Lice Evolution May Reflect sapiens/erectus Contact

From: Rich Travsky (traRvEsky_at_hotmMOVEail.com)
Date: 10/05/04 

Date: Tue, 05 Oct 2004 13:11:41 -0600

Lengthy but worth it...

 http://www.utah.edu/unews/releases/04/oct/licemen.html

 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 study found modern humans have two genetically distinct types
 of head lice. One type is found worldwide and evolved on the
 ancestors of our species, Homo sapiens. The second type is found
 only in the Americas, evolved on another early human species
 (possibly Homo erectus) and jumped to Homo sapiens during fights,
 sex, sharing of clothes or perhaps cannibalism.

 “We’ve discovered the ‘smoking louse’ that reveals direct contact
 between two early species of humans,” probably in Asia about 25,000
 to 30,000 years ago, says study leader Dale Clayton, a professor of
 biology at the University of Utah. “Kids today have head lice that
 evolved on two species of cavemen. One species led to us. The other
 species went extinct.”

 Alan Rogers, a co-author of the study and professor of anthropology
 at the University of Utah, says: “The record of our past is written
 in our parasites.”

 The analysis of lice genes also confirmed two other key developments
 in human evolution. First, it verified studies showing how and when
 various species branched off the family tree of primates and humans.
 Second, it confirmed the “out of Africa” theory that the population
 of Homo sapiens mushroomed after a small band of the early humans
 left Africa sometime between 150,000 and 50,000 years ago.

 The study will be published online Oct. 5 in the Public Library of
 Science journal PLoS Biology. ...
 ...
 Transmission of the second type of lice from a now-extinct human
 species to Homo sapiens may have happened during mating, so Reed
 plans a study of pubic or crab lice – which only spread sexually –
 to confirm or disprove that possibility. Clayton and Rogers say it’s
 also possible our ancestors got the second kind of head lice by
 fighting with or cannibalizing another human species – or by sharing
 or stealing their clothing.

 Clayton says evidence of contact between two species of humans is
 surprising because “Homo erectus has long been thought to have gone
 extinct hundreds of thousands of years ago,” although recent studies
 suggested Homo sapiens might have had contact with Homo erectus in
 Asia 50,000 years ago.

 Reed says: “Not only did modern humans live contemporaneously with
 close cousins such as Neanderthals, but also with more archaic
 hominids such as Homo erectus, a species that we have not shared a
 common ancestor with for over a million years. It is amazing to know
 that we had physical contact with another species of human. We either
 battled with them, or lived with them or even mated with them.
 Regardless, we touched them, and that is pretty dramatic to think
 about.”

 Reed wonders if contact with our species proved fatal.

 “When scientists first determined that we (Homo sapiens) were
 contemporaneous with Neanderthals (Homo neanderthalensis) in Europe,
 it was suspicious that our contact with them immediately preceded their
 extinction,” Reed says. “Our study has provided evidence that we had
 contact with Homo erectus in Asia just prior to the extinction of that
 species as well. Did we cause the extinction of two other species of
 humans?”
 ...
 The researchers analyzed the physical appearance and genetic material
 (mitochondrial DNA) of modern human head lice, Pediculus humanus, to
 construct a family tree for lice showing when various species branched
 off from each other. Genes of modern lice also were used to reconstruct
 their population histories over time.

 The researchers found the family tree of the lice closely mirrors the
 previously published family tree of humans and their primate ancestors.
 ...
 Scientists already knew that early ancestors of our species, Homo
 sapiens, diverged from other archaic humans about 1.2 million years ago.
 (There is semantic debate over whether those archaic humans should be
 called Homo erectus, or whether the name should be reserved for their
 more recent descendants.) The new study showed two almost
 identical-looking but genetically different strains of head lice
 diverged 1.18 million years ago. That indicates each of the two kinds
 of head lice infested a different species of early human as the human
 species diverged.

 Genes from both types of head lice are found on people today, suggesting
 that after infesting Homo erectus or another archaic human species for 1
 million years, the second louse type jumped from that soon-to-be-extinct
 species and onto Homo sapiens.

 “In order for the archaic human lice to still exist on modern humans,
 archaic and modern humans had to coexist in time and space,” Clayton
 says.

 Some of the findings conflict with two major theories of human evolution
 – the “replacement model” and “multiregional model” and instead fit best
 with a third theory known as the “diffusion wave model.”
 ...
 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.
 ...

This particular article didn't make it quite clear why it was erectus and
not neanderthal, given the dates involved. A New Scientist article
clarifies a bit:

 http://www.newscientist.com/news/news.jsp?id=ns99996489
 ...
 Reed and colleagues found that the two louse lineages were very different,
 making it extremely unlikely that they evolved to their current state on
 the same species. It is probable, he says, that the louse found only in
 the Americas evolved on H. erectus while the worldwide louse evolved on
 the line that eventually became H. sapiens.

 Relatively recently - approximately 100,000 years ago - the New World louse
 found its way back onto H. sapiens in Asia who then carried it with them to
 the Americas. The researchers say there must have been some contact between
 the two hominid species before H. erectus finally died out.

 But there are alternative explanations for the findings. Mark Stoneking, an
 expert on human evolution from the Max Planck Institute for Evolutionary
 Anthropology in Leipzig, Germany, says the findings depend on the last
 common ancestor of the two species of lice having lived almost 1.2 million
 years ago. The calculation to obtain this figure depends on the size of the
 lice population at that time. So if the population estimates are inaccurate,
 the results may be misleading, he says.
 ...

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