Monday, 6 November 2017

Ancient Wisdom And Genetic Diversity

Neanderthal family group
Photo credit: Nikola Solic/Reuters/Newscom
Ancient genomes show social and reproductive behavior of early Upper Paleolithic foragers | Science

Two papers published a few days ago in the same edition of Science show that hunter-gatherer people, both modern human and Neanderthal, had evolved cultures which minimised the genetic risks inherent in inbreeding in the small bands of which these groups consisted.

Small groups consisting only of related extended families would have a very high probability of consanguinity and inherited recessive genes unless they had strategies for regularly introducing genetic material from other more distantly related groups.

Contrast this to the Biblical origin myths in which humans were twice supposedly breeding with siblings, cousins and other consanguineous, even other incestuous relationships. One of these would have been the immediate family of Adam and Eve (who were supposedly clones). The other was, of course, the small band of Ark survivors who not only had a barren and sterile planet to live on but also would have had major inbreeding problems to add to those they had already inherited from Adam and Eve's incestuous family. In neither of these cases, were they true, would there have been other groups from which to acquire a regular ingress of new genetic material.

This degree of inbreeding would lead quickly to the extinction of the species as we can see in, for example, the Spanish royal house of Hapsburg which became so highly inbred over a few generations that it fizzled out with the heirless death of the functionally, if not actually, sterile Charles II of Spain. He was severely both physically and mentally handicapped to the extent that he was declared Rex in Absentia and his mother ruled as Regent. His nickname was Carlos el Hechizado – Charles the Hexed, or Bewitched.

Charles II's maternal grandmother was also his father's sister - his father having married his own niece. His great-great-great-grandmother, Anna of Hapsburg was also his great-great-aunt, his great-great-great-aunt and his great-great-great-great-grandmother not once, but twice. Six generations should contain 62 different people; Charles II of Spain's contained just 32. Eight generations should contain 254 people; Charles II's contained 82. The poor kid never stood a chance.

For more on this see Rutherford, Adam. A Brief History of Everyone Who Ever Lived: The Stories in Our Genes (Kindle Locations 2424-2425). Orion. Kindle Edition..

This genetic disaster took just about 200 years to create. Imagine what would have happened to the two Biblical 'founder populations' who started out with far less diversity than did the Hapsburgs.

But anyway, these papers deal with a time in fairly recent human history when, according to Bible literalists, neither humans nor Earth actually existed. The first presents evidence that Upper Palaeolithic hunter-gatherer people lived in small groups groups with limited interbreeding but that the group existed within a wider social network from which breeding partners were frequently selected. Adolescents of both sexes appear to have frequently moved into an associated group within this social network. In effect, many young people went to live with their in-laws or at least in their in-laws social group.

This is based on an analysis of a small group of modern humans who lived 33,000 to 35,000 years ago at Sunghir in western Russia.

Present-day hunter-gatherers (HGs) live in multilevel social groups essential to sustain a population structure characterized by limited levels of within-band relatedness and inbreeding. When these wider social networks evolved among HGs is unknown. To investigate whether the contemporary HG strategy was already present in the Upper Paleolithic, we used complete genome sequences from Sunghir, a site dated to ~34,000 years before the present, containing multiple anatomically modern human individuals. We show that individuals at Sunghir derive from a population of small effective size, with limited kinship and levels of inbreeding similar to HG populations. Our findings suggest that Upper Paleolithic social organization was similar to that of living HGs, with limited relatedness within residential groups embedded in a larger mating network.

The second paper shows that Neanderthals too had a very similar social network. This is based on a new analysis of the genome of a Neanderthal female from about 50,000 - 65,000 years ago from Vindija Cave, Croatia. This contradicts what was thought from the previous best Neanderthal genome from a Neandertal woman from the Altai Mountains in southern Siberia. This showed a very high degree of inbreeding in that population. Her parents were half-siblings and her background level of genetic diversity was much lower than that of modern humans, suggesting a prolonged period of inbreeding.

Of course, there is no reason that both these situations could not arise in different parts of Eurasia as some groups could have become so isolated that they rarely encountered another group.

To date, the only Neandertal genome that has been sequenced to high quality is from an individual found in Southern Siberia. We sequenced the genome of a female Neandertal from ~50,000 years ago from Vindija Cave, Croatia, to ~30-fold genomic coverage. She carried 1.6 differences per 10,000 base pairs between the two copies of her genome, fewer than present-day humans, suggesting that Neandertal populations were of small size. Our analyses indicate that she was more closely related to the Neandertals that mixed with the ancestors of present-day humans living outside of sub-Saharan Africa than the previously sequenced Neandertal from Siberia, allowing 10 to 20% more Neandertal DNA to be identified in present-day humans, including variants involved in low-density lipoprotein cholesterol concentrations, schizophrenia, and other diseases.

It shouldn't be surprising that two different human species evolved cultures which converged on the same solution to the same problem. There was obvious selection pressure to favour cultures which set up these types of social networking and exchanged adolescents frequently. Cultures which discouraged or prohibited it would probably have become quickly extinct for the same reason the Hapsburgs did, vacating their territory for those groups which were less exclusive.

Memetic evolution, which takes place within cultures, worked to compensate for a problem for genetics caused by human dispersal as small hunter-gatherer groups. This cultural tendency to form social networks later facilitated the establishment of settled trading communities and urbanisation based on agriculture.

The interesting thing here, apart from the evidence of a wide social network in Neanderthals in the Balkans is that this group appear to be much closer to those with whom anatomically modern humans are known to have interbred. Indeed, interbreeding with moderns could indicate that moderns were on the edge of this social network. But this is also probably a much closer genomic analysis of a 'typical' Neanderthal and one from the population with whom we interbred, so it provides a much better basis for determining which Neanderthal genes non-African people still carry and how they contributed to our phenotype.

It would be surprising if there wasn't now a spate of papers reassessing how much of our genome is Neanderthal and probably finding it's more than we thought.

None of this would have been possible until a few years ago when techniques for extracting and analysing ancient DNA were developed - techniques that are improving and being refined, as well as becoming far less expensive. As this science develops and more and more of these discoveries are made, the chasm between what the primitive superstitions related in the Bible say and what reality shows is becoming ever wider. Ironically, the small bands of Canaanite hill farmers who adopted these Mesopotamian origin myths were almost certainly managing there own genetic diversity in this way or they would have gone extinct long before they wrote them down and showed they had no understanding of the problem their culture had evolved to solve.

It's surprising even that some people are still managing to keep a foot on either side of this widening chasm.

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