ScienceDaily (Oct. 5, 2004) — 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.”
3) The diffusion wave model falls between the other two theories. Like the replacement theory, it says modern humans arose in Africa and spread across the world, Rogers says. Like the multiregional theory, it says those early humans mated with humans elsewhere. THE DIFFUSION WAVE THEORY ADDS A NEW TWIST, NAMELY, THAT THE GENES OF HUMANS SPREADING FROM AFRICA CAME TO DOMINATE THE MODERN HUMAN GENETIC BLUEPRINT BECAUSE WHEN THEY MATED WITH ARCHAIC HUMANS, THE CHILDREN WERE LESS FIT.
“As they come out of Africa, they replace other populations while interbreeding with them,” Clayton says.
The findings in lice are most consistent with the diffusion wave hypothesis, which allows some interbreeding among various forms of early humans but also says the genes of early humans who left Africa came to dominate Homo sapiens, he adds.
Lice Genes Confirm Key Events in Human Evolution
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.
The findings provide independent confirmation of the second “out of Africa” event because genetic analysis shows the population of lice – like their Homo sapiens hosts – also dramatically expanded after the bottleneck." See Link for entire article
If the ancient human parasites are found 'only' in the Americas why are we still fixated on a single East African exit?
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