Well, there is even more proof that we are a very young species. Today I viewed an impressive documentary on the National Geographic Channel describing work by Spencer Wells on the relatedness of all men. He used DNA sequences from the human Y chromosome. This chromosome was chosen because it doesn’t have a mate. Men are XY and there are no common sequences between them. Other chromosomes including the X in women have a mate or sister chromatid with which recombination can happen during the development of eggs or sperm. Recombination or exchanges between of parts of one chromosome with its mate scrambles the genetic pattern after a few generations. Since the Y has no mate it can’t undergo recombination so it’s sequence does not change except for mutation. Wells follows the rare mutations on the human Y chromosome to get a pattern of relatedness. This analysis shows all human Y chromosomes trace back to a single line that existed about 50,000 years ago. The number of mutations detected act as a somewhat imperfect clock. Mitochondrial DNA which is only inherited through women provides a similar means of analysis that traces the female line. Mitochondrial DNA has previously been used to trace our lineage back to a single women or small group of individuals. Thus both independent types of analysis come up with approximately the same answer although the mitochondrial eve seems to be somewhat older than the Y man. Both analyses say the we are a very young species that took over the world in a relatively short period of time. The author notes that the usual depictions of Adam as a light skinned European is incorrect. He was African.
I highly recommend this program. Information can be found at the link below.
http://www.nationalgeographic.com/adventure/0508/excerpt1.html?fs=www5.nationalgeographic.com
2 comments:
Recently Spencer Wells appeared on the Today Show and traced the genetic origins of the hosts.
See http://msnbc.msn.com/id/10095659/
The results showed that Matt Lauer's paternal ancestors migrated from the Middle East and Mediterranean region, as might be expected from his paternal Jewish ancestors. However, Katie Couric's genetic map showed migration from the northern parts of Europe even though her mother is Jewish and the test was based upon mitochondrial DNA. Does this demonstrate that this kind of testing is inherently unreliable?
This demonstrates that the different ethnics groups contain mixtures of genetic markers. Wells's test can only show statistical likelihoods but cannot prove ethnic origins with infallibility. You can see statistical trends only with large numbers of samples, but you cannot look at any one person and say for 100% certainty what their genetic identity is, in terms of ethnicity.
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