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Friday, March 26, 2004

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


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