How long would it take to walk to the ends of the Earth?

"Who started walking out of Africa? Not everybody walked. Very few people walked, and they walked to the ends of the Earth. The geneticists now have found that the people who migrated had a particular gene, and this gene makes you a risk-taker, a wanderer. Bipolarity is an extreme version of this gene, and the people who migrated, they had this gene."

This is a quote from Indian political economist, Deepak Lal, on the BBC radio show, The Forum, which aired 05/24/09. Lal went on to say that the people who inherited this gene for risk-taking are now ethnic minorities, which explains why they tend to "punch above their weight".

But the people who migrated out of Africa are ancestors of us all. If they had a gene 'for' risk-taking, all of us would have it, not just today's ethnic minorities. And, it can't be argued that for genetic reasons ethnic minorities tend to succeed more often than majority populations because the minorities are or were majorities somewhere at some time.

It's amazing how misguided smart people can be about genetics and population history. Granted Lal is an economist, not a population geneticist or anthropologist-- but he spoke so authoritatively! Darwinian scenarios, of the BS as well as plausible variety, are so easy to put forth with an air of confidence! But, is this all air, or does it actually matter when people get it so wrong? We suggest that it does for a number of reasons because it happens in many contexts, with ramifications, not just on BBC radio programmes.

First, the idea of a gene 'for' risk-taking has been reported, but the original study has been difficult to replicate, in part because it's difficult to define risk-taking, and in part because genes 'for' behavior have been quite elusive. Populations considered to be high risk-takers or violent by some, with a high frequency of the DRD4 mutations originally associated with risk-taking, might be considered to be pacific by others, for example. So, this trait is, like most complex traits, difficult to define and genes 'for' it difficult to confirm. If one thinks about genetic mechanisms, many genes would contribute to such traits, and they would be very culture-specific or their manifestation would be, at least.

Second, genes 'for' bipolarity, again as for all complex traits, have not been confirmed. Mapping genes making major contributions to psychiatric disorders has been very problematic, at best. Some candidates have been found, but even they generally account for only a small fraction of the instances.

Third, ethnic minorities are only such at certain times and places.

Fourth, can we really conclude that ethnic minorities are all feisty? It's funny how people with guns, money, or power can seem so much more adventurous than those who haven't the same assets.

These simple (or is it simplistic?) Darwinian arguments reflect incredibly naive population biology. Basically, nobody 'walked out of Africa' in the alleged sense. People did not have travel posters or travel agents. They might go upstream or 'over there' to find game or plants they liked to eat. If nobody was living there (or only brute Homo erectines), they might decide to kick them out and take over a nice campsite. Nobody ever heard of the ends of the earth! They did not know there were island paradises in the Pacific to go vacation at.

Young adults would pair up and move to better pastures, perhaps to get away from their annoying parents or pests in their little hunter-gatherer bands. They would, however, generally stay in touch--not go too far, because family was everything for social survival (and mates in the next generation). Gradual expansion would be on foot and in a sense by everyone, going over the next hill for open territory. Nobody would know they were going anywhere!

Each generation, village exogamy (kin-based mating rules) would mean that the 'explorers'' children would have to return to their former hearth and home to find mates. There would be large amounts of inter-village gene flow, back and forth, each generation.

It is possible that among those who chose to pop over the hill, those more inclined would have some slightly increased probability of doing that. But in the overall scheme of things, genetic drift and other kinds of chance would have watered down any such signal.

The genetic data clearly show that the farther from Africa people are, the smaller the subset of 'African' genetic variants they carry. This does not mean that they purified African adventure genes, and those in Tierra del Fuego aren't pure adventurers, nor less so than the Bantu marauders who captured each other in wars and sold the victims into slavery (unless there is an adventure gene in the slaves that made them turn themselves in?)

In historic times, and in invasions, hordes of armies or boatloads of pilgrims were forced to travel and settle elsewhere, in large numbers. They were not selected based on Indiana Jones genes.

We'll be a lot better off in evolutionary reconstructions, especially as regards behavior which clearly reflects social biases of the authors, if we temper our view based on a realistic understanding of the demographic chaos that is life!