Reply #10: Just by the by, I came upon an interesting article on lice and human

[Garbo 2004]

evolution the other day. (Apropos of already extant species mutating and evolving.)

Oct. 4, 2004 – A University of Utah study showing how lice evolved with the people they infested reveals that a now-extinct species of early human came into direct contact with our species about 25,000 years ago and spread the parasites to our ancestors...

...The new study confirmed several events in primate and human evolution. The researchers found chimp lice and human lice diverged roughly 5.6 million years ago, consistent with previous evidence that chimps and human ancestors diverged from a common ancestor about 5.5 million years ago.

The study also supports the controversial view that there was a “bottleneck” or reduction in the global Homo sapiens population to only about 10,000 people about 100,000 to 50,000 years ago. Rogers and others have proposed the bottleneck may have occurred because of a mass die-off of early humans due to a globally catastrophic volcanic eruption. Others believe the population bottleneck seen in human genes happened because only a small group of human ancestors left Africa in the second wave 150,000 to 50,000 years ago, then reproduced to cause a sudden population expansion.

The new study used the mutation rate in lice and comparisons of genetic differences among lice to find a similar population bottleneck in the group of head lice that infested early Homo sapiens, but no such bottleneck in the population of the lice on the archaic human species. That means archaic humans didn’t go through the same population shrinkage and thus must have spread their lice to Homo sapiens sometime after 50,000 years ago. Rogers speculates contact occurred 25,000 or 30,000 years ago. http://www.utah.edu/unews/releases/04/oct/licemen.html

Some scientists question that homo sapiens and homo erectus interacted as suggested by the study's authors, but the divergence of lice in chimps and humans in interesting in itself.

A BBC article: http://news.bbc.co.uk/1/hi/sci/tech/3715132.stm

Another article: http://dsc.discovery.com/news/briefs/20041004/lice.htm