Science Questions

How did human races form?

Sun, 24th May 2009

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Dan, London asked:

How did human races form?


Nina - Well, itís a big question and one can argue that there are no such things as human races, because human races are basically defined by us socially. When you go to Britain or the United States or Brazil or India there would be different groups that would be defined as different races. In many respects races donít exist. What we do see are lots of patterns or genetic variation. Some of these patterns are related to our appearance but those are just a tiny fraction of our genes that actually contribute to these differences in appearance. We have tremendous amounts of variation that donít coincide with these classic racial groups that have been defined in various places. The long and short of it is races are an outdated, ancient construct that weíd best ignore.


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daniel buchanan asked the Naked Scientists: Hi guys.. How were difference human races formed? Dan, from London What do you think? daniel buchanan , Tue, 12th May 2009

Hello Dan.

Broadly speaking, for modern humans this relates largely to a few hundred thousand years of human migration and population bottlenecks. Genetic analysis tells us that modern humans arose in Africa about 250,000 years ago and migrated northwards out of the continent about 50,000 - 100,000 years ago.

As the early pioneers spread out across the Earth communities were isolated and placed, by the environment, under considerable selective pressures. This would have included food supply, disease, temperature and so on.

In Africa, and other equatorial regions, strong sunlight and high temperatures strongly favoured dark skin (to protect against UV-mediated destruction of the essential vitamin folate) and short curly hair (which keeps the head cooler).

However, outside of Africa, where light intensity is lower and the temperature is cooler, there is less risk of UV-induced folate deficiency. At the same time, dark (melanised) skin can impair vitamin D synthesis, which is essential for calcium uptake and hence skeletal development. For this reason those early people who moved further north lost their basal melanisation (i.e. became white), and also had less use for curly hair.

Since these people lived in geographically isolated communities these traits concentrated within these populations, leading to the emergence of distinct-looking races. Insufficient time has passed, however, to allow the genetic divergence that would be required to create novel species.

Hence humans are a bit like dogs - they come in many different shapes and sizes due to selective breeding, but they are all the same species and hence all cross-fertile.

Chris chris, Wed, 13th May 2009

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