Saturday, 1 January 2022

Evolution News - Human Head Lice are Making Nits of Creationists

Mummified man of the Ansilta culture found in the Andes of San Juan, Argentina, dating back approximately 2,000 years
Nits on ancient mummies shed light on South American ancestry

The story of the co-evolution of head lice and humans just got a little more interesting, unless you're a Creationist, in which case it just got a lot more difficult to ignore.

Briefly, the human head louse Pediculus humanus capitis diverged from human body louse, Pediculus humanus humanus, at about the same time that humans started wearing clothes. Pediculus humanus (the common ancestor of the two subspecies) was a close relative of the louse found on Chimpanzees, Pediculus schaeffi. In fact the evolution of these louse species and subspecies maps exactly onto our own evolution, both biologically as we diverged from the common ancestor we share with chimpanzees, and as we lost body hair and invented clothes (cultural, rather than biological evolution).

Headlice have accompanied humans throughout their entire existence, so this new method could open the door to a goldmine of information about our ancestors

Dr Alejandra Perotti
Ecology and Evolutionary Biology Section
School of Biological Sciences
University of Reading, Reading, United Kingdom
What is even more interesting is the finding of an international team that the cement head lice use to stick their eggs (or nits) to hair, preserves the DNA in the hair cells. This means we can extract far more DNA from the hair of ancient people who also had head lice, than we can from the fossilised or semi-fossilised teeth and bones that were used until now.

So, using the DNA extracted from the lousy hair of human remains in South America, the Reading team, in association with scientists from Argentina, Wales, Oxford, UK and Denmark, were able to discover:
The high amount of DNA yield from these nit cements really came as a surprise to us and it was striking to me that such small amounts could still give us all this information about who these people were, and how the lice related to other lice species but also giving us hints to possible viral diseases.

There is a hunt out for alternative sources of ancient human DNA and nit cement might be one of those alternatives. I believe that future studies are needed before we really unravel this potential.

Dr Mikkel Winther Pedersen, first author
GLOBE Institute
Faculty of Health and Medical Science
University of Copenhagen, Denmark
  • The sex of each of the human hosts.
  • A genetic link between three of the mummies and humans in Amazonia 2,000 years ago. This shows for the first time that the original population of the San Juan province migrated from the land and rainforests of the Amazon in the North of the continent (south of current Venezuela and Colombia).
  • All ancient human remains studied belong to the founding mitochondrial lineages in South America.
  • The earliest direct evidence of Merkel cell Polymavirus was found in the DNA trapped in nit cement from one of the mummies. The virus, discovered in 2008, is shed by healthy human skin and can on rare occasions get into the body and cause skin cancer. The discovery opens up the possibility that head lice could spread the virus.
A morphological analysis of the nits themselves also yielded information about the environment and migration pattern of their human host:
  • The mummies were all likely exposed to extremely cold temperatures when they died, which could have been a factor in their deaths. This was indicated by the very small gap between the nits and scalp on the hairs shaft. Lice rely on the host’s head heat to keep their eggs warm and so lay them closer to the scalp in cold environments.
  • Shorter cement tubes on the hair correlated with older and/or less preserved specimens, due to the cement degrading over time.
In the abstract to their open access paper published a few days ago in Molecular Biology and Evolution, the authors explain the significance of this discovery for the study of human evolution:
Over the past few decades there has been a growing demand for genome analysis of ancient human remains. Destructive sampling is increasingly difficult to obtain for ethical reasons, and standard methods of breaking the skull to access the petrous bone or sampling remaining teeth are often forbidden for curatorial reasons. However, most ancient humans carried head lice and their eggs abound in historical hair specimens. Here we show that host DNA is protected by the cement that glues head lice nits to the hair of ancient Argentinian mummies, 1,500–2,000 years old. The genetic affinities deciphered from genome-wide analyses of this DNA inform that this population migrated from north-west Amazonia to the Andes of central-west Argentina; a result confirmed using the mitochondria of the host lice. The cement preserves ancient environmental DNA of the skin, including the earliest recorded case of Merkel Cell Polyomavirus. We found that the percentage of human DNA obtained from nit cement equals human DNA obtained from the tooth, yield two-fold compared to a petrous bone, and four-fold to a bloodmeal of adult lice a millennium younger. In metric studies of sheaths, the length of the cement negatively correlates with the age of the specimens, while hair linear distance between nit and scalp informs about the environmental conditions at the time before death. Ectoparasitic lice sheaths can offer an alternative, non-destructive source of high-quality ancient DNA from a variety of host taxa where bones and teeth are not available and reveal complementary details of their history.

Clearly, this discovery is set to revolutionise our understanding of the recent evolution and migration patterns of modern humans. Whether it can be extended back to include suitably preserved archaic hominins such as Homo erectus, Neanderthals and Denisovans, remains to be seen. Either way, this is likely to be sending Creationist frauds into a frenzy of misrepresentation of the science in order to continue to fool their childish dupes and push the absurd notion that the Bible and Quran are biology and history textbooks.

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