Friday, December 29, 2006

Challenging the link between the human microcephalin gene, evolution, and cognition.

Michael Balter writes an interesting account in Science Magazine over the controversy over the interpretation of data on the microcephalin gene, a gene that regulates brain size. (Microcephaly is the congenital or developmental disorder in which the circumference of the head is smaller than normal because the brain has not developed properly or has stopped growing. )

"...in two papers in Science last year, Lahn reported that variants of the two genes appear to have been strongly favored by recent natural selection (Science, 9 September 2005, pp. 1717 and 1720). That implies that the variants conferred a survival or reproductive benefit, perhaps a cognitive one. In media interviews, Lahn conceded that there was no real evidence natural selection had acted on cognition or intelligence. But both papers pointed out that the mutations arose when key events in human cultural development occurred: The microcephalin variant was dated to about 37,000 years ago, when the first art and symbolism showed up in Europe, and the ASPM variant to 5800 years ago, when the first cities arose.


Lahn's papers also reported the skewed geographic distribution of the genetic variants. Variants in microcephalin turned up in 75% or more of some Europeans and Asians Lahn studied, but in less than 10% of some African groups. The ASPM variant was also much less frequent in Africa. (click on graphic to enlarge).

Bloggers jumped on the news, trumpeting the papers as support for the idea that African Americans have lower intelligence than whites. Two months later, in the conservative National Review Online, columnist John Derbyshire wrote that the research implied that "our cherished national dream of a well-mixed and harmonious meritocracy … may be unattainable."

"Soon after the Science papers were published, Lahn set out to see whether the variants give a cognitive advantage. In one study, Lahn helped controversial psychologist Philippe Rushton of the University of Western Ontario in London, Canada, test whether people who carry the favored variants have higher IQs. Rushton is well known for his claims that African Americans have lower intelligence than whites, and Lahn had found that some genetic variants are common in Europeans and Asians but less frequent among sub-Saharan Africans. But Rushton reported last week at the annual meeting of the International Society for Intelligence Research in San Francisco, California, that he had struck out: The variants conferred no advantage on IQ tests. "[We] had no luck," Rushton told Science, "no matter which way we analyzed the data." Lahn was not a co-author, but his group genotyped the 644 adults of differing ethnicity in the study."

Among some geneticists, there was consternation. "There was no evidence whatsoever that these [genetic variants] have any effect" on differences between people, Altshuler says, adding that the controversy over the work was "easily anticipated." Harvard geneticist Richard Lewontin goes further, criticizing both Lahn and Science for publishing such speculative links to cultural advances. "These two papers are particularly egregious examples of going well beyond the data to try to make a splash," he says. And archaeologist Scott MacEachern of Bowdoin College in Brunswick, Maine, says the archaeological links in the papers are simplistic and outdated. The symbolic revolution, agriculture, and urbanism developed "over many thousands of years, and none was restricted to Europe and the Middle East," he says."

3 comments:

  1. Thanks for your interest in this story!

    best wishes, Michael

    http://www.michaelbalter.com

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  2. Hi Deric,

    I was looking for information about this very topic, and I was amazed to come up with your blog, and find that you have written about this.

    Some pop science writers seemed to have declared that this gene was the vaunted IQ gene, even before evidence proved to the contrary.

    How do you evaluate Lahn's theory that it may have introgressed from an archaic human population. Has anybody serious examined that idea? What is the null hypothesis?

    Some time, I'd like to call you and ask some questions about this.

    Howard Metzenberg

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  3. Howard, the guy you want to talk with is John Hawks, who has an anthropology blog on human evolution (http://johnhawks.net/weblog/). He knows vastly more about this controversy than I do.
    Good to hear from you.
    Deric

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