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Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: daniel buchanan on 12/05/2009 10:30:02

Title: How were different human races formed?
Post by: daniel buchanan on 12/05/2009 10:30:02

daniel buchanan  asked the Naked Scientists:
   
Hi guys..

How were difference human races formed?

Dan, from London

What do you think?

Title: How were different human races formed?
Post by: chris on 13/05/2009 10:07:09

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

Title: How were different human races formed?
Post by: thedoc on 10/06/2009 10:16:13

Listen to the answer to this question on our podcast. (http://www.thenakedscientists.com/HTML/podcasts/show/2009.05.24/)