Guide to Patagonia's Monsters & Mysterious beings

I have written a book on this intriguing subject which has just been published.
In this blog I will post excerpts and other interesting texts on this fascinating subject.

Austin Whittall

Friday, May 11, 2018

Neanderthal and Denisovans split around 750 Kya

This paper: Early history of Neanderthals and Denisovans, by Alan R. Rogers, Ryan J. Bohlender, and Chad D. Huff (PNAS September 12, 2017. 114 (37) 9859-9863; published ahead of print August 7, 2017., has some interesting insights into Neanderthal diversity and population size. Below we quote from this paper

These results contradict current views about Neanderthal population history. For example, Prüfer et al. estimate that the Neanderthal population was very small—declining toward extinction. This view receives additional support from research showing elevated frequencies of nonsynonymous (and presumably deleterious) mutations among Neanderthals. This abundance of deleterious alleles implies that drift was strong and thus that population size was small. Yet our estimate of Neanderthal population size is large—in the tens of thousands."

So the authors find that the neanderthal population was large!. They then try to find common ground with other authors, adding:

"To reconcile these views, we suggest that the Neanderthal population consisted of many small subpopulations, which exchanged mates only rarely. In such a population, the effective size of the global population can be large, even if each local population is small. A sample from a single subpopulation would show a misleading signal of gradual population decline, even if the true population were constant. Furthermore, there is direct evidence of large genetic differences among Neanderthal populations. Finally, the rich and widespread fossil record of Neanderthals is hard to reconcile with the view that their global population was tiny. We suggest that previous research has documented the small size of local Neanderthal populations, whereas our own findings document the large effective size of the metapopulation that contributed genes to modern humans."

All of which makes perfect sense. They then address the timing of Neanderthal-Denisovan split:

"...As discussed above, our results also disagree with previous estimates of the Neanderthal–Denisovan separation time. On the other hand, Meyer et al. show that 430 ky-old fossils from Sima de los Huesos, Spain are more closely related to Neanderthals than to Denisovans. This implies an early separation of the two archaic lineages. Our own estimate—25,660 generations, or 744 ky—is earlier still. It is consistent with the results of Meyer et al. but not with those of Prüfer et al., as discussed above. The cause of this discrepancy is unclear. Prüfer et al. use the pairwise sequentially Markovian coalescent (PSMC) method, which may give biased estimates of separation times in subdivided populations..."

So they find a rather old (almost 750,000 years ago) split between Neanderthals and Denisovans.

In their introductory comments they mentioned some competing theories

"Around 600 kya, Europe was invaded by large-brained hominins using Acheulean stone tools. They were probably African immigrants, because similar fossils and tools occur earlier in Africa. They have been called archaic Homo sapiens, Homo heidelbergensis, and early Neanderthals, yet they remain mysterious. They may have been ancestors of Neanderthals and modern humans, or ancestors of Neanderthals only, or an evolutionary dead end. According to this last hypothesis, they were replaced later in the Middle Pleistocene by a wave of African immigrants that separated Neanderthals from modern humans and introduced the Levallois stone tool tradition to Europe."

Regarding the above, the authors write:

"Our results shed light on the large-brained hominins who appear in Europe early in the Middle Pleistocene. Various authors have suggested that these were African immigrants. This story is consistent with genetic estimates of the separation time of archaics and moderns. Our own results imply that, by the time these hominins show up in European archaeological sites, they had already separated from Denisovans. This agrees with Meyer et al., who show that the hominins at Sima de los Huesos were genetically more similar to Neanderthals than to Denisovans. It also agrees with Hublin, who argues that Neanderthal features emerged gradually in Europe, over an interval that began 500–600 kya."

And, they conclude:

"It appears that Neanderthals and Denisovans separated only a few hundred generations after their ancestors left the modern lineage. During the intervening interval, the Neanderthal–Denisovan lineage was small. After separating from Denisovans, the Neanderthal population grew large and fragmented into largely isolated local groups. The Neanderthal metapopulation that contributed genes to modern humans was much larger than the local population of the Altai Neanderthal fossil."

Denisovans admixed with Africans

Among their findings is corroboration of what we already know: "...yn is more common than xn —Neanderthals share more derived alleles with Europeans than with Africans. This suggests gene flow from Neanderthals into Europeans", and then, a startling finding: "More surprisingly, xd is more common than yd. The same pattern appears in all four combinations (YRI.CEU, YRI.CHB, LWK.CEU, and LWK.CHB) of African and Eurasian populations in our analysis. This pattern suggests gene flow from Denisovans into Africans..." (bold mine). This is unexpected: Denisovan admixture into Africans! Maybe it reflects an Out of Asia episode into Africa...

The fact that the Neanderthals were a large population split into sub-groups is very interesting because it is the opposite to what has been widely proclaimed until now: that they were a small, inbred group on the verge of vanishing when they mingled with modern humans...

Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2018 by Austin Whittall © 

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