The Frontal Cortex

Genes, Diversity, Brains

We spend so much time fixating on our genetic differences that we tend to overlook the places where the human genome has converged over time.

In a study published yesterday in Nature Genetics, geneticists from France’s Pasteur Institute compared DNA variations in people from Japan, China, Nigeria and northwest Europe. They found 582 genes associated with skin color, hair texture and other physiological characteristics. These are likely just a fraction of the genes historically tweaked by regional variations in selective pressures, producing the differences between — for example — an Australian Aborigine and a Labrador Inuit.

What do the Nature Genetics findings say about human diversity? When it comes to certain physical characteristics, such as hair and eye color, the groups studied followed diverging evolutionary trajectories. But the researchers found that most genetic predispositions to disease actually converged over time. In some ways, our ancestors became more different; in other ways, they became more similar.

The researchers didn’t find any group-based difference of of genes involving neuronal development, and cautioned against automatically assuming that different groups of people evolved different degrees of intelligence.

“There is not evidence at all of any population differences in genes associated with neurological development or cognitive performance,” wrote study author Lluis Quintana-Murci in an email. “In addition, I even wonder if there are genes really associated with ‘cognitive performance.'”

Allow me to play the devil’s advocate: wouldn’t neural diversity be a good thing? I can understand why negative selection would lead to a convergence of “globally reduced population differentiation at amino acid-altering mutations” in disease-related genes, but it’s not as if there is only one solution to the problem of thinking. Different environments/cultures/societies/etc. seem to emphasize slightly different modes of thought. I guess I’m surprised that the brain seems, at least according to this tentative study, less genetically tailored to its environment than the texture of our hair.

To which the devil’s advocate of my devil’s advocate replies: but that’s why we have neural plasticity! You don’t need to change genes within the brain in order to produce a brain that fits the locale. The brain changes itself.

Comments

  1. #1 Steve Silberman
    February 8, 2008

    Fascinating, Jonah. And that last point is brilliant.

  2. #2 Crusty Dem
    February 8, 2008

    There are certainly genes associated with cognitive performance. If you have a mutation in MeCP2, your performance will suffer greatly (although if you’re a male, you’ll be dead). Ok, that’s a bit extreme, but given the number of genetic mutations found in so many serious, and not so serious, disorders, it’s absolutely impossible that there are no genes associated with cognitive performance. Whether there are population-based differences in the distribution of these genes (and even if there is, that wouldn’t necessarily mean population-based cognitive differences, since no attempts to determine the genes involved could be comprehensive…) is a completely distinct question that there is no need to measure, in my opinion.

  3. #3 Derek James
    February 8, 2008

    “In addition, I even wonder if there are genes really associated with ‘cognitive performance.'”

    I agree with Crusty Dem. This seems like a pretty silly thing to say.

    Also, are you going to blog about latest article in Seed, on the Blue Brain project? I haven’t read it yet, but it looks interesting.

  4. #4 Marc
    February 8, 2008

    Even with the benefit of neural plasticity, it still seems to me there would have to be selection for different thinking styles based on environmental differences. Maybe I’m off base here, but I feel sometimes there is a pressure to avoid making this postulation because it could so easily be twisted into a politically incorrect stance. The statement about no genes being associated with cognitive performance seems like just that: an effort to avoid this study being misconstrued in a politically incorrect way. It’s hard to imagine a geneticist making that statement otherwise.

  5. #5 Josh
    February 10, 2008

    “In addition, I even wonder if there are genes really associated with ‘cognitive performance.'”

    Hmmm. Like the gene(s) involved in Williams Syndrome?

    Jonah: Since Quintana-Murci has presumably heard of genetic cognitive impairments, do you have any idea what this quote was supposed to mean?

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