Bruce Lahn Courtesy of the University of Chicago
Geneticist Bruce Lahn first made a name for himself when he paired with David Page, director of MIT's Whitehead Institute for Biomedical Research, to craft a novel theory on the origins of the Y chromosome. But Lahn is perhaps best known for his paper on the evolution of the human brain, and the implications for intelligence and race that have become attached to it.
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Lahn's paper on the recent evolution of the human brain asserts that new versions of two genes are currently spreading through the human population, and that these genes are more prevalent in some geographic regions than others. He has speculated that these genes may be linked to brain size and intelligence and has wondered if the mutations—one of which took place roughly 40,000 years ago, the other, 5,800 years ago—correlate with the development of art, written language, and the founding of cities. And he stepped on more than a few feet when he noted that, geographically speaking, the changes had occurred pretty much everywhere but sub-Saharan Africa.
Some scientists have criticized Lahn's work as inconclusive, challenging his claims that these genes are integral to brain evolution. His critics brand Lahn's speculation as irresponsible, especially given the volatile combination of genetics, intelligence, and race that his ideas encompass.
Lahn's defenders say he was merely practicing good science, had no agenda, and that the controversy surrounding his work was merely his underestimating the political reaction to his research.
Can you give us some background on your work and your finding that the human brain is still evolving?
We started out looking at genes that might be important for human brain evolution by comparing specific genes in the human genome with sequences in other species, particularly other primates. The goal was to understand genes whose changes have been important in the emergence of the human phenotype, especially the enlargement of the human brain and all the great things that came along with that. We published a paper showing that genes important for brain development seem to have evolved more rapidly in the evolutionary lineage leading to humans when compared to nonhuman primate lineages, or nonprimate mammal lineages.
So the mutation process continues.
What happens is a random chance mutation that is advantageous strikes only one individual in a population belonging to a particular species. The individual with that mutation will reproduce a little better. Some of their offspring would inherit this mutation and also reproduce a little better because the mutation makes them more attractive, stronger, whatever. Over time this mutation would spread in the population to the point where it basically takes over the entire population and everybody has it. One sweep fixing one advantageous mutation. Another sweep comes along and fixes another. So we asked, given that the observed differences between humans and other species are likely due to the repeated occurrence of these sweeps, is it possible that we could observe one of these sweeps in action now?
We examined the variation of two of these genes and found that there indeed has been an advantageous variant in each of these two genes that arose very recently. One appeared roughly 6,000 years ago and is now found in over 30 percent of all the chromosomes in the world. The other mutated about 40,000 years ago and is now in over 70 percent of the chromosomes out there. It's almost like the cell phone. The first person has it and everybody wants it.