Tuesday, June 30, 2009

Family Feud

The authors of science zines must spend much time reading one another, because they often carry similar stories even when nothing special in the news has prompted it. If one zine carries an article on, say, border clashes between tribes of chimps in Angola, simply because the subject interests one of the writers, other zines are sure to follow in the next few days with similar articles.

This must explain a recent spate of articles in science zines about how closely all humans are related. None of the zines cite any significant new paper in any major journal. Nevertheless, the point is an interesting one though it is nothing new. It long has been the consensus that it is mathematically necessary, due to the doubling of direct ancestors with each generation, for every person now living to be descended from every person in the world who was alive no further in the past than 7000 years ago who left a still intact line. This is so even if very conservative assumptions about human movements are applied. The number is closer to 5000 years if more liberal and more likely assumptions about migration are used. Even a tiny rate of infiltration by travelers over the steppes, the deserts, and the seas ensures this universal relativity - and migration was often anything but tiny. Also, all living people, no matter how remote, share at least one direct common ancestor by 3000 years ago (more likely 2000).

There is something neat about this. A person may not think of himself as hailing from the banks of the Chang Jiang River or the grasslands of West Africa if his great great grandparents sailed to the US from Ireland in 1849, but it seems that he does. His ancestors hauled stones to Giza too. They quite likely besieged (and defended) Troy. It is worth an occasional thought, while claiming this rather than that heritage, that those other folks are cousins too. Cousins, of course, don't always get along, but it is still worth a thought.

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