforest canopy).

My theory is cited here:

http://en.wikipedia.org/wiki/Pygmie

The data were published in a newsletter put out by the Australasian Society for Human Biology, but are no longer available on the Internet. So I shall give a summary of the results here.

I used an ultraviolet light meter to take readings in rainforest at Kuranda and nearby regions in North Queensland in August 1994. The readings in the open - outside the rainforest - during fine weather ranged from 70 to 245 units. The readings inside the rainforest ranged from 0 to 5.

To take one example, on 5 August 1994, at 11.00 am in rainforest near Kuranda on the Mareeba Road, North Queensland, I obtained a typical reading of 1 unit of UV-B. In the open, outside the rainforest, I obtained a reading of 189 units. Taking these readings inside and outside the rainforest at the same time was fairly easy, as the rainforest was beside the road.

It was clear that the rainforest canopy cut off almost all the ultraviolet light and prevented it from reaching the forest floor. The Aborigines who used to live in these rainforests would have been exposed to low ultraviolet light levels.

There is surprisingly little published on ultraviolet light levels in rainforest. It is well-known that it is gloomy inside a rainforest, but what is not so well-known is that ultraviolet light levels, of the kind that help human skin make vitamin D, are particularly low.

Julian

2008-12-05T14:07:00.000-08:00

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Human communication as "polling behaviour"

Fairly regularly, I ask my daughter "how she is". I just asked myself why I do this, apart from fatherly interest and concern.

It occurred to me that I am just checking her current state of morale and happiness. Checking that she is OK and there is nothing she wants to complain about.

It reminded me fleetingly of something I learned about in computer science, "polling". In some computer set-ups, one device repeatedly checks on the status of another, to see if it has any data to submit for example. It occurred to me that one function of human verbal communication is simply to check a couple of basic things 1) that the person is there and 2) to gauge their emotional state (from language cues such as intonation). Robin Dunbar has suggested that language is a form of social grooming, but it seems to me that it can also be seen as a way of quickly polling other people on their "current status". Think of a morning greeting - generally very perfunctory - which really only conveys presence and gives a rough indication of mood and readiness for the day's activities.

Anecdotally, parents seem to "poll" their children verbally more than vice versa. And wives seem to "poll" their husbands more than vice versa. In both cases, a grunt may be all that the parent or wife gets back. At least a grunt signifies presence.

Julian

2008-11-17T22:23:00.000-08:00

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Predictive Biology

Like many biologists I imagine, I was delighted with this story, about a species of ant in which a few ants, each night, make it their business to seal the nest from the outside. This means that the colony is safer but the ants left outside die.

While biology is not particle physics, with the existence of new particles predicted by theory, it should be possible to predict biological phenomena to some extent at least. Knowing that worker ants and other social insect workers are altruistic (bees dying when they sting; termites that literally explode to protect the colony), it would not have been hard to predict the existence of ants that sacrifice themselves by sealing the nest from the outside. A few minutes thought would have done it.

Similarly, lazy ants and male stuffing in wasps could have been predicted from first principles.

I am aware of at least one prediction from first biological principles, by the McMenamins, as part of their "hypersea" hypothesis:

' Yet another test would be to look for organisms that exploit Hypersea in ways allowed by the hypothesis but that are thus far unidentified. For example, just as marine animals have become terrestrial parasites, photosynthesizing algae or bacteria should also find an animal to be a fine aquatic habitat. Mark suggests that there are (or once were) terrestrial counterparts of the Ediacaran fauna, animals that survive by hosting photosynthesis. "Whenever I give a lecture on Hypersea," says Mark, "someone comes up to me and says, 'I think there's one out there, too, and I'm going to find it.'" Mark himself will hunt for fossils of such life-forms. "I want to go into the Appalachian Mountains and look for evidence of unusual hypermarine linkages in these kinds of organisms. Maybe my photosynthetic land animal is there." '

Not quite what McMenamin had in mind, but pretty close, is the case of the South American sloth, which has symbiotic photosynthetic bacteria in its fur:

http://en.wikipedia.org/wiki/Sloth

" In moist conditions, the fur hosts two species of symbiotic cyanobacteria, which provide camouflage[3][4]. The bacteria provide nutrients to the sloth when licked during grooming.[citation needed] Sloth fur is also host to algae; this algae colors the coat green and acts as camouflage.[3] Because of this algae, sloth fur is a small ecosystem of its own, hosting many species of non-parasitic insects.[5]. "

It seems likely that to be a terrestrial animal hosting photosynthetic symbionts one would have to stay still and spend a lot of time in the sun. The sloth's arboreal life and slothful ways would probably meet this requirement.

Some time ago, as I wrote here on this blog, I made a theoretical prediction which turned out to be true in one instance at least. Here is what I wrote:

Plants as Doctors?

For some time, I have toyed with the idea that plants might provide substances of medical value to animals that perform useful services for them. For example, do fruiting plants provide medically useful chemicals to monkeys that eat their fruit and help spread their seeds? Could plants provide some curative products to animals that eat their foliage? That is, could a plant's leaves or fruit provide chemicals designed to help prevent or cure animals' diseases?

Certainly plants frequently secrete materials that are intended to stop animals from feeding on them; but could they do the opposite and encourage the health and survival of animals that render them services - such as spreading their seeds or fertilising them with their droppings - by providing them with useful medications? Is it possible that some of the useful drugs that are derived from plants have their origin in keeping wild animals healthy - for the mutual benefit of the plants and animals? Is this one reason why fruit seems to be so valuable in the human diet?

There is one case that appears to show "proof-of-concept". For an account see "New Scientist" (UK) - the issue of 30 May 1998, p.27. The note is short so I'll quote it in full:

" A Beautiful Way to Keep Bees Healthy

This flower [illustrated], which is native to South and Central America, lavishes an unexpected gift on the wild trigona bees that pollinate it - a coat of resin spiked with powerful antibiotics that probably help keep their nests free of harmful bacteria. John Loquvam of the University of Alaska in Fairbanks exposed bacteria known to infest the hives of honey bees to the resin of the flower, *Clusia grandiflora*. The resin was almost as effective at killing the bacteria as conventional antibiotics. 'It's the first time this has been shown in any plant as a pollinator reward', says Loquvam. Resin from the female plants was far more potent than extracts from male plants. Loquvam suspects the females are compensating for the fact that males produce 15 times as many flowers. "

It seems likely that this principle - of plants providing useful animals with medicinal rewards - will be found to apply in other cases as well. It would certainly be in the interests of plants to ensure that useful animals remain free from illness and able to continue to serve the plants' purposes.

Julian

2008-11-17T01:48:00.001-08:00

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More special pleading on the honeybee dance language

From page 17 of the New Scientist magazine of 4 October 2008:

" When honeybees dance to point their hivemates towards nectar-rich flowers, they waggle in a slightly different direction each time. It is sometimes claimed that this variability benefits the hive by helping bees locate new resources ... etc. etc. "

This doubtful theory is replaced by another one that requires the honeybees to "keep a mental log of the directions indicated in the dance" and take the mean. As one of the authors remarks, "I find it remarkable that, with a relatively simple brain, they can do something so mathematically complex". So do I!

The honeybee dance language hypothesis has had many ad hoc corrections applied to it over the years, and this is simply the latest. The whole thing is getting beyond a joke. There are other explanations for the apparent dance language, as I argued several years ago,

Here.

My proposal, that the so-called dance language is simply idiothetic behaviour, is also discussed at the following Wikipedia article on honeybee behaviour.

Julian

2008-10-27T02:43:00.000-07:00

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More on the evolution of sex

I have written and published on this before. Here, for example.

What I have tried to show is that conflict in a cell between a majority of normal, functioning chromosomes and a smaller number of ineffective, parasitic chromosomes could have led to the evolution of sex. This is because the recombination of chromosomes due to gamete and zygote formation would have tended to advantage the normal chromosomes and disadvantage the parasitic chomosomes. I have given the results of the relevant simple calculations at the above link.

It occurred to me recently that the relative advantage for normal chromosomes in sexual reproduction would be strengthened in the case of multicellular organisms, since they can produce many gametes and the statistical likelihood is that - for the normal chromosomes - there will be a definite advantage in sexual reproduction. However in the case of a single celled organism, sexual reproduction is more of a risk because although it is likely that it will leave a normal chromosome better off, it is not certain, as there is a small risk that it will end up worse off. This might help explain why sexual reproduction is more typical of multicellular organisms.

2007-11-19T18:11:00.000-08:00

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The hymen as honest signal

A recent set of comments on an evolutionary psychology [sociobiology] discussion list:

JB: In monogamous species, the threat to the male (from the female) is cuckoldry, and the counter-threat to the female (from the male) is abandonment. The presence of the hymen is a clear signal to the male that the female is not promiscuous (or at least hasn't been so far), that she is prepared to make sacrifices for this particular male, and so on -- all of which seem to serve the purpose of diminishing the above threat and counter-threat. As a rule of thumb, anything that happens to serve a biological purpose well should be considered as an adaptation for that very purpose.

RB: In Japan some women pay to have their hymens repaired after sex.

EO: Iris claims that you and she believe that human females have no hymen pain at first intercourse. No doubt for some cases this is true, however I know that losing a hymen can be extremely painful and that anticipation of this pain can exercise a powerful inhibitory effect against first intercourse. I remember well being in the next room to my buddy and his girlfriend as he tried repeatedly all night to overcome her fear and pain. She wanted to do it but was nearly hysterical with fear and was yelling and crying with pain much of the night from his repeated attempts. I didn't get a wink of sleep all night because of the racket. This girl had been putting off her boyfriend for a year or two for this reason, so having a hymen was definitely delaying the age of first intercourse for her.

SM: Yes, virginity in a female mate is obviously prized by a male. 1. She can't be already pregnant by another male. 2. She can't have in her genital tract sperm from another male to compete with his. 3. She is likely not to already have a mate or even a suitor, and therefore won't be 'mate guarded'. 4. She is at the very start of her reproductive life and not far short of the peak of her fertility, so any sex that may lead to a pair bond could lead to a lot of sex and reproduction in the future. It takes a determined ignorance of EP [evolutionary psychology] to not see the value of virginity.

Julian: Thank you, J and S, for amplifying my original suggestion, which I now think may have real merit. I have yet to check Daniel Rancour-Laferriere's useful book on such topics, which may cover this issue. To add to R's comment, Greek girls in Australia are reported to get hymen reconstructions for cultural reasons and the same is true in the Muslim world by all accounts. E's experience reflects my own. I used to read my sister's girls' magazines, and one of the commonest letters to the editor asked if tampons would affect a girl's hymen. Clearly modern women are still concerned about such issues.

Thank you to J-e for her recent long posting, a quotation which tends to confirm my understanding of the facts. The human hymen has acquired great cultural significance as a marker of virginity. When asked what it was for, many pious folk would have said that it is God's way of showing that a young woman is pure (a view I have some sympathy with); more scientific folk would have referred vaguely to hygienic advantages. But, from an evolutionary psychology perspective, I think it is quite fruitful to see it as a form of honest signalling and its existence as contributing to successful pair bonding.

Julian

2007-11-16T17:39:00.000-08:00

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Google Maps

Google Maps provides excellent satellite pictures.

I wonder how much zoogeomorphology would be visible in the satellite images.

Places to check out with Google Maps and Google Earth: Florida everglades, Nullarbor Plain, Congo Basin, rainforest near Cairns.

Another interesting thing to do would be to search for doubtful islands, such as those discussed by Henry Stommel.

Julian

2007-10-21T03:02:00.000-07:00

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Catholic countries: warm and lazy

Recent comments on blogs about the economic weakness and general chaos in Catholic countries (and even "Catholic cities" like New Orleans) have made me think about that classic problem: why are Catholic nations often backward in these respects? Most people would be aware of the classic explanation from Max Weber, centreing on the idea that Calvinism and the Protestant Work Ethic led to greater economic success among Protestants than Catholics. A lot of recent rhetoric contrasts the superior work ethic of WASP Americans with that ascribed to the Hispanics now flowing into America, legally and illegally.

It certainly seems that Catholic countries lag. One need only compare Latin America to the heavily Protestant United States. The British Prime Minister, Lord Salisbury, of all people, writing in the 19th Century and worrying about the Irish, did however admit that Catholicism itself was not necessarily the problem. He noted that Belgium had a lot of Catholics as well as economic success.

One factor that I can't remember being suggested to explain the disparate success of the Catholic South of Europe or South America with the Protestant North of Europe and North America is simply this: a warm climate versus a cold climate. By historical accident, the more Protestant parts of Europe are also mostly the colder parts. Life is harder in colder climates, and the strongly seasonal nature of agriculture would have required more planning and hard work. As the (mostly Protestant) South in the United States demonstrates, warmer climates lead to easier living and a more leisured society.

It could be argued that Catholic nations Poland, Ireland and Quebec are comparatively cold and have also been backward, although a case could be made that these countries suffered from bullying neighbours. Ireland at least is doing rather well these days. Other instructive cases are those of Bavaria and Austria, both of which enjoy economic success, despite being Catholic. And they are cold.

So, a factor that should be considered in the debates about the "laziness" of Catholics, including Hispanics, is that it may be due in part to their living in warmer climes which make working hard neither particularly necessary nor particularly appealing.

Julian

2007-10-12T18:41:00.000-07:00

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Why the Internet Autism Test is probably not reliable

A test of one's Autism Quotient is readily available on the Internet. Its most famous appearance may be in an article in Wired magazine, which included a copy of the test. Many people have taken the test and seem to take a perverse pleasure in scoring high, thereby identifying themselves as somewhat autistic and therefore as true "geeks".

Reference to a scholarly paper by those who developed this test makes me suspect that the self-diagnostic approach to the test is flawed. Checking the fine print, we find this:

" ... 80% of adults with AS or high functioning autism scored above a critical minimum of 32, whereas only 2% of control adults did. "

What this is saying, as far as I can see, is that people known to have autism generally scored high on a test designed to test for autistic traits. OK. But it is then noted that 2% of control adults scored high as well. What does this imply? That 1 in 50 people in the ordinary population will score as "autistic". Autism is generally considered to be a rare condition. But 1 in 50 people is a very high number of people. Clearly this test will produce a lot of false positives, with large numbers of people with no clinical condition scoring into the abnormal range associated with autism.

One of the signs of autism is social withdrawal. However to be shy and socially withdrawn - to be scholarly in other words - is not to be autistic. I feel that people are testing themselves for a symptom of a disease, and then deciding that they have the disease. It's a form of hypochondria.

To use an analogy, perhaps 2% of the male population is over six feet two inches. Men with excess growth hormone will mostly be over six feet two inches. But that does not mean that everybody over six feet two inches has a hormonal problem.

Julian

2007-07-08T04:18:00.000-07:00

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Note to self

Follow up:

Calcium-sparing and the "Hobbit"

Female buttocks and spanking

Polygamy and sisters

2007-05-30T03:16:00.001-07:00

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Music and Genes

Dusk in Autumn suggests here and here that human groups with high spatial intelligence will tend to produce music that is harmonic rather than melodic:

" Last year I wrote up some suggestive evidence that in order for a group's musical style to emphasize harmony (or the "vertical" aspect of music), a necessary but not sufficient condition was a cognitive profile that either was lopsided toward Spatial rather than Verbal IQ or was balanced. "

The Chinese are generally understood to have a high spatial IQ relative to verbal IQ, as Dusk in Autumn himself notes, and yet, as this article indicates:

" All traditional Chinese music is melodic rather than harmonic. "

Dusk in Autumn apparently recognises that the Chinese case does not provide evidence for his theory.

Another way of looking at the problem is to note that melody includes a " ... succession [which contains] ... change of some kind and [is] perceived as a single entity ... to be called a melody. Most specifically this includes patterns of changing pitches and durations ... " and, as already noted, Chinese music is " ... melodic rather than harmonic. Chinese vocal music probably developed from sung poems and verses with music. "

It is not hard to imagine that a tonal language like Chinese would predipose towards a melodic style of music. In fact, an interesting piece of recent evidence suggests that a capacity to speak using tonal languages like Chinese may vary to some extent based on some brain development genes. I wonder if this genetic tendency towards tonal expression might explain the melodic rather than harmonic emphasis of Chinese music.

Julian

2007-04-03T05:08:00.000-07:00

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An interesting idea on cats, humans and toxoplasmosis

I have always wanted to use this blog not just to present a few ideas of my own, but to showcase ideas that I find particularly noteworthy. This may be because I think they are exciting and likely to be true, or exciting if dubious, or popular but probably mistaken. In the second category, I place this one from a blogger calling himself Dusk in Autumn.

Julian

2007-03-25T21:17:00.000-07:00

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Why rainforests are "hot zones" for diseases?

Forrest M. Mims III has suggested that when there is mass burning in an area that produces large amounts of smoke, the resulting decline in UV-B light levels may permit higher levels of pathogenic airborne bacteria and viruses to build up, with possible human health implications.

An environment in which UV-B levels are permanently low is the rainforest. Some years ago, I measured UV-B levels in a rainforest in North Queensland. I found that, as expected, the levels of ultraviolet light on the floor under the rainforest canopy were very low.

A number of serious viral diseases have emerged from the rainforests of Africa in recent years:

"Among the extraordinary biodiversity of rainforests are a multitude of viruses and other diseases that have not yet come in contact with humans. Viruses, which previously remained hidden in remote rainforests suddenly have access to large human populations. The appearance of such "rainforest diseases" as HIV/AIDS, Ebola and Marburg suggests that these could result from tropical deforestation. The rainforests hold such viruses in check, but without the forests to 'lock' them in, they would be free to infect humans and other species."

But why are such viruses endemic to rainforests? It seems possible that the lack of ultraviolet light in the rainforest could allow them to thrive in that environment. Are these pathogens airborne? Marburg virus may be. Ebola may be, at least between monkeys and perhaps in humans.

Here is a note by Mims on UV-B as a controlling factor on influenza viruses. However these people, writing about foot-and-mouth disease virus in Australia, tend to discount a role for ultraviolet in limiting the spread of this virus at least.

Julian

2007-02-13T00:32:00.000-08:00

Testing the new blogger.

Julian

2006-11-29T01:41:00.000-08:00

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The function of cholinesterase in red blood cells and plasma

This is just a note to myself to do some thinking about this. Apparently, whereas the function of cholinesterase in the nervous system is of course well known, the function of the same acetylcholine degrading enzyme in red blood cells and plasma is not known. It seems likely to me that since plasma and red cells get everywhere in the body, having cholinesterase in the plasma and on red cells could help mop up any acetylcholine that leaks away from neurones (specifically from the synapses).

I once measured red cell cholinesterase during my Ph.D. One interesting thing about this red cell enzyme is that it is located on the outside of the red cell, which would fit with its having the kind of role I am thinking of above.

Still, more work needed ...

Julian

2006-11-24T01:10:00.000-08:00

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"Calodema" Comes of Age

Well, "Lucky Seven" indeed. The seventh issue of "Calodema" - "devoted to promoting knowledge about the flora and fauna of Australia and the Pacific" - is the best yet. As usual, the cover is adorned with a fine photograph of Calodema regale, a stunning Australian jewel beetle (family Buprestidae). This issue also includes a paper by the Editor, Dr Trevor Hawkeswood (email: drtjhawkeswood@calodema.com), reviewing the biology and host plants of this species. (On a personal note, I am fairly sure that this beetle was the model for a colourful beetle-shaped chocolate that used to be sold when I was a child.)

Here in Canberra, the local authorities put out posters warning us against eating Amanita phalloides, the death cap mushroom. This is not an Australian native, but an introduced species. Another introduced member of this notorious genus is Amanita muscaria. Trevor reports on finding this fungus in association with a "mini-plantation" of Pinus radiata (Monterey or radiata pine) trees at Wentworth Falls, Blue Mountains, New South Wales. The fungus is not merely associated with this introduced tree, but is starting to invade native habitats such as wet and dry sclerophyll forests. Trevor gives the details in his paper.

Last night I found two spiders on the roof of our car. When disturbed, one remained still, presumably relying on camouflage. The other bounced around as my finger teased it, bounding about while keeping an eye on my finger. Ah, I thought, that's a salticid, a "jumping spider". The salticids are the largest family of spiders, chiefly famed for their beautiful eyes and excellent vision. This issue of "Calodema" includes further contributions from Dr Dewanand Makhan on new species of jumping spiders from Suriname. This brings me to one of the best new features in this issue of Calodema, the sepia-toned photographs, which illustrate several of the articles, including Dr Makhan's new spiders and beetles.

Surely unique must be the account in Calodema No. 7 of a possible envenomation from an "antlion" (of the insect order Neuroptera). The reported bite on a finger seems to have had a more than local effect, with pain extending up the arm. Very little seems to be known on what kind of venom or digestive fluid antlions can deliver. Some people doubt whether they have a true venom. This case report provides evidence that they indeed might.

Also in this issue is a stringent critical review of a paper on the pollination of Australian orchids. This review refers to the interesting suggestion that capture by spiders might help identify the insects that pollinate orchids. If so, perhaps the spider could be offered co-authorship.

There is plenty of other material, but a paper I found of particular interest was on the fairly obscure beetle family Ceratocanthidae, the "pill scarab beetles", which can roll themselves into little balls. This makes them cryptic. This ability to roll up might also provide some physical protection, and it made me consider how many other animals are capable of curling right up. These include pillbugs on land and Nannosquilla in the ocean (Crustacea), pangolins, armadillos and hedgehogs (Mammalia), some salamanders (Amphibia), and the caterpillar of the moth Pleuroptya (Lepidoptera). The caterpillar not only rolls up but rolls away to escape.

Obviously I found plenty of inspiration from Calodema No. 7, and I recommend this issue as another milestone in the development of this journal.

Julian

2006-10-14T03:11:00.000-07:00

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Non-Paternity ("cuckoldry")

Rampant paternity fraud an 'urban myth'.

I have been interested in the (over-)estimation of non-paternity in modern society for some time. See my post here.

Figures of "10%" of children not being those of the nominal father of the family have been bandied about a lot in recent years. The figure seems prima facie too high. Also it seems inconsistent with the extraordinary rates of 'breeding true" seen in some populations, for example in the case of the Jewish priestly Y chromosome:

" One marker, however, present in more than 50% of Eastern European [Ashkenazi] Jewish Levites points to a common male ancestor within the last 2000 years for many Levites of the Ashkenazi community. "

I suppose it is possible that the Levites historically lived in separate communities, which might explain the tendency for the relevant Y chromosome to breed true, even in the presence of cuckoldry.

I should say one thing though. A low level of non-paternity (or cuckoldry in the sense of a woman bearing a child not her husband's) does not necessarily imply a low level of adultery. It is perfectly possible for wives to have historically had sex outside marriage in relatively large numbers. This is because between 25 and 50 acts of intercourse are typically required to produce one conception. So, my remarks in my earlier post about the apparent "good behaviour" of our ancestors were a bit naive.

Julian

2006-08-26T05:15:00.000-07:00

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Indonesian scientists and others claim the "Hobbit" was only an aberrant pygmy

Here is the article from PNAS. Here is an interesting passage referring to the small size of the Hobbit (designated Homo floresiensis by some):

" Reduction in size on Flores is unsurprising in an ecosystem characterized by a humid climate, hilly topography, and abundant undergrowth of vegetation. Maintenance of body temperature alone can be a sufficient selective factor for small body size in such surroundings. Selection need only be sufficient to overcome limited levels of gene flow expected on an island separated by stretches of water constituting just filter barriers. Many of the surrounding regions (Peninsular Malaysia, the Andaman Islands, Sumatra, Java, Sulawesi, Papua, and Northern Australia) include populations relatively short in stature ... Diminutive body size does not in itself constitute convincing evidence for either isolation or speciation, because size fluctuations occur repeatedly in mammalian, including human, lineages. In living African pygmies, for example, spatial and genetic isolation manifestly is incomplete. "

In my view, the Hobbit was probably adapted to a rainforest environment, like most of the very short-statured peoples around the world. Also, as I have published, the most likely feature of the rainforest that is unique and probably results in a small skeletal size is low ultraviolet light, leading to low capacity for vitamin D production and development of bone mass.

(The Northern Australian pygmoids referred to in the quotation above are presumably the rainforest Aborigines of North Queensland. I measured ultraviolet light levels in the rainforest there some time ago. My report is here.)

It is interesting to see Australian Professors Thorne and Henneberg on the list of authors of the above paper. Professor Thorne is a noted physical anthropologist who lives here in Canberra and has been associated with the multiregional hypothesis of modern human origins, and Professor Henneberg is based in Adelaide and has presented his suggestion that the "Hobbit" individual was a case of microcephaly at a meeting of the Australasian Society for Human Biology (ASHB).

The above paper in PNAS argues that the Hobbit individual was an abnormal (microcephalic) person from a pygmoid population of modern humans. The suggestion that I made (from the floor) at the abovementioned meeting of the ASHB was that the Hobbit would turn out to be an extreme pygmoid type of Homo sapiens. This is close to the conclusion in the PNAS paper, except that I did not suggest that the individual was microcephalic, just an extreme type of pygmoid. Here and here are Internet references to my proposal.

John Hawks has also discussed this new PNAS paper at his anthropology blog.

I await further developments with interest.

Julian

2006-08-17T00:35:00.000-07:00

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More on "walking trees", the science of miracles

Following on from my post below, I have found, via this blog, that yet another writer has made the same point about the miracle at Bethsaida. This time it is "D Keith Mano", who is apparently quite a well-known writer and associated with prominent conservative American magazine, National Review. Here is his article, entitled "The Bethsaida miracle - Jesus healing a blind man." Here is a quote:

" But, at Bethsaida, something quite different came about: a miracle that depends on science for its proof, that cannot be understood except by adducing modern medical data --quite unknown in 30 A.D. -- as evidence. And, when one miracle has been proved, it then at once becomes not just possible, but probable, that another miracle can also be proved true. "

Mr Mano makes the same point as Mr Grigg. I should clarify my earlier post by stating that, although I wrote about two New Testament miracles involving Christ curing blindness in my own article, I did not make explicit the point that Messrs Grigg and Mano have both made: namely how impressively believable the New Testament account of the miracle at Bethsaida has become in modern times, because of our modern understanding of the nature of vision and perception.

Julian

2006-08-06T01:30:00.000-07:00

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"Walking Trees": The science of the miracle at Bethsaida

In 1994, I wrote about the perceptual psychology of the New Testament accounts of the curing of blindness in St Mark's Review, an Anglican journal based here in Canberra. The article was entitled “Seeing is perceiving" and appeared in No. 159, pp. 30-31. I have a copy on the Internet on this page (scroll down). I mentioned the case of the curing of "the Man Born Blind" and also the miracle at Bethsaida, in which case the blind man famously remarked after Jesus first attempted to cure him that he "saw men, like trees, walking"; after which Jesus completed the cure and the man saw clearly.

In 1995, famed neurologist and writer Oliver Sacks referred to the miracle at Bethsaida in a footnote to a chapter of his book "An Anthropologist on Mars". He had similarly written, in a 1993 essay in The New Yorker on which the chapter was based, that "There is a hint of it even in the Bible, in Mark’s description of the miracle at Bethsaida; for here, at first, the blind man saw 'men as trees, walking,' and only subsequently was his eyesight fully restored."

In 1999, Australian Creationist writer, Russell Grigg, wrote a good article on the same point in the journal "Answers in Genesis". He cited Professor Sacks, but not my article in St Mark's Review, which covers many of the same points made by Mr Grigg. While I am not a Creationist, I am pleased that Mr Grigg is as impressed as I am by the possibility that the New Testament account gains believability when we consider what modern medicine now knows about vision and perception. I think it is an exciting point, which deserves a lot more attention.

It is interesting that Professor Sacks (a secular Jew, I understand) simply alluded to the curious nature of the Bethsaida miracle story, with its hint of an optical cure followed by a separate perceptual cure. I, on the other hand, implied that the account of the miracle is made more believable by what we have learned since Biblical times about sight and vision. Finally, Mr Grigg stated this point very directly.

Julian

2006-07-18T05:15:00.000-07:00

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The function of itching and scratching

For quite a long time I have wondered about the function of itching and scratching. Here is some discussion on the topic involving some of my thoughts, from the old Ethology discussion group on the Internet.

I have an article from a book called "Imponderables", which asks the question "Why do we itch?" and replies that the short answer is "we don't know". This book was written in the 1980s and it reports that the same receptors and nerves carry both itching sensations (when they operate at a low level of activity) and pain. However, it now appears that when itching is caused by histamine, specific nerve fibres for itching are involved.

I recently came across a paper by Choi and Maibach (Skin Pharmacology and Applied Skin Physiology 2003; 16: 271-282), entitled "Topical vaccination of DNA antigens: topical delivery of DNA antigens". This paper noted that when skin is damaged, keratinocytes and Langerhans cells become activated. Disruption of the skin barrier results in epidermal Langerhans cell activation as vigorous antigen presenters for T helper cells (that is, an immune response). The level of skin damage required is quite minor. "Stripping" the skin using tape or the removal of dried glue from the skin is sufficient.

Stripping the skin also enhances the effects of topical DNA vaccine. That is, topical application of DNA vaccines with stripping induces stronger immune responses than without stripping.

In conclusion, it seems likely that a key function of itching in humans is to provoke scratching of the skin, with the resulting mechanical disruption leading to an enhanced local immune response. Presumably this would be of value in helping the body to deal with any foreign proteins that had found their way into the skin, including pathogens such as bacteria and parasites.

Julian

2006-07-07T03:29:00.000-07:00

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Is homosexuality due to genetic conflict or cooperation in the family?

I have been thinking a bit about these recent results that indicate a markedly higher rate of homosexuality in boys with older brothers. I wonder if this could be seen as part of a genetic strategy on the part of males to remove their younger brothers from the breeding pool and perhaps enhance the suppport they receive in their own breeding efforts.

If male foetuses were capable of influencing intrauterine conditions for subsequent male babies in a way that tended to cause homosexual orientation, via effects on hormones and male foetal development, this could be a good genetic strategy for them in a small society. If early humans lived in small bands of a couple of hundred people [as is often suggested], the advantage of removing one's brothers from the potential breeding pool, while quite possibly having them still in the band and able to contribute to the provisioning and care of one's own young, could have been considerable.

Analogies with queen bees and their infertile worker sisters come to mind.

ADDENDUM: On further reflection, I wonder if a more likely scenario is that of parental effects. If a pregnant woman's body has a tendency to reject what it perceives as immunologically foreign in a male foetus, namely the masculine elements, this will tend to put pressure on male foetuses. Those which already have a low tendency to masculinise, for genetic or environmental reasons, may be tipped over the balance into homosexual orientation. Since an individual that is going to be less masculine in any case will probably not compete as well in the struggle for desirable mates, it might be desirable from the mother's point of view for her "to cut her losses" genetically and allow or encourage the production of a homosexual son. As noted above, in the kind of small band in which humans probably lived in prehistoric times, it might be desirable for her more masculine sons to have less competition and more help from their homosexual brothers. Having later sons homosexual is especially likely to be acceptable, because the mother already has normal sons in the population.

The argument against homosexual orientation being simply a sporadic developmental anomaly is that it seems to occur at a rather high frequency. It seems possible that its occurrence is under some kind of control. Appropriate allocation of resources (including sexual orientation) to males is particularly important because their breeding results - and hence the mother's success in passing on her genes to the next generation via her sons - are going to be much more variable than for daughters. This is because an individual male can potentially father many more children than an individual female can bear.

FURTHER ADDENDUM: Mother birds vary the amount of the sex hormone precursor, androstenedione, that they provide to their young depending on the life history typical of the species, according to this report:

"In birds, mothers pass androgens [male hormones] to their eggs, and these hormones have been shown to influence the development and behavior of nestlings."

Julian

2006-05-14T01:13:00.000-07:00

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Scientists have emotions, just like real people

One of H G Wells' less well-known short stories is "The Moth", about the hatred that develops between two entomologists. The hatred in the story began when one scientist "extinguished a new species" created by the other. That is, he wrote a paper claiming that a supposedly new species was only something that had already been described.

The latest issue - Volume 6 - of "Calodema", the "journal devoted to promoting knowledge about the flora and fauna of Australia and the Pacific" has a paper that reminded me of the H G Wells short story. Dr Dewanand Makhan has written an indignant article in which he forcefully restates his view that three Chinese water beetle types that he has studied really are new species, and not merely specimens of already known species. Dr Makhan supplies drawings and photomicrographs to support his case. He has also made some further observations that he says show that his species are truly novel finds. I am no expert, but he seems to have made his case. Of each water beetle, he writes that it is "hereby reinstated as a full and distinct species".

As H G Wells meant to show in his short story, scientific scholarship is not immune from strong emotion.

Dr Makhan has contributed another paper to Volume 6 of "Calodema", on another of his fields of interest, jumping spiders (Salticidae) from Suriname in South America. Also on the topic of spiders, there is a book review by Englishman Maurice Pledger of Dr Trevor Hawkeswood's "Spiders of Australia". Trevor (spilopyra@hotmail.com) is the Editor of "Calodema" and a prolific field biologist with an international reputation. As Pledger notes in his fulsome review, this book on Australian spiders is an especially good guide because it includes so many original observations and conveys the inspiring message that research on Australia's natural history remains an exciting work-in-progress.

Other papers in this issue of "Calodema" cover a variety of taxa and topics: a description of the pupa of a stag beetle from Queensland; notes on a beetle that lives in dead individuals of the distinctive "grass trees" of Australia; more on Trevor Hawkeswood's signature group - the jewel beetles; extensive butterfly checklists provided by Kelvyn Dunn from Australian National Parks, including the very rich Iron Range National Park of Cape York Peninsula; and a herpetological survey of an ecologically degraded area of New South Wales.

Most people interested in natural history are interested in the Australian zone. "Calodema" is a rich source of relevant material, especially for those with a more than casual interest.

Julian

2006-03-13T14:25:00.000-08:00

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Colour vision and sexual signalling in primates, including humans

From a Caltech press release:

QUOTE

In fact, trichromat vision is sensitive not only for the perception of these subtle changes in color, but also for the perception of the absence or presence of blood. As a result, primates with trichromat vision are not only able to tell if a potential partner is having a rush of emotion due to the anticipation of mating, but also if an enemy's blood has drained out of his face due to fear.

"Also, ecologically, when you're more oxygenated, you're in better shape," Changizi adds, explaining that a naturally rosy complexion might be a positive thing for purposes of courtship.

Adding to the confidence of the hypothesis is the fact that the old-world trichromats tend to be bare-faced and bare-butted as well. "There's no sense in being able to see the slight color variations in skin if you can't see the skin," Changizi says. "And what we find is that the trichromats have bare spots on their faces, while the dichromats have furry faces."

"This could connect up with why we're the 'naked ape,'" he concludes. The few human spots that are not capable of signaling, because they are in secluded regions, tend to be hairy-such as the top of the head, the armpits, and the crotch. And when the groin occasionally does tend to exhibit bare skin, it occurs in circumstances in which a potential mate may be able to see that region.

"Our speculation is that the newly bare spots are for color signaling."

UNQUOTE

A weakness in this theory is that early humans - being Africans - presumably had black skin. One of the few exceptions seen in modern Africans are the pink mucous membranes made visible by the characteristic eversion of the lips in many Africans. I discuss the possible role of these pink lips in signalling health here. I presented this idea to a recent annual meeting of the Australasian Society for Human Biology.

Julian

2006-01-21T02:15:00.000-08:00

Another fine issue of "Calodema"

Trevor Hawkeswood keeps up a high standard with his latest issue of "Calodema", "An Australian biological journal devoted to promoting knowledge about the flora and fauna of Australia and the Pacific". Volume 4, with the now familiar cover illustration of the magnificent Australian jewel beetle, Calodema regale, includes some observations that will intrigue anyone interested in natural history.

Of particular importance is the report by Trevor of two new populations of the rare plant Zieria involucrata. This shrub is listed under the New South Wales Threatened Species Conservation Act (1995) as "Endangered", according to the recently issued popular book, "Seldom Seen: Rare Plants of Greater Sydney" by Alan Fairley (published by Reed New Holland in 2004). Fairley's book contains some useful background on this plant and an illustration of the "large flowerheads and softly hairy leaves" typical of the species. Dr Hawkeswood reports two populations of 25 and 10 individuals respectively in the rugged sandstone ridgetop habitat within the Lower Portland area of north-western Sydney. The exact locality is kept secret for the safety of the species. Trevor discusses the conservation status of the plant.

Dr Dewanand Makhan continues his work on new species, particularly water beetles and particularly from Suriname in South America. Also included is his report of three new jumping spiders (Salticidae) from the same country.

Other papers included in this issue of Calodema cover a specialty of Dr Hawkeswood's, namely studies on beetle host plants, both of the larvae and adults.

Paul O Downey is listed as a specialist on parasitic plant species. It seems he works at the Cooperative Research Centre for Weed Management Systems here in Australia. He recently (1998) published an inventory of host species for aerial mistletoe species in Australia. Trevor Hawkeswood cites this inventory in two papers in the latest Calodema on observations on Australian native mistletoes parasitising introduced trees, namely a pear tree and - most extraordinarily - the London plane tree (Platanus). Trevor suggests that, with the decline of eucalypts (the usual host of the Australian mistletoe, Dendrophthoe vitellina) in the area of observation, the parasitic plant appears to be broadening its host range in order to survive. All sixteen London plane trees in the main street of Riverstone, New South Wales, were observed to be heavily parasitised. The mistletoe was not apparently having any serious effects on the host.

My only complaint about this issue is that it lacks the usual index.

Dr Trevor Hawkeswood, the Editor of "Calodema", can be contacted at the following email address: spilopyra@hotmail.com

Julian

2005-12-29T20:41:00.000-08:00

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O'Dea J. D. (2006). Did Conflict Between Chromosomes Drive the Evolution of Sex? Calodema, 8: 33-34.

Did Conflict Between Chromosomes Drive the Evolution of Sex?

J.D. O'Dea
Visiting Fellow, School of Botany and Zoology, Australian National University

One of the most prominent of the many theories on why sex evolved is that it provides constant genetic recombination, which will allow more rapid evolution of new types of parasite resistance (Hamilton et al., 1990). Hamilton was thinking about multicellular parasites such as worms. But genetic elements such as chromosomes can also be parasitic and conflict within the genome is currently a hot topic in biology (Burt and Trivers, 2006). Putting some of these thoughts together, I propose that sex might have evolved to rid cells of worthless ("parasitic") genetic material.

Imagine a primitive cell with some good chromosomes and some ineffective chromosomes (that is, genetic material that is not advantageous to the cell but is merely "along for the ride"). How are the other chromosomes to solve this "free rider" problem? Suppose the effective chromosomes act together to override the ineffective chromosomes and force a process of recombination (that is, sex). If a new generation of cells end up with nothing but effective chromosomes, they will tend to proliferate more effectively than the older generation. Cells which contain mostly good chromosomes with one or two parasitic genetic elements or chromosomes and end up, after recombination, with a new small set of undesirable chromosomes are no worse off and will proliferate as quickly as before. But new generation cells that are the result of recombination events that result in a concentration of undesirable genetic elements or chromosomes may proliferate poorly or even die. The net effect: a "cleansing" of undesirable genetic elements, resulting from what is effectively a "warfare" between chromosomes.

This is not a "group selection" proposal. It merely requires "good" chromosomes to act in concert to override a smaller number of parasitic chromosomes to force recombination (sex), which could result in the effective expunging of the parasitic, non-contributing genetic material.

That is, sex may have evolved as a mechanism resulting from intragenomal conflict.

This suggestion in some ways resembles that of Kondrashov (1988), except that it places the emphasis not on competition between individuals but on competition between chromosomes or genetic material: that is, on intragenomic conflict. Also, the present suggestion might apply to the initial evolution of sex: other functions (such as that suggested by Hamilton in relation to resistance to parasites) might have helped maintain it once it had evolved in the first place.

A calculation:

It is possible to calculate how advantageous it would be to a functional chromosome to have the cell in which it resides (along with a parasitic non-functional chromosome) recombine with another similar cell. If one assumes (for the sake of calculation) that both cells contain three functional chromosomes and one parasitic chromosome, the following are the results to be expected from sexual recombination of the chromosomes - with two new cells resulting from the random mutual exchange of half of their chromosomes (that is two from each cell):

For a functional chromosome, following recombination, there are 6/18 chances of an improvement in its situation (that is ending up in a cell with fewer parasitic chromosomes). There are 9/18 chances of no change (ending up in a cell with the same number of parasitic chromosomes). And there are 3/18 chances of ending up in a new cell with more parasitic chromosomes. In short, recombination provides a greater chance of ending up in a healthier cell than in a less healthy cell - that is, of ending up in a cell with less parasitic, useless genetic material (parasitic chromosomes).

In contrast, for a parasitic chromosome, recombination will never improve its situation. There is a 9/18 chance of no change and a 9/18 chance of actually ending up in a new cell with a higher level of parasitic material. Such a cell is likely to be less viable and may even die, destroying the original parasitic chromosome with it.

In conclusion, it will have been to the advantage of normal, functioning chromosomes to code for and promote sexual recombination with other cells. Therefore, sex will have evolved.

Burt, A. and Trivers, R. (2006) Genes in Conflict: The Biology of Selfish Genetic Elements. The Belknap Press of Harvard University Press, Cambridge, Massachusetts and London, England.

Hamilton, W. D. et al. (1990) "Sexual reproduction as an adaptation to resist parasites". Proceedings of the National Academy of Sciences (PNAS) 87:3566-3573.

Kondrashov, A. S. (1988) "Deleterious mutations and the evolution of sexual reproduction". Nature 336:435-440.

An updated, clearer version of this paper can be found at:

http://julianodea.blogspot.com/2011/11/selfish-chromosome-why-sex-evolved-by.html

2005-12-16T01:15:00.000-08:00

Ancient heroes and their Y chromosomes

Steve Sailer writes about some Irish and Scots mediaeval patriarchs and the remarkable number of their descendants. (He also mentions the case of Genghis Khan, who apparently had a huge number of descendants sharing his Y chromosome.) The implication is that these mediaeval patriarchs, one of whom gave his name to the Irish O'Neill family, were extraordinarily fecund.

I wonder if another way of looking at the success of these lineages is to consider that they may have been not so much unusually fecund, but geographically mobile. Genghis Khan certainly got around, ranging widely across Asia. Suppose he left sons all over this area, and they settled widely, attracting women to be with them. They could become locally dominant simply because they were settling relatively empty areas. That is, we might be dealing with a kind of "founder effect".

The Scots and Irish cases are somewhat similar, in that the locally dominant surnames and Y chromosomes are associated with out-of-the-way areas that might have been settled relatively late - Northwestern Ireland in one case and the Western Islands and Highlands of Scotland in the other.

Have a man settle a large new territory; breed several sons; let them take wives from outside on their travels and settle back in the large new territory. You would have plenty of space to live and breed, some initial outbreeding to avoid inbreeding, and the makings of a very prevalent Y chromosome. That is, the original man with the Y chromosome would not have had to be particularly fecund, provided his sons and grandsons were colonising a large new area.

Julian

2005-11-26T23:10:00.000-08:00

Calodema No. 3

I recently received the third issue of "Calodema", a natural history journal edited by a friend of mine, Trevor Hawkeswood. Trevor is a prolific field biologist, whose main areas of interest are botany and entomology. "Calodema" is his journal "dedicated to promoting knowledge about the flora and fauna of Australia and the Pacific". Why "Calodema"? Because, as the cover photo shows, Calodema regale is a magnificent Australian jewel beetle. Jewel beetles (Buprestidae) are one of Trevor's special interests. Anyway, what's in the latest issue? A surprising range of topics. The issue opens with a complaint about the poor quality of citation in a paper on the host plants of an economically important Australian longicorn beetle, Agrianome spinicollis. Trevor's theme is that Australian biology journals are not edited with all due care. Returning to jewel beetles, the next article has some fascinating photos - of male jewel beetles fascinated by beer bottles. Biologists interested in animal behaviour have long known about "supernormal releasers": these are artificially enhanced versions of normal stimulators of behaviour. For example, a bird may prefer to sit on a larger, fake version of a normal egg, if it is the right colour and pattern. A supernormal stimulus can behaviourally "overstimulate" an animal. In the case discussed in Calodema, beer bottles discarded in the bush have just the right brown colour, and stippled pattern, to closely resemble the colour and pattern of females of the species. Males waste their time courting beer bottles instead of female beetles.

Dr Dewanand Makhan, of the University of Utrecht in The Netherlands, continues his descriptions of new beetles in the next article, with four new species from China. The new species are in the family Scydmaenidae, relatives of the more familiar rove beetles (Staphylinidae). Here is a fossil member of the family Scydmaenidae in amber. Dr Makhan has named one of the new species after Trevor Hawkeswood, "world renowned entomologist and environmental scientist from Australia". In another paper in this issue of Calodema, Dr Makhan continues his previous work on new species of water beetles (Hydrophilidae), from Suriname in South America in this case. Perhaps his Dutch hosts have a special connection to what used to be a Dutch colony.

Two further articles follow up on another of Trevor's themes: the way in which Australian natural history information becomes lost. In a sparsely populated country like Australia, when it comes to researching the flora and fauna "the harvest is rich, but the laborers are few", to use a biblical reference. This is made worse by the tendency for what knowledge is gleaned to be lost. Trevor refers to two books: "Bush Rambles" by AG Hamilton (1937) and "Our Dying Fauna" by AM Douglas (1980), which contain interesting Australian natural history information which has been largely forgotten or ignored. I am often amused by the contrast between England and Australia in this regard. In the "mother country", the fauna and flora are very well-known. The discovery of a new species there would be - almost - headline news. In Australia, the diversity overwhelms the naturalist. Often, he doesn't know where to begin. There is plenty to study, but resources in the form of guidebooks, for example, are relatively sparse. I remember being told, when I was studying entomology at the Australian National University, not to worry too much about exact identification of anything we collected because "it might be a new species". That's the wonder of Australia, and the problem for the student.

I am not quite sure what to make of the next two articles in the journal, accounts by Kelvyn Dunn of his experiences of being bitten by a wasp in Samoa and a spider in Australia. The accounts are certainly written with verve, even if they do contain sentences that begin "Under masculinity alignment, some social de-constructionists might argue ..." It is always enjoyable to read of others' bad experiences "in the jungle", and the toxicologist in me was intrigued by the accounts of the effects of the bites and stings. I even went out and bought a book on bites and stings to help follow what was going on. However the second of Kelvyn's articles raises doubts about whether he was really bitten by a white-tailed spider, as surmised in the first paper, or by something else. The white-tailed spider, Lampona cylindrata, acquired a sinister reputation in Australia a few years ago for the nasty, lingering symptoms associated with its bite. More recently, doubts have arisen about whether the white-tailed spider really deserves its reputation. I need to research the topic more before attempting to comment further on Mr Dunn's articles. They are a really good read, though. He sounds like a great bloke. (I recently met a young man who met and married a Russian girl from Moscow. What, I asked, did she like most about Australia, and what the least? I was told that she liked everything about Australia, except the spiders.)

Calodema No. 3 ends with a copy of my review of Calodema No. 2.

Julian

2005-09-01T05:36:00.000-07:00

Another TV show about Hobbits, Homo floresiensis

The ABC, here in Australia, showed a documentary recently on the "Hobbit" fossils from Indonesia. The thrust of the program was that the Hobbits, Homo floresiensis, were Homo erectus that experienced "island dwarfing" down to a tiny size. There was much "messing about in boats", or rather a bamboo raft, in the documentary, allegedly to show that Homo erectus could have crossed to Flores Island, where the Hobbits lived. Skulls of Homo erectus were compared to Homo floresiensis, and it was claimed that the latter resembled a much reduced version of the former.

The "island dwarfing" was supposedly due to a shortage of food on Flores, which also led apparently to smaller size in the local species of elephant.

Villagers on Flores told a story of how tiny Hobbit-like humans used to live on a nearby mountain until conflict with the villagers led to their demise a few generations ago.

I found none of this particularly impressive. Bamboo rafts seemed merely a diversion. To assign the small size of a hominid on Flores to "island dwarfing" seems to depend on an argument that Flores is a small island (it isn't); that there were few resources (despite the existence of rats, giant lizards and elephants); and that humans typically get small on islands (they don't). Also, why did a supposed shortage of resources produce small elephants but giant lizards?

When the Hobbits were recreated on the screen, their environment was shown as heavily forested. This is consistent with suggestions that the palaeoenvironment was in fact rainforest.

Here is my take on the situation. Evidence suggests that hominids, either Hobbits or their ancestors, lived on Flores over about 80,000 years until about 20,000 years ago. During this time they used a modern human toolkit. My proposal would be that they reached Flores as archaic Homo sapiens, the skulls of which bear some resemblance to the Hobbits in overall form. Under long selective pressure in a rainforest environment, they developed the typical traits of modern humans in that environment, notably dwarfism (Cf. Pygmies, Negritos). The force and duration of the selective pressure led to an extreme pygmoid type, which included diminution of the entire skeleton including the skull. The brain was "packed" with great efficiency, permitting normal intelligence despite a very small brain size, the use of a modern human tool kit and modern hunting capabilities.

Julian

2005-07-15T19:16:00.000-07:00

Did horror writer HP Lovecraft have acromegaly?

Here is a picture of him as an adult.

For comparison, here is a picture of him as a child.

More pictures and a biography here.

Acromegaly seems possible. Does anyone know?

Steve Sailer has suggested that John Kerry may have had acromegaly. This article includes a picture of John Kerry from his college days. Other famous cases of acromegaly have been Primo Carnera, the boxer, and the people discussed here.

There is a good chapter on Primo Carnera in this book by Harold Klawans, the neurologist and writer.

Julian

2005-07-04T00:12:00.000-07:00

Rainbow effects in parrots' plumage

I have sometimes wondered why it is that scarlet macaws show the colours of the rainbow in order. That is, not only does this parrot have "all the colours of the rainbow" but they are in the same order on the body of the bird as the colours in a rainbow. It suggests some kind of structural cause for the coloration rather than individual pigments that just happen to be present in the bird's plumage in the order of a rainbow: red, orange, yellow, green, blue ...

This paper "The Chemical Structure of the Pigments in Ara macao Plumage" by Stradi et al. suggests that something structural is indeed going on. Note this quote:" We expect to demonstrate that the brilliant colors of the parrot plumage are principally due to such interactions, and that parrots construct their rainbow of color simply by modulating the interaction of a few endogenous yellow pigments with the plumage keratin. " That is, there may be a single basic pigment that is converted "structurally" to produce other colours. What is interesting is that the structural modulation seems to vary in such a way that the plumage shades change in the same order as a rainbow, at least in the case of Ara macao, the scarlet macaw.

I noticed today, at the Canberra Zoo and Aquarium, that the sun conure (another parrot) has a somewhat similar pattern of colours as the scarlet macaw, with the colours of the rainbow in rough order, with the reds, oranges and yellows at the top of the bird and the greens and blues on the wings. This conure is probably fairly closely related to the macaws.

Julian

2005-07-03T17:37:00.000-07:00

The Lyon hypothesis and the maintenance of pregnancy

The Lyon hypothesisis the suggestion that female mammals, including women, have one of their two X chromosomes randomly inactivated in each cell. I wonder if this is related to the need for female mammals to carry offspring inside their bodies during pregnancy but not reject them as immunologically different. If the female is herself a genetic mosaic, she may be more tolerant of a wider range of immune types in her foetus.

This article may be relevant.

Julian

2005-06-16T04:06:00.000-07:00

The value of theorising in biology

Sometimes I wonder about the value of what I try to do here and in some of the papers I have published. But I found this from the Gene Expression blog to be a very good defence of the value of theorising in biology.

Julian

2005-06-14T01:20:00.000-07:00

Yes, Flores is really quite a big island

Some evidence and remarks at John Hawks anthropology blog, which tend to support my argument that "island dwarfing" does not really explain the small size of the "hobbits" (Homo floresiensis) who used to live there. The media uncritically repeated the line that the tiny size of these hominids was due to "island dwarfing". This was despite the fact that the island where the early human bones were found (Flores) is over two hundred miles long. Don't journalists have atlases any more?

More on "island dwarfing" from John Hawks here.

Julian

2005-06-06T05:27:00.000-07:00

"Mad as a Meat Ant"

This paper "Dietary fats and body lipid composition in relation to hibernation in free-ranging echidnas" by Falkenstein et al. has, I think, solved an old puzzle for me. Years ago I noticed that our housecats were very excited and pleased by the scent of crushed meat ants (Iridomyrmex) on my boots. I assumed that there was something in the ants' bodies that "turned on" cats, and I actually did some experiments with formic acid, without success. I found the Falkenstein paper recently, which mentions the abundance of oleic acid in meat ant bodies. I also found out very recently that oleic acid is one of the important constituents of the pheromone that cats wipe on objects with their chins. It is possible to buy a synthetic mixture of fatty acids - including mostly oleic acid - which can be sprayed around a home to comfort cats and improve their behaviour in various ways. So - I now surmise that what my cats were reacting to so delightedly was the oleic acid released by the crushed meat ants.

Julian

2005-05-25T02:30:00.000-07:00

Why were Tasmanian Aborigines Dark-Skinned?

Scientists, especially those who live in the Northern Hemisphere, often suggest that it is anomalous that the Tasmanian Aborigines were dark-skinned. Here is an example from the prominent Gene Expression blog:

QUOTE

" One point people bring up is the relative darkness of Australian Aboriginals even though much of the continent is in the "temperate" zone. It could be fairness (or the genetic variants that result in it) is not in the "genetic" background of this population, but blondeness among Aboriginals of the deep desert seems to falsify this thesis, and one supposes that the original populations that exited northeast Africa were also rather small and lacking in genetic diversity. But, Australia is mostly dry, and so rather sunny, in comparison to Europe. Only Victoria is really in a temperate maratime climate. And, to my knowledge, no group of Aboriginals wore very much clothing.

A more interesting case is that of Tasmanian Aboriginals. This group, now extinct in an un-admixed state, was very dark skinned, and had been isolated on Tasmania for about 10,000 years. Tasmania does have a cool maratime climate like much of Europe. My impression is that Tasmania aboriginals were not totally naked. "

UNQUOTE

My comments on this are as follows. Australia straddles the Tropic of Capricorn, so Australia is only partly a temperate zone country. Tasmania itself is at the same latitude in the South as Corsica is in the North. It is not that far South, really. It has a mild climate. Why did the Tasmanian Aborigines have dark skin? Well, one reason, as I've already indicated, is that Tasmania is fairly sunny. It is certainly not Norway, or even Vermont. It is hard to be certain, but some early accounts suggest that the Tasmanian Aborigines did not wear a lot of clothing. Another point is that they were hunter-gatherers, with access to meat and seafood, which could have provided good sources of vitamin D. Oddly enough, there seemed to be a taboo on fish, but they certainly ate seals, seabirds and shellfish. Many of the tribes would have had access to such coastal resources.

In summary, the dark skin of Tasmanian Aborigines is something of a puzzle, but there are some possible explanations that can be fitted into the usual model of human skin colour that relates skin colour to the local levels of sunshine and other sources of vitamin D.

2005-05-23T02:31:00.000-07:00

Moloch horridus

David Attenborough has narrated a documentary on lizards. What I saw of the documentary focussed on the lizards known as "dragons", Agamidae, which are mostly found in Australia. In particular there was a sequence on Moloch horridus, the Thorny Devil.

Both this website and Attenborough refer to the curious forwards-backwards shaking movement the lizard makes as it moves slowly along. That is, it rocks backwards and forwards as it walks. Both the website and Attenborough imply that this is a kind of camouflage or cryptic movement, to help the lizard resemble swaying vegetation. The Thorny Devil is a prey item as well as a predator and it is conjectured that the rocking movements help its camouflage.

Other animals that make similar rocking movements as they walk include some chameleon lizards, if I recall correctly, as well as many stick insects and praying mantises. In the case of these insects, a cryptic resemblance to swaying vegetation has also been proposed.

On the other hand, as I proposed in a paper some years ago in an entomological journal, the rocking movements made by these large, typically arboreal insects may actually be to aid in achieving vision. By moving their body (and therefore their eyes) backwards and forwards the animal can detect objects and gauge their distance from the objects' parallax movement against the background. This would be particularly valuable for animals with comparatively simple vision that do not move quickly and freely enough to generate relative motion - and therefore parallax movement in the visual field - in any other way. That is, rocking movements among these insects are a way of obtaining visual information when the whole animal is not able to move freely and quickly.

What applies in the case of these large, slow-moving arboreal insects may also apply to the slow-moving Thorny Devil. That is, the rocking movements of the lizard may be to help the Thorny Devil see objects, not to help it resemble swaying vegetation.

2005-05-22T02:58:00.000-07:00

Yet another claim that honey bees have a language

More "science by media release" yesterday, with the announcement that scientists in England had claimed proof that bees do indeed use dance language to communicate where nectar is. This language theory was developed first by Karl von Frisch and won him a Nobel Prize. However, Adrian Wenner continues to be sceptical of the hypothesis and the new results that supposedly confirm it. I like the picture of the bee with its tiny radar reflector attached in the news report, but I remain to be convinced, especially as several supposed "final proofs" of the reality of the dance language have appeared in recent years. I hope to review the new data soon.

What troubles me about the dance language hypothesis is that it seems to change slightly all the time and the supportive data always seem a bit marginal. Note the following phrase from this report: "Only two of the bees in the first experiment ever actually found the food source, Riley conceded ..."

I have published my own critique of the dance language hypothesis, from an evolutionary point of view, here.

2005-05-22T02:54:00.000-07:00

Further musings on Hobbits (Homo floresiensis)

Now that their Indonesian captivity is over, the world can look forward to more science being done on the Hobbit bones. In the meantime, here are some results:

" 'Hobbit was a smart little human` say scientists " " The overall shape of the hominid’s brain is very similar to that of Homo erectus (an earlier ancestor of modern humans). It also has some very advanced features that compare well with the modern human’s brain. Particularly, the frontal lobe, the temporal lobes at the sides and at the back of the brain are very similar to a modern human brain’s features. "

When I was at the Australasian Society for Human Biology meeting last December, I made two remarks in a comment from the floor. One was that I thought the Hobbit could be an extreme form of pygmoid Homo sapiens, associated with rainforest palaeoenvironment. I discuss this further in a post below. The other was that bird brains are very small but some birds (crows, parrots) are being found to be remarkably intelligent. I speculated that a small, well-packed human brain could likewise be intelligent. It seems I was on the right track. (I saw a small flock of sulphur-crested cockatoos feeding on pinecones today. Some were eating them in the tree; some were eating them on the ground. The latter had them upright on the ground and were munching away contentedly. Beautiful big birds - quite "confiding" as birdlovers say - and behaving as intelligently as any monkey with a piece of fruit.)

An interesting thing about the Hobbit find is that two developments have been typical of the aftermath of a major new find of ancient man. One is the bitter dispute over ownership of the material. The second is the claim that the bones are really just from a diseased individual (a microcephalic in this case).

I am constantly surprised by the claim that Homo floresiensis must have been a result of "small island dwarfing". Get out the atlas, and check the island of Flores. It is over two hundred miles long. A "small island"?? Moreover, if islands tend to cause human dwarfing, someone should tell that to the Samoans, the biggest people in the world.

2005-05-22T02:50:00.000-07:00

Ricin

Duncan Campbell writes in The Guardian (UK) that: " ... ricin is not a weapon of mass destruction. It is a poison which has only ever been used for one-on-one killings and attempted killings. " On the other hand, the US Armed Forces Nuclear, Biological and Chemical Survival Manual states that: "Acute lung injury in large numbers of geographically clustered patients suggests exposure to aerosolized ricin." which suggests that ricin could be used as a biological weapon.

2005-05-22T02:47:00.000-07:00

Cuckoldry not that common after all?

Claims that covert non-paternity (the putative father not being the actual father of a child) is as high as 10% in human populations have been common in recent years. Some time ago, I noticed that there was a discrepancy between this claim and studies done on the inheritance of surnames, which seemed to imply a much lower rate of non-paternity. If 10% of births in the typical family in the past were not actually the children of the father, it is easy to see that, after several generations, the relationship between a surname and the y-chromosome (that is, the actual paternal line) will become rapidly more tenuous. If 10% of "sons" of fathers, taking their father's surname, are actually another man's (the result of adultery), after seven generations less than half the surnames will accurately reflect the true male line [0.9 x 0.9 x 0.9 x 0.9 x 0.9 x 0.9 x 0.9 = 0.48 = 48 percent]. And yet there are studies, such as the Sykes surname study (cited here), extending over many past generations (700 years), which imply much lower rates of non-paternity (1.3% per generation in the Sykes case).

This recent study by Kermyt G. Anderson of the Department of Anthropology, University of Oklahoma, seems to imply that the lower figures for non-paternity are more probable:

" The results suggest that men with high paternity confidence are generally correct in their paternity assessment; these men overwhelmingly tend to be the actual genetic fathers of their putative children, with a median nonpaternity rate of only 1.9%. If men with high and unknown levels of paternity confidence are combined, the median nonpaternity increases to only 3.9%. These figures are dramatically less than the “typical” nonpaternity rate of 10% or higher cited by many authors (e.g., Alfred 2002, Cervino and Hill 2000, MacIntyre and Sooman 1991, Stewart 1989), or the median worldwide nonpaternity of 9% reported by Baker and Bellis (1995). These results presented here suggest that men who think they are the fathers of their children actually are the fathers between 96.1 - 98.1% of the time. "

The Sykes surname study has always seemed like powerful supporting evidence for a low rate of human cuckoldry. I have discussed this with various evolutionary psychologists on the Internet, and some have suggested that morals and behaviour have changed rapidly in recent years. That is, they have suggested that, whereas the Sykes study reflects stricter past behaviour, modern cultures around the world are more "free and easy" and 10% non-paternity is likely in their case. However, this new study from the University of Oklahoma implies that modern cultures are not more "free and easy".

To my mind, surname studies like the Sykes study have all along been very hard to explain if one believes in high (10%, for example) rates of cuckoldry (non-paternity) among humans. It is increasingly likely that what the Sykes study implies is accurate: that ordinary Englishmen and Englishwomen were, on the whole, remarkably well-behaved over a remarkably long time: "When all is said and done, there is more said than done." Despite the occasional shenanigans that undoubtedly went on, and that gave us so many colourful English expressions (like "cuckoldry"), the general picture is of a remarkably high standard of behaviour in an ordinary English population.

2005-05-22T02:43:00.000-07:00

Hobbits and Pygmies

Last year, at the annual meeting of the Australasian Society for Human Biology, I suggested from the floor that the Flores "hobbits", Homo floresiensis, might have been simply very extreme Pygmy humans. This has been presented as fitting in with the idea that the hobbits were really pygmoid.

Apparently the contemporary "pygmies" on Flores live in an area of dense forest in central Flores, according to this report. Modern Pygmies and Negritos are found in rainforest, and their body size seems to be adaptation to this environment. There are "Negritos" all through south east Asia, so it is not really surprising that some have turned up on Flores.

I don't think that the hobbit skeletal material can simply be referred back to this modern Negrito population. Apart from anything else, the hobbit's tiny skullsize and extremely short stature are unlike the modern Negritos who have recently been found on Flores. I suspect that the hobbit was an individual from a group of ancient rainforest-adapted people who were even shorter than modern Pygmies and Negritos, and whose anatomy, including their tiny skulls, was an adaptation to the rainforest environment of a different and more extreme type than is found in any modern group.

2004-10-28T06:21:00.000-07:00

Why were the "Hobbits" of Flores so small?

Just a quick note now on the newly-discovered extinct humanlike species, Homo floresiensis, which I may flesh out further later.

This discovery of tiny human skeletons on the island of Flores in the Indonesian archipelago, dated to 18,000 years old, has cause immense excitement. I was particularly interested in the question of why these people might have been so tiny, only a metre tall.

There have been suggestions that living on a small island, with not much food, could have led these hominids to become very dwarfed. I have two problems with this: one is that Flores is not really a small island, and the other is that, if the people were hunting elephants and so on, shortage of food is not obvious. Ten years ago I published a theory (in the journal Homo, published in Stuttgart in Germany, Vol. 44/3, pp. 284-7) to attempt to explain the short stature of the Pygmies and Negritos of the rainforests of Africa and Asia. Basically, I argued that the dense rainforest canopy reduced the amount of ultraviolet light available to the forest-dwellers; which reduced the capacity for making vitamin D in the skin; which reduced the ability to take up calcium for the skeleton; which made having a small, slow-growing skeleton a good thing. Hence, the small skeleton (and body, of course) of Pygmies and Negritos.

Here is a description of the likely environment of the Flores people:

" We don't know much about the paleoenvironment on Flores yet, but everything's consistent with it being heavily rainforested back in the Pleistocene and probably heavily rainforested until agricultural humans arrived and started clearing the rainforest. "

So, it is possible that the Flores "Hobbits" lived in rainforest, and my theory on why rainforest people become dwarfed could apply to them as well. Perhaps they lived there a very long time, and became correspondingly very small. That is, they evolved very small skeletons to avoid rickets and other bone problems in an environment where there was little ultraviolet light to help make the necessary vitamin D.

Here is a short note I had published on the levels of ultraviolet light in North Queensland rainforest.

Julian

2004-05-18T20:44:00.000-07:00

Creating life using piezoelectricity

A longstanding theory on how the first molecules of life were formed is that founded on experiments that show that electrical discharges in the presence of simple organic molecules such as methane, together with ammonia and water, produce more complex molecules found in life. See the Oparin-Haldane hypothesis discussed briefly here and the Miller-Urey experiment discussion here.

The usual form of electrical discharge considered is lightning, but it occurred to me recently that there is another natural source of electricity - the piezoelectric effect. In the piezoelectric effect, pressure on crystalline matter, such as that in rocks, produces an electric current.

The piezoelectric effect seems particularly interesting because of recent suggestions that life (bacteria for example) is common deep in the crust of the earth and that it might even have evolved there:

" The rocks that have hydrogen, methane and other fluids percolating upwards would seem to be the most favorable locations for the first generation of self-replicating systems (9). Deep in the rocks the temperature, pressure, and chemical surroundings are constant for geologically long periods of time and, therefore, no rapid response to changing circumstances is needed. Ionizing radiations are low and unchanging. No defense is needed against all the photochemical changes induced by ultraviolet light or even by the broad spectrum of visible sunlight.

Bacteriologists have speculated that since a large sub-group of archaebacteria - the most primitive and judged to be the most ancient bacteria - are thermophiles, this may indicate that primitive life evolved at such high temperatures in the first place (10). If it did, and if the archaebacteria are the earliest forms of bacteria, evolved at some depth in the rocks, they may have spread laterally at depth, and they may have evolved and progressed upwards to survive at lower temperatures nearer the surface. Some combination of lateral spread at depth and spread over the surface with subsequent re-adaptation to the conditions at depth will have allowed them to populate all the deep areas that provided suitable conditions to support such life. "

What else is likely deep in the crust? - piezoelectricity.

I haven't found any references to this possibility, but it does seem to me that electrical charges acting on methane, ammonia and water (all found beneath the earth) could have helped form the building blocks necessary for life on Earth (such as amino acids) deep in the Earth's crust.

I have found this, however. In a discussion of the possibility of life on Europa, one of the moons of Jupiter, this suggestion is canvassed:

" Also, this heating mechanism and the cracks in the icy surface are almost for certain caused by the huge tidal forces to which Europa is subjected because of its proximity with the giant planet Jupiter. Europa is terribly deformed by tidal forces and get regularly elongated and roundish again. This could perhaps suffice so that piezoelectric discharges exist at the ocean's solid floor and may help create the complex molecules and aminoacid the way Miller proposed. "

I wonder if the effect proposed to occur on Europa - piezoelectric discharges producing amino acids from simpler compounds - could not also have happened deep in the crust of Planet Earth.

Some authorities refer to electrical currents in the earth's crust. For example, Edward Bryant in "Natural Hazards", Cambridge University Press, second edition, 2005 writes that "Electrical currents, termed telluric currents (or Earth currents), are ... continually flowing through the Earth's crust." Here is a bit more on telluric currents and some (Australian) "back yard observations" are here. Telluric currents are not piezoelectric effects, but are caused by such things as changes in the Earth's magnetic field.

Julian

2004-04-29T17:19:00.000-07:00

African Lips As Health Signals

J.D. O’Dea, Visiting Fellow, School of Botany and Zoology, Australian National University, Canberra, Australia.

Human lips vary in the extent to which they are rolled up to expose the pink membranous portion, a phenomenon known as lip eversion.

Lip eversion has been described as particularly a trait of Africans, involving outrolling and exposure of the mucus membrane of the mouth and thickening of the lips making them stand forward from the teeth (1). The preponderance of the trait in Africa has not been explained, although it has been noted that lip eversion is a warm and/or moist climate trait (1). In line with this observation, it has been suggested (2) that everted lips may have some cooling capacity because capillaries run very close to their surface and the slight moistness of the lips could help in cooling by evaporation. However any cooling effect seems likely to be minimal.

The question of why many Africans have everted lips with visible pink mucus membranes could also be approached from a sexual signalling perspective. It has been suggested (3) that the pink lips of the human female mimic the pink labia of her vulva, and noted that “…during intense sexual arousal, both the lips of the mouth and the genital labia become swollen and deeper in colour, so that they not only look alike, but also change in the same way in sexual excitement.” It might therefore be argued that the eversion of African lips to reveal some pink surface would be necessary to achieve this resemblance. On the other hand, such an hypothesis would not explain why supposedly labia-mimicking lips occur in men and children (4).

Some anatomical features are thought to have evolved as fitness indicators that signal freedom from parasites (5). For example, the uakari monkey’s bright red face may have evolved to indicate that it is not infected by blood parasites, such as malaria, that would cause anemic pallor (6).

In lighter-skinned humans, cheeks and lips vary in color depending on the amount of blood they receive, turning pale or bluish when the blood vessels narrow in reaction to cold, ill health, or other stresses, thereby serving as potential signals of health and fitness. This situation has been compared (4) to what are believed to be similar indicators of healthy blood flow in other species such as the rooster’s comb, the turkey’s featherless head and the small patch of bare skin on the forehead of the chick of the great crested grebe.

In the darker-skinned Africans, the outer areas of the lips are dark but eversion of the lips very often reveals the inner pink mucus membrane. The vertical dimensions of the lips (the “vermilion”) vary in different ethnicities; for example, African-American males and females have 13.3 and 13.6 mm upper lip and 13.2 and 13.8 mm lower lip, respectively. North American Caucasian vermilion height norms of upper and lower lip for males and females are 8.0 and 8.7 mm and 9.3 and 9.4 mm, respectively (7). The greater height of African lips is associated with lip eversion and visibility of pink mucus membrane despite the otherwise dark skin color.

The characteristic eversion of the lips in African humans may function to make visible the pink mucus membrane so as to signal health. In the African environment, the most probable form of health and fitness being indicated would be the absence of anemia or jaundice due to diseases, including parasitic diseases such as malaria. In such disease states the exposed mucus membrane would not have its normal pink color. The capillaries running close to the surface of the lips, alluded to above, would therefore generate a clear indication of hematological health.

In summary, the characteristic eversion of African lips may have evolved to permit the display of a pink surface on the face, providing a conspicuous signal of hematological health. Non-Africans would not require everted lips, either because they have relatively fair skin on the entire face (especially on the cheeks in many Europeans) that would clearly signal hematological health or because of the lesser incidence outside Africa of diseases likely to cause jaundice and anemia.

It has been noted (1) that the lip eversion trait is not found in every part of Africa. If the proposal in this note is correct, it might be expected that the trait would be most common in areas where diseases likely to lead to anemia, such as malaria, have been most prevalent.

References

(1) Krantz, G. S. 1980. Climatic Races and Descent Groups. The Christopher Publishing House, Massachusetts.

(2) Fischer, M. (n.d.) Foundations of human culture – human morphological variation.
http://lucy.ukc.ac.uk/Courses/SE302/humanmorpohvar.html

(3) Morris, D. 1967. The naked ape. Corgi Books, London.

(4) Zahavi, A. and A. Zahavi. 1997. The handicap principle: a missing piece of Darwin’s puzzle. Oxford University Press, Oxford, New York.

(5) Hamilton, W. D. and M. Zuk. 1982. Heritable true fitness and bright birds: a role for parasites? Science 218: 384-387.

(6) Miller, G. 2001. The mating mind: how sexual choice shaped the evolution of human nature. Vintage, Random House, London.

(7) Farkas, L.G. 1981. Anthopometry of the head and face in medicine. Elsevier Science, New York.

2004-04-22T06:01:00.000-07:00

The Grace Darling Effect

Some years ago on an animal behaviour Internet discussion list we had a discussion on human bravery and the possibility of a sociobiological explanation, along the lines of kin selection and the ideas of Hamilton and Trivers.

At the time I referred to something I christened the "Grace Darling Effect". Grace Darling was a famous young heroine who helped her father row a boat out to a shipwrecked ship and rescue people. Her feat was celebrated in the eponymous poem by William Wordsworth.

At the time I wrote:

"What I am referring to is that a surprising number of heroic acts are done by teenage and younger girls.... This does not sit well with any of the sociobiological explanations that I have seen discussed. A pre-pubescent girl is unlikely to be advertising herself as altruistic to attract the opposite sex and also, I would have thought, unlikely to be indulging in misdirected altruism towards relatives. As a female who has not bred, it makes little sense for her to endanger herself. "

I later obtained information on some of the bravery awards made by the Australian Government in recent years. These will be fairly "clean" data as the stories will have been officially checked. So I am not having to rely on media reports.

The following cases have been described.

Miss Tracey Christine Gardner: "placed her own safety in jeopardy to save another teacher from possible injury."

Miss Tiani Michelle Chillemi: "fought with an armed man to save one of her parents' employees from further injury."

Miss Emily Rae Dunstan: "assisted in the rescue of her friend from the sea off Weymouth Beach."

Miss Rachelle McNiven: " rescued a boy from drowning in heavy and dangerous seas off North Narrabeen Beach."

Miss Angela Leigh Burke: "then aged 16, saved a boy under attack from a street gang of youths."

Miss Jodie Lee Parremore: "at Clifton Beach...then aged 10, placed her life at risk to save a young friend in danger."

On the basis that females described as "Miss" will be unmarried and probably childless, and in these cases the persons being protected were not relatives, these examples do not fit readily into any of the usual sociobiological categories.

Julian

2004-03-26T21:02:00.000-08:00

More on the Lynn-Flynn Effect

Steve Sailer has responded to my suggestion below to explain the Lynn-Flynn effect that there are, in his opinion, problems with the connection claimed by Levitt and Donohue between liberalised abortion laws and lower crime rates.

Here is the original paper by Levitt and Donohue that claimed that legalising abortion in America in the Seventies resulted in reduced crime rates in the Nineties.

Here is a debate between Steve Sailer and Steven Levitt. Sailer criticised the case that higher abortion rates eventually led to lower crime rates (because the potential criminals were not born).

While interesting, this debate does not necessarily invalidate my broader claims below that various developments in medical sociology will likely have reduced the number of low-IQ people being born and bred over time, and help to explain the Lynn-Flynn Effect (see my previous post).

Julian

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The Lynn-Flynn Effect

Steve Sailer, prominent writer on race and ethnicity issues, has written about the Lynn-Flynn effect:

" Perhaps the most mysterious aspect of the study of IQ is the Lynn-Flynn Effect. It was noticed as far back as the 1940s that people tended to do better on IQ tests each decade. Thus, you have to get more questions right on, say, the Wechsler IQ test to score 100 than your grandfather did because the test publisher renorms the scoring chart every so often to reflect rising performance. It is widely hoped that the Effect will lead to convergence of different ethnic groups scores toward one global average, although the evidence for this actually happening is not strong.

... we really have no idea what causes the Lynn-Flynn Effect. Lynn thinks better nutrition helps. Flynn recently offered a gene-cultural interaction theory (smart people create personal environments that exercise their brains more) that seems to me to predict divergence rather than convergence. "

As I have blogged before, it seems to me that the answer to the question should be sought at the bottom end of the scale. People often say, "If average intelligence is getting higher, why aren't we obviously smarter than our grandparents?" Well, I don't think we are. But I think we are cleverer than our great-great-uncle, who had to spend his life in a special institution because he was brain-damaged by an infectious disease as a child. That is, I think we are ignoring the most likely reason for improved average IQ - very low intelligence people aren't being born and bred in the same numbers. There are two possible reasons:

The first reason is that increasing use of contraception and abortion is removing a lot of the potential children of the very unintelligent, who would have been unintelligent themselves. Marginal Revolution has discussed this recently:

" In a very controversial paper, Steve Levitt and John Donohue provided evidence that legalized abortion in the 1970s reduced crime some 18 years later. The theory is simple. Abortion rates are higher among the poor, the unmarried, teenagers, and African Americans than among other groups and children born to mothers with several of the preceeding characteristics are at increased risk for becoming involved in crime. Legalized abortion gave these mothers an option and thus reduced the number of at-risk children who might otherwise have grown up to become criminals (note that abortion doesn't mean fewer children per-se, it may simply delay childbearing to when the mother is not poor, a teenager or unmarried which works just as well.) "

Despite these caveats, it is likely that abortion will mean fewer children in total from such women, and it is also likely that they are relatively low-IQ women. It is worth pointing out that poverty and criminality are strongly related to low IQ. More abortions mean fewer low IQ mothers producing low IQ children - which means less crime and higher average societal IQ.

So, the availability of abortion may have raised the average IQ in western societies. [This is not intended to be a moral argument in favour of abortion.]

The second reason may apply particularly to earlier decades, before abortion became so widespread. This is that fewer very low IQ children may have been born and bred as the 20th century wore on because of simple medical advances. Not just better nutrition, but greater use of antibiotics and other drugs and better understanding of conditions that can cause brain damage and low IQ: for example, meningitis, cretinism and phenylketonuria.

It seems to me that the Lynn-Flynn effect is not much of a mystery if one thinks about it in terms of the various factors that could be increasingly removing the very low IQ tail of the IQ distribution in society.

Julian

2004-03-26T20:50:00.000-08:00

The Value of Left-Handedness

It seems that left-handedness was as common in the Ice Age as now. This article suggests that:

" Left-handedness may have conferred prehistoric man advantages, such as in combat, say the researchers. "

If left-handedness did indeed confer benefit in combat, it might have been because of the "surprise value" of having to fight a left-hander. Since such a surprise value would only be effective if left-handedness were relatively uncommon, this might explain why it is found in only a quarter of the population, or less.

That is, there would seem to be an optimal level of occurrence of left-handedness. If it were too common it would lose its survival value. Some traits are like that. It is called (negative) frequency dependent selection.

The article claims that handedness is partly under genetic control. So it seems feasible to me that left-handedness is an example of a trait that is maintained in the human population because it is useful to people who have it, provided it does not become too common.

How much of an advantage is it to be a left-hander in a fight? I am not aware of any systematic studies, but people who write about boxing in America refer to "southpaw [left-hander] advantage". An example:

" And his southpaw advantage shouldn't be minimized, Ayala said.

"I know Bones has faced some southpaws, but I'm an extremely good southpaw," Ayala said. "I'm not a walk-in-the-park southpaw." "

Julian

2004-03-26T20:46:00.000-08:00

Vultures and Crows

There are a lot of crows (or are they ravens?) around this part of Canberra at the moment. I saw some on my way back to my car after work yesterday, near the old "East Block" (now Australian Archives) here in Inner South Canberra. And now one of these birds has just stopped by my window.

I noticed the heavy feathering around their necks, which made me wonder why scavengers like crows would not have bare necks like vultures. The usual explanation for the vulture's naked neck is that feathers would get too messy when the bird was feeding deeply inside carcases. So why don't crows also have bare necks? Instead they actually have heavily feathered necks.

I suppose the vulture story is true. The only other possibility that occurs to me is that maybe having bare necks would mean that other vultures competing for the same carcase would not be able to peck at their feathers (in the way that caged hens do to each other) - but I don't know if vultures do, in fact, fight over carcases.

[Note added later, 29 July 2004] I just saw a documentary on vultures. It seems clear that most vultures fight over carcases, as expected. So the idea that they have bare heads and necks to avoid having feathers plucked out in fights seems possible.

Julian

2004-03-01T16:53:00.000-08:00

There are three notes below: "The Man Born Blind"; "Plants as Doctors?"; "The Peacock's Tail: the Aftermath of an Arms Race?"

The Man Born Blind

Here is an article I published several years ago, together with some comments on Oliver Sacks' remarks on the same topic:

Seeing is Perceiving

by Julian David O'Dea

New Testament miracles of curing may be given naturalistic explanations. It may be argued that conditions were "hysterical" (all in the mind) and therefore subject to cure by suggestion. However, some New Testament cures are harder to explain along these lines [1].

Another possibility is that ordinary physical explanations can be proposed. For example, Tobias' cure of his father's blindness in the Book of Tobit could have been due to the use of a material with appropriate chemical properties to clear the cornea of the eye. Lemon juice has been used as a folk remedy for so-called "cataract", as the writer James Thurber mentioned in his correspondence [2]. Thurber had a lot of eye problems himself and was naturally interested in such matters.

If one takes the account purely at face value, Jesus' cure of "The man born blind" is not in either of the above categories. It was not "all in the mind", nor are the extraordinary and, as far as I am aware, previously unremarked perceptual aspects explicable in natural terms.

John 9, "As he passed by, he saw a man blind from his birth...We know that this is our son, and that he was born blind...Never since the world began has it been heard that any one opened the eyes of a man born blind."

This was not a case of "hysterical blindness" because the man was blind from birth. This point is made throughout the Gospel passage and his parents affirm it. It is possible that Jesus used some obscure physical cure (he "made clay of the spittle and anointed the man's eyes with the clay") to restore his sight. What remains extraordinary is the perceptual ability of the man immediately after his vision was restored.

In a classic study [3], Gregory and Wallace provided a detailed description of the aftermath of a vision-restoring operation on a man who had been effectively blind almost from birth and who, at the age of 52, recovered vision as a result of corneal grafting operations. This man had a lot of trouble using his new vision. He found that although he had vision he had little useful perception. This classic, rather sad case underscored what had been noted for some time, namely what Zangwill in his Foreword to Gregory and Wallace's book had called " the slow, laborious and imperfect way in which the perception of form is acquired by these patients [who recover their vision after early and long-standing blindness] and their liability to emotional 'crises' as they come to discover the true extent of their disability as sighted persons."

In marked contrast, there is no suggestion in the Gospel account that the man had any trouble perceiving his environment as soon as he received vision. In the case described by Gregory and Wallace the man after his operation "...did not find faces 'easy' objects. He did not look at a speaker's face, and made nothing of facial expressions." However the man in the New Testament had no problems in his dealings with the Pharisees and seemed very satisfied with his situation. There is no suggestion in the Gospel account that "The man born blind" had any trouble perceiving his environment as soon as he received vision.

Another case, more recent than the one described by Gregory and Wallace, was that of Judy Taylor, an English woman who recovered her vision as an adult thanks to a cataract operation. She had gradually lost her sight until she became blind at nine years of age. She wrote a book [4] in which she describes her experiences before and after the operation. Even though she had had vision in her childhood she still had trouble learning to see properly after her operation. She had trouble with colours and perspective and objects had to be identified by the familiar means of touch before they could be recognised visually.

So there is more to the New Testament case than meets the eye. One could argue that the man's ability to use his sight effectively as soon as he gained it was the greater miracle. The man would have had to receive not only an optical cure but also a mind trained to perceive [5].

Mark 8: 22-26: "And they came to Bethsaida. And some people brought him a blind man, and begged him to touch him. And they took the blind man by the hand, and led him out of the village; and when he had spit on his eyes and laid his hands upon him, he asked him, 'Do you see anything?' And he looked up and said, 'I see men; but they look like trees, walking.' Then again he laid his hands upon his eyes; and he looked intently and was restored, and saw everything clearly."

This case is a lot less clear cut. There is no indication of whether the man was blind from birth or early in his life, or had become blind later in life. Nonetheless the "two stage" nature of the cure is intriguing. What did the man mean when he made the puzzling remark that he saw "...men, but they look like trees, walking"? Was he trying to say that his perception was abnormal, that people looked like trees - that is did not "make sense" visually? In other words, did he mean that they looked like nondescript vertical objects? Or was it simply that they were blurred or unclear? In any case Jesus made a second follow-up attempt at a full cure, "again he laid his hands upon his eyes" and afterwards the man "saw everything clearly".

There is the intriguing possibility that this man was, like Judy Taylor, someone who became blind in early life after having had some experience with vision. Perhaps his initial perceptual problems (seeing "...men, but they look like trees, walking") were like those that Mrs Taylor experienced on regaining her vision. In the Biblical case Jesus may have been able to move on in the second part of the cure to correct the perceptual problem.

In the first miracle discussed there is no question that the cure, as described, would have had to involve a perceptual cure as well as an optical cure. My remarks on the second miracle are much more speculative, but I think worth making.

What does all this mean to a modern reader? I think it could mean a number of things depending on one's personal approach to belief. One thing is clear. The account of the miracle of "The man born blind" is an even more extraordinary story than the writer could have realised, because a writer of the time would have had no way of knowing about the impossibility of normal perception following a purely optical cure. Only modern medicine, with its cures for chronic blindness, has disclosed that.

Acknowledgments

I wish to thank the Revd Peter Mendham and Fr Keating OP for helpful discussions.

References

1. Leavesley, JH (1990) discusses the issue of cures of "hysterical" conditions in his Potions and Panaceas: Physicians and Prophets, Australian Broadcasting Corporation, Crows Nest, New South Wales. He also mentions cases such as the curing of congenital lameness in the New Testament which are particularly impressive because they seem to have been complete cures of genuine, chronic physical disabilities without the lingering problems one would expect and which would require (in modern terms) physiotherapy. Leavesley's book is based on a series of radio talks. There are some fascinating things in the book, including mention of a brilliant and extraordinary medical explanation for Lot's wife being turned into a "pillar of salt".

2. Thurber, H and Weeks, E, eds (1981) Selected Letters of James Thurber, Little, Brown and Company, USA, p.91.

3. Gregory, RL and Wallace, JG (1963) Recovery from Early Blindness: A Case Study, Experimental Psychology Society Monograph No.2, United Kingdom. Professor Richard Gregory is a prominent and effective writer on science. He edited the Oxford Companion to the Mind.

4. Taylor, J (1989) As I See It, Grafton Books, London. A condensed version appeared in Readers Digest of September 1990.

5. Dr John Grigg, an ophthalmologist at the Sydney Eye Hospital, advised me recently that perceptual skills must be developed during the first nine years of life while the brain is still capable of such learning ("plastic"). Functional sight cannot be achieved without this childhood experience.

ARTICLE ENDS

Some time after I published the above in a journal called "St Mark's Review", I came across Oliver Sacks' essay "To See and Not See" in his book "An Anthropologist on Mars". Discussing cases in which sight is restored after long-term blindness, he writes "What would vision be like in such a patient? Would it be 'normal' from the moment vision was restored? That is what one might think at first. That is the commonsensical notion - that the eyes will be opened, the scales will fall from them, and (in the words of the New Testament) the blind man will 'receive' sight. But could it be that simple? Was not experience necessary to see? Did one not have to learn to see?"

Sacks also provides this footnote: "There is a hint of something stranger, more complex, in Mark's description [in the New Testament] of the miracle at Bethsaida, for here, at first, the blind man saw 'men as trees, walking', and only subsequently was his eyesight fully restored (Mark 8: 22-6)."

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Plants as Doctors?

For some time, I have toyed with the idea that plants might provide substances of medical value to animals that perform useful services for them. For example, do fruiting plants provide medically useful chemicals to monkeys that eat their fruit and help spread their seeds? Could plants provide some curative products to animals that eat their foliage? That is, could a plant's leaves or fruit provide chemicals designed to help prevent or cure animals' diseases?

Certainly plants frequently secrete materials that are intended to stop animals from feeding on them; but could they do the opposite and encourage the health and survival of animals that render them services - such as spreading their seeds or fertilising them with their droppings - by providing them with useful medications?

Is it possible that some of the useful drugs that are derived from plants have their origin in keeping wild animals healthy - for the mutual benefit of the plants and animals? Is this one reason why fruit seems to be so valuable in the human diet?

There is one case that appears to show "proof-of-concept". For an account see "New Scientist" (UK) - the issue of 30 May 1998, p.27. The note is short so I'll quote it in full:

" A Beautiful Way to Keep Bees Healthy

This flower [illustrated], which is native to South and Central America, lavishes an unexpected gift on the wild trigona bees that pollinate it - a coat of resin spiked with powerful antibiotics that probably help keep their nests free of harmful bacteria.

John Loquvam of the University of Alaska in Fairbanks exposed bacteria known to infest the hives of honey bees to the resin of the flower, *Clusia grandiflora*. The resin was almost as effective at killing the bacteria as conventional antibiotics. 'It's the first time this has been shown in any plant as a pollinator reward', says Loquvam.

Resin from the female plants was far more potent than extracts from male plants. Loquvam suspects the females are compensating for the fact that males produce 15 times as many flowers. "

It seems likely that this principle - of plants providing useful animals with medicinal rewards - will be found to apply in other cases as well. It would certainly be in the interests of plants to ensure that useful animals remain free from illness and able to continue to serve the plants' purposes.

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The Peacock's Tail: the Aftermath of an Arms Race?

JD O'Dea, Canberra, Australia

Petrie et al. (1991) provided evidence of a correlation between the number of eye-spots (ocelli) a peacock has on his tail and his mating success.

Manning and Hartley (1991) referred to these data and suggested that females are assessing symmetry, which they indicate is related to number of ocelli, rather than "counting ocelli" for example.

I wish to suggest that the data of Petrie et al. (1991) are most readily interpreted along the lines that female birds are stimulated by viewing eye-spots on the male's train, and that once sufficient of this visual stimulus has been continually available the female is ready to mate. Normally, this will be with a male which is effective at providing eye-spots to the female's visual field: that is, a male bird which has an array of ocelli over as large an area of her visual field as possible. A bigger train (with more ocelli) will cover more of her visual field and is more likely to maintain the stimulus of an eye-spot wherever the focus of her visual attention may wander.

Perhaps there is no need to invoke Zahavi-type hypotheses of indications of fitness, which have been advanced at times to explain the evolution of the peacock's huge tail (eg. Diamond, 1990). Simple competition among males to increase the size of the tail to maximise the effect of the eye-spot stimulus by covering as much as possible of the female's angle of vision may be sufficient explanation.

As Ridley (1981) notes, the eye, or an imitation eye, seems to be important as a behavioural releaser in a range of animals. The same author suggests that the train of the peacock serves merely as a vehicle for the ocelli, and that the effect of female preference is achieved through the form of stimulation or "hypnosis" exerted by the most perfect array of "eyes" on the expanded fan. The "eyes", he suggests, are carefully "designed" to have the maximum psychological effect on the peahen. Ridley (1981) refers to the power of the peacock's train lying in its supernormal mimicry of the obsessive fascination of real eyes.

Enquist and Arak (1993) have considered the concept that perceptual bias may play a role in sexual selection with resultant signal exaggeration.

I am suggesting here that the data of Petrie et al. (1991), the possibility of signal exaggeration (Enquist and Arak, 1993), and a variant of the ideas of Ridley (1981) may be getting us closer to a simple hypothesis to explain the evolution of the peacock's tail. This simple hypothesis does not require the peahen to count eye-spots, assess symmetry or be "hypnotised" by appreciation of a complex pattern (cf. Ridley, 1981) but merely to respond to her experience of a single releaser, the eye-spot.

In summary, the present suggestion is that the peahen is stimulated by the supernormal stimulus provided by the presentation of "eyes" in a large part of her visual field giving her a persistent form of stimulation. Male birds with the most coverage of the visual field (the largest trains with the most spots) will be the most sexually successful.

REFERENCES

Diamond, J. 1990. Kung Fu kerosene drinking. Natural History, (7), 20-24.

Enquist, M., and Arak, A. (1993) Selection of exaggerated male traits by female aesthetic senses. Nature 361:446-448.

Manning, J.T. & Hartley, M.A. 1991. Symmetry and ornamentation are correlated in the peacock's train. Anim. Behav., 42, 1020-1021.

Petrie, M., Halliday, T.R. & Sanders, C. 1991. Peahens prefer peacocks with elaborate trains. Anim. Behav., 41, 323-331.

Ridley, M. 1981. How the peacock got his tail. New. Sci., 91, (1266), 398-401.