What 'Kind' of Human is a Hybrid Human?

The fragment of bone from Denisova Cave seen from different angles.

Source: Brown, S. et al/CC BY 4.0

The genome of the offspring of a Neanderthal mother and a Denisovan father | Nature

The ever-developing story of the Homo sapiens who left Africa and migrated eventually to all parts of the world except Antarctica, just took another twist.

Geneticists at the Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany have shown that the greater than 50,000 year-old fragment of bone recovered from Denisova Cave in Siberia is of a female who died aged about 13 whose father was a Denisovan and whose mother was a Neanderthal. This fragment of bone had earlier been shown to be hominin by analysis of the fibrous structural protein, collagen and the mitochondrial DNA. The team who did this analysis had nicknamed her 'Denny'.

'Denny' is the first example of a first generation hybrid and the genetics are quite unambiguous. Of each pair of chromosomes, one was Neanderthal and the other was Denisovan and the mitochondrial DNA (from the mother) was Neanderthal.

The results were published two days ago in Nature.

Abstract
Neanderthals and Denisovans are extinct groups of hominins that separated from each other more than 390,000 years ago^1,2. Here we present the genome of ‘Denisova 11’, a bone fragment from Denisova Cave (Russia)³ and show that it comes from an individual who had a Neanderthal mother and a Denisovan father. The father, whose genome bears traces of Neanderthal ancestry, came from a population related to a later Denisovan found in the cave^4,5,6. The mother came from a population more closely related to Neanderthals who lived later in Europe^2,7 than to an earlier Neanderthal found in Denisova Cave⁸, suggesting that migrations of Neanderthals between eastern and western Eurasia occurred sometime after 120,000 years ago. The finding of a first-generation Neanderthal–Denisovan offspring among the small number of archaic specimens sequenced to date suggests that mixing between Late Pleistocene hominin groups was common when they met.

Slon, V., Mafessoni, F., Vernot, B., de Filippo, C., Grote, S., Viola, B., Hajdinjak, M., Peyrégne, S., Nagel, S., Brown, S., Douka, K., Higham, T., Kozlikin, M.B., Shunkov, M.V., Derevianko, A.P., Kelso, J., Meyer, M., Prüfer, K., Pääbo, S., 2018.
The genome of the offspring of a Neanderthal mother and a Denisovan father.
Nature. doi:10.1038/s41586-018-0455-x

© 2018 Springer Nature
Reprinted the with kind permission of Springer Nature under licence #4415390670008

We have know for some time now that Denisovans and Neanderthals interbred - the father of this child had some Neanderthal DNA from an earlier ingression in his ancestry. We have also known for some time that anatomically modern humans interbred with both, but these inter-species matings were believe to relatively rare. But this find suggests they may in fact have been relatively common. The thinking is statistical and of course, coincidence can't be ruled out, but of only 23 ancient hominins to have their DNA sequenced we now have this example of a first generation hybrid and another example, that of a member of our own species from 37,000 years ago who lived in modern Romania, 'Oase 1', who had a Neanderthal ancestor just four to six generations earlier.

With some 9% of known ancient hominins showing recent interbreeding, this suggests it may have been quite common. This in turn raises the possibility that these ancient cousin species of modern humans may not have gone extinct but were simply absorbed into the expanding and more numerous population of early modern H. sapiens. At a time when human groups were widely separated and mortality rates were high, finding a mate from amongst related species living nearby might have been a sensible strategy.

This adds to the picture of the hominin species forming a 'ring species' of partially diverged populations but with gene flow still possible between them due to frequent interbreeding. In other words, at that point in human evolution, divergence was still in progress; humans were at a stage where evolution had not progress to seperate species unable to interbreed but was still in progress.

So, which species committed creationism's mythical 'original sin' if we don't even have a single ancestral species? And what 'kind' of human is a hybrid human?

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