Exploring genes

David Dobbs has written a great National Geographic piece on the human compulsion to explore. At the centre of the article is the question of genetic influence.

First, on whether migration has a genetic basis:

[T]here is a mutation that pops up frequently in such discussions: a variant of a gene called DRD4, which helps control dopamine, a chemical brain messenger important in learning and reward. Researchers have repeatedly tied the variant, known as DRD4-7R and carried by roughly 20 percent of all humans, to curiosity and restlessness. …

Most provocatively, several studies tie 7R to human migration. The first large genetic study to do so, led by Chuansheng Chen of the University of California, Irvine in 1999, found 7R more common in present-day migratory cultures than in settled ones. …

Another recent study backs this up. Among Ariaal tribesmen in Africa, those who carry 7R tend to be stronger and better fed than their non-7R peers if they live in nomadic tribes, possibly reflecting better fitness for a nomadic life and perhaps higher status as well. However, 7R carriers tend to be less well nourished if they live as settled villagers. The variant’s value, then, like that of many genes and traits, may depend on the surroundings. A restless person may thrive in a changeable environment but wither in a stable one; likewise with any genes that help produce the restlessness. …

I’m not sold on the DRD4-7R variant story yet, but I am open to the idea that there is a basket of traits that differ between migrants and those who stay. If that is the case, the interesting question is what effect those traits have in other spheres. For example, Galor and Michalopoulos note the DRD4-7R variant in their argument that selection for entrepreneurial traits plays a role in the economic development process. Are migrants naturally more entrepreneurial?

Of course, those who migrate may be different from those they leave simply through chance:

[A] migratory wave can concentrate not just particular types of people on its frothy front edge; it can also concentrate and aid the expansion of any genes that may encourage those people to migrate.

Sometimes a gene rides such a wave passively, more or less by accident—the gene just happens to be common in the leading migrators, so it becomes common in the communities they establish. …

But a migratory wave can also allow genes friendly to migration to drive their own selection. …

Laurent Excoffier, a population geneticist at the University of Bern, thinks something similar occurred with the Quebec loggers. In a 2011 paper Excoffier and some colleagues analyzed centuries of Quebec parish birth, marriage, settlement, and death records and found that the pioneer families behaved and bred in a way that spread both their genes and the traits that drove them to the front. These wave-front couples married and mated sooner than did couples back home, perhaps because they were more impatient folks to begin with and because the frontier gave them access to land and a social atmosphere favorable to starting sooner. This alone produced more children than the “core” families who stayed behind did (9.1 per family versus 7.9, or 15 percent more). … In this case it rapidly raised the share of these families’ genes and cultures within their own population—and thus within North America’s larger population.

Excoffier believes that if this “gene surfing,” as some call it, happened often as humans scattered around the globe, it would have selected for multiple genes that favor curiosity, restlessness, innovation, and risk taking. This could, he says, “help explain some of our exploratory behavior.”

Migration provides an opportunity for strong selection through the new environment that the migrants are exposed to, possibly favouring traits that were neutral or deleterious in the earlier environment. Even if migrants are no different from those they leave, it may not stay the case for long.

As an end note, Razib rightfully asks whether heritability is a better place to focus in exploring this genetic link than looking for genes such as DRD4-7R. I think this is the case in a lot of fields in the short term, including genoeconomics.

One comment

  1. It is a very nice essay indeed but the migration hypothesis of Chen et al. is a stretch. The frequency of 7R hovers around 20% or so in Europe and sub-Saharan Africa. It is absent in Bushmen in southern Africa and it is also absent in Japan and China. It is apparently present in people of northern Siberia and it has bloomed in the New World with frequencies over 1/2 in North American Indians and up to 80 or 90% in Amazonian Indians.

    The literature on effects of 7R points to many likely related traits: childhood ADHD, risk taking, gambling, more active sex lives, and others. Greg Cochran and I wrote a commentary in PNAS a decade ago suggesting that the association was with male violence and warfare rather than with migration. We discussed ways to test our competing hypotheses with Chen and his colleagues but the project never got off the ground.

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