The controversial scientist discusses the ongoing evolution of humans.

lahn.jpg 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.

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.

Ernst Mayr said there is no way a new human species could originate, that there are no isolated human pockets where human speciation could generate. But, Jonas Salk said a new domain of evolution was created with the advent of the human mind and culture, what he called “sociometabiological evolution.” In this realm, mind and culture can drive biological evolution and could generate a new species.
I think Salk’s scenario is reasonable. My sense is humans are almost certainly going to speciate, that we are going to become a very different species, one that appears and behaves very differently from humans today. I have no doubt, not even a trace of doubt that this is going to happen. This is not even a hypothesis. Speciation is a process that is so inherent to the life phenomenon that it really has to continue. Now, how this will occur I don’t know. It could be one gene.

Just one gene?
In the wild, people have found that one gene has contributed to speciation. The species who have that gene and the ones who don’t cannot breed with each other.

There doesn’t even have to be biological incompatibility. There are a lot of species that could breed in zoos, but in the wild they are not willing to breed; therefore they are different species. If you have that gene, you are just inordinately attracted to people who have that gene and not attracted to people who don’t. It could be due to an olfactory response or it could be cognitive.

I have to ask: Being immersed in genetics and the whole Darwinian perspective, does it make you a ruthless S.O.B.?
I ask that question to myself all the time. It’s a very profound, important question. At the end of the day, it’s competition for survival, for resources. And if a brutal human phenomenon such as genocide can be explained in the context of that, so be it. That’s how it is.

Does that make me no longer sensitive to all these important values, the values of equality and compassion? I think it doesn’t. The brain has an emotional center and it has a rational center. Pursuing science, at least the execution part, has to do with the rational center, but what I do, which includes pursuing science, and what I like and don’t like, comes from the emotional center. We don’t know how that works, but it doesn’t mean that it ceases to have an important function.

Originally published September 11, 2006


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