The genetic history of Africans

This week’s Science magazine has an absorbing article by Sarah Tishkoff et al. on the genetic relationship and evolutionary history of African populations.  (Ann Gibbons has a one-page summary here.)  This project was a massive one, involving DNA genotyping of 1,327 genes in 2,432 Africans from 113 populations, as well as 98 African-Americans and 21 Yemenites. (That’s over 3,385,000 genetic determinations; no wonder the paper has 25 authors!)  There are many results, but I’ll just list the main ones here:

1.  All the hunter-gatherer populations of Africa descend from one ancestral population that is a bit more than 35,000 years old.  This means that African tribes and ethnic groups are very young relative to when African ancestors left the continent to populate the world with modern humans (about 60,000-100,000 years ago).

2.  The population ancestral to the modern African groups appears to have lived in southwest Africa.  Tishkoff et al.  even calculate a migration epicenter:  12.5 degrees E and 17.5 degrees S, near the border of Namibia and Angola.

3.  The genetic profile of Africans put them roughly into groups corresponding to the major language differences (see figure below).  This is not surprising; it shows that almost all intermarriage has occurred within groups that speak the same language.

4.  African-Americans have a complex mixture of genes from many areas, including about 67% Bantu and non-Bantu genes from people who speak Niger-Kordofanian languages (e.g. ,Zulu and Swahili),  8% from other African areas, and 13% from Caucasians.  The authors note that this will make it hard for some African-Americans to trace their roots.

5.  The “out of Africa” group whose migration gave rise to modern humans worldwide has its closest relatives in the group of “blue” populations at the top of the figure below.  These are “Saharan” populations from East Africa. That, then, is where the rest of us came from.

language-groups

The phylogeny of African groups: a massive achievement (Figure from Tishkoff et al.)

5 Comments

  1. newenglandbob
    Posted May 3, 2009 at 12:30 pm | Permalink

    I am a bit confused.

    The “out of Africa” group whose migration gave rise to modern humans worldwide has its closest relatives in the group of “blue” populations at the top of the figure below. These are “Saharan” populations from East Africa. That, then, is where the rest of us came from.

    Most of the world came from these Saharan populations, but the rest of the African populations came from southwest Africa?

    Why would the Saharans get everywhere except most of Africa? Why wouldn’t the Southwest Africans have been able to migrate out?

    • Hempenstein
      Posted May 3, 2009 at 4:39 pm | Permalink

      Haven’t read the piece yet, but somehow I suspect that the ability to navigate the Nile is part of the story.

    • Yair
      Posted May 4, 2009 at 12:46 am | Permalink

      I don’t understand this either. What is the relationship here? If we take the “out of Africa” group, some 60,000 years ago, is this group also the ancestral group of the “blue” populations? How are we descendant from the blue populations if the latest common ancestor of African populations is only 35,000 years old, and ours is 60,000 years old?

      As best I can tell, the “out of Africa” population lived in Africa some 60,000-100,000 years ago, and sent an offshoot into Europe while continuing to evolve in Africa. The African “blue” lineages are those that diverged from its African residents soonest. But that doesn’t seem to be what Coyne is saying, so I’m confused.

  2. Robert Byers
    Posted May 4, 2009 at 3:50 am | Permalink

    Biblical creationist here.
    We don’t come from Africa.
    We come from exactly where the greatest number of languages converge in the old days. That is exactly where the tower of babel is.
    The bible indicates several families moved to Africa including different language groups.
    this genetic stuff misses the point that upon entering africa the peoples had profound physical changes to the the problem of sun and heat/humidity.
    The quick adaptation to Africa demanded quick dna change. This explains dna diversity there.
    These long ages therefore are just misunderstandings of quick dna change needs.
    It is as it looks and as the bible makes boundaries.

    • newenglandbob
      Posted May 4, 2009 at 5:42 am | Permalink

      Sorry, Robert Byers, but the tower of babel and the bible are works of fiction and fantasy and you add more fiction. Many of the bible stories were stolen from other cultures. Your ‘entering Africa’ stuff contradicts the evidence of DNA and fossils, etc. Not even a good try.


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