Well, when I said that the last post would stir up some controversy, I wasn't wrong. In the comments section, someone has already accused me of "political correctness" for refusing to draw the conclusion that the two alleles reported in the study are being selected due to their effects on brain size. This accusation was predictable, and it is wrong.
Political correctness has absolutely nothing to do with the proper interpretation of this study. If I thought that the only explanation for the positive selection was the effect of the mutation on brain size, I would have no problem whatsoever in saying that. At present, however, we simply don't know what the exact effect of the mutation is.
We know that the gene is involved in brain size determination, but that does not mean that the mutation in question has anything at all to do with increasing or decreasing brain size. It doesn't mean that the allele results in better brain function. It doesn't mean that people with this allele are smarter than those without it. When the researchers report that an allele of this gene has been subjected to positive selection, and that the gene therefore continues to evolve adaptively, it means just that and nothing more. Determining why the allele is positively selected requires that we study the effects of the allele.
Here's an example that might help illustrate things: the sickle cell trait. I have not run the statistics, but I'm reasonably confident that the allele for this trait shows the effects of positive selection in some populations. Yet the allele does not have a postive effect on the normal functioning of the gene. In fact, the effect of this allele is extremely negative in homozygotes. The positive selection stems from the effect that this trait has in increasing resistance to a disease, not in its effects on the oxygen-carrying functions of hemoglobin.
For all we know, the situation with either or both of the alleles discussed in these two studies is exactly the same - they might actually have a negative impact on brain size, but be positively selected for other reasons. It is also possible that the reason that these alleles have been positively selected is because they result in an enormous increase in intelligence. But we don't know that, either.
Restricting the conclusions that you draw from a study to those supported by what the study actually demonstrates is not political correctness. It's just responsible science.
3 comments:
Perfect conclusion.
"Restricting the conclusions that you draw from a study to those supported by what the study actually demonstrates is not political correctness. It's just responsible science."
That's an awfully noble soundin' conclusion you've got there, but it's also misleading and a silly caricature of science. Real scientists (or science-minded folk) don’t just talk about data like it’s some inert, self-evident object lying on the table but actually actively interpret data - all the data together - make predictions and inferences from it, and follow-up on those inferences, which may or may not prove correct. You say: “They shouldn't get excited because these results actually don't say anything about intelligence." But that isn’t exactly true. If the data didn’t “say anything about intelligence”, no scientist would ever purposely test, using the best methods available (i.e. IQ), to see if these genes are related to brain-size/intelligence, but what is obvious, to any rational person, is that these are going to be among the first things that the scientists will test.
My question to you is why is this so? Why are scientists going to immediately give people with this gene an IQ test instead of measure their shoe size, or how well they play tennis, or what color their eyes are? The answer is that no matter what the scientists measure about people with this gene they aren’t choosing what to measure at random, they are making informed choices about what to measure, based on logic and evidence about what is most likely to get results – and that in doing this they are contradicting your description of “responsible science”. What political correctness is, is using this caricature of science only to conveniently shut up certa in predictions and inferences. Political correctness is calling names and spitting venom at those who make such inferences when you find them politically or personally unappealing, such as race differences in intelligence (which I suspect you know lit tle of the scientific evidence either for against).
One thing that is certain is that Bruce Lahn himself is not a responsible scientist by your rather dubious criteria:
”Commenting on these critics' suggestions that the alleles could have spread for some reason other than their effects on the brain, Dr. Lahn said he thought such objections were in part scientifically based and in part due to reluctance to acknowledge that selection could occur in a trait as controversial as brain function.
The microcephalin and ASPM genes are known to be involved in determining brain size and so far have no other known function, he said. They are known to have been under selective pressure during primate evolution as brain size increased, and the chances seem "pretty good" that the new alleles are a continuation of that process, Dr. Lahn said.”
And from the Washington Post:
”For the microcephalin gene, the variation arose about 37,000 years ago, about the time period when art, music and tool-making were emerging, Lahn said. For ASPM, the variation arose about 5,800 years ago, roughly correlating with the development of written language, spread of agriculture and development of cities, he said.”
Note that Lahn has been “irresponsible”, by your definition, by voicing personal likely interpretations on what the data could mean. Note that anybody that’s read Darwin and knows there is an important relationship between brain-size and intelligence (EQ) across evolution, and for human evolu tion in particular. I recommend his Chapter 11 in , where he updates his classic book and also comments that what applies between species, also applies within for humans, as well as affirms that there are race differences in brain size. Chapter 12 reviews the evidence for the real association between brain size and IQ in humans..
Sorry the last paragraph should have been this:
“Note that Lahn has been “irresponsible”, by your definition, by voicing personal likely interpretations on what the data could mean. Note that anybody that’s read Darwin and Harry Jerison knows there is an important relationship between brain-size and intelligence (EQ) across evolution, and for human evolution in particular. I recommend his Chapter 11 in The Handbook of Intelligence, where he updates his classic book and also comments that what applies between species, also applies within for humans, as well as affirms that there are race differences in brain size. Chapter 12 reviews the evidence for the real association between brain size and IQ in humans.”
Including links to Harry Jerison’s Evolution of the Brain and Intelligence (under his name) and to the The Handbook of Intelligence under the title of the book.
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