Following up on my previous post, I want to share some more papers on the subject of the admixture of Homo sapiens and archaic hominins in Africa, which may be the cause of the "genetic diversity" which is the main evidence supporting an African origin of modern humans.
This paper (Genetic evidence for archaic admixture in Africa, by Michael F. Hammera, August E. Woernera, Fernando L. Mendezb, Joseph C. Watkinsc, and Jeffrey D. Walld) reached the following conclusions:
"Extensive simulation results reject the null model of no admixture and allow us to infer that contemporary African populations contain a small proportion of genetic material (˜2%)
that introgressed ˜35 kya from an archaic population that split from the ancestors of anatomically modern humans ˜700 kya."
...
"Th[is] suggests that one such introgression event may have taken place in central Africa (where there is a very poor fossil record). Interestingly, recent studies attest to the
existence of Late Stone Age human remains with archaic features in Nigeria (Iwo Eleru) and the Democratic Republic of Congo (Ishango)"
The authors cite This paper (Allsworth-Jones, P., Harvati, K. and Stringer, C. (2010) The archaeological context of the Iwo Eleru cranium from Nigeria and preliminary results of new morphometric studies. In: Allsworth-Jones, P., (ed.) West African Archaeology New developments, new perspectives. BAR, S2164 . Archaeopress , pp. 29-42. ISBN 978 1 4073 0708 4):
""... results highlighted apparent archaic aspects in the specimen in its long and rather low cranial shape, and although modern overall, it also resembled fossils such as Omo Kibish 2 and Ngandong in certain respects. New studies... establish the relatively archaic shape of the vault, and confirm that this Late Stone Age individual was markedly different from succeeding populations.".
So we have archaic humans living relatively recently, and, the recent studies on Homo naledi also show that it was contemporary to the earliest modern humans (but it did not live -as far as we know in Central or Western Africa, but in South Africa:
In This paper we see that Homo naledi, is quite primitive but also relatively recent (The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa. Paul HGM Dirks. https://doi.org/10.7554/eLife.24231.001):
""We... establish[ed] that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity ... interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested ...: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/–70 ka, whilst a minimum age scenario yields an average age of 200 +70/–61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils... we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology."
In other words dating range from 139 to 414 ka but the authors selected intermediate dates. They too seem surprised by its archaic appearance at such a late date.
And it was indeed "archaic" as attested by this paper (Human Evolution: The many mysteries of Homo naledi, Chris Stringer) which says:
"...Berger et al. describe how the collection displays a unique combination of primitive and derived characteristics (Berger et al., 2015). For example, the small brain size, curved fingers and form of the shoulder, trunk and hip joint resemble the prehuman australopithecines and the early human species Homo habilis. Yet the wrist, hands, legs and feet look most like those of Neanderthals and modern humans. The teeth have some primitive features (such as increasing in size towards the back of the tooth row), but they are relatively small and simple, and set in lightly built jawbones. Overall, to my eye, the material looks most similar to the small-bodied examples of Homo erectus from Dmanisi in Georgia, which have been dated at ~1.8 million years old".
Interesting that H. naledi resembles more primitive Homo erectus with an age of 1.8 million years when it is only roughly 200 ka old!.
Another Paper (Genome Research Published in Advance February 17, 2016, doi: 10.1101/gr.196634.115 Model-based analyses of whole-genome data reveal a complex evolutionary history involving archaic introgression in Central African Pygmies, PingHsun Hsieh et al.) supports this idea of an archaic introgression, but this time, in Pygmies!:
"... our inference method rejects the hypothesis that the ancestors of AMH were genetically isolated in Africa, thus providing model-based whole genome-level evidence of African archaic admixture. Our inferences also suggest a complex human evolutionary history in Africa, which involves at least a single admixture event from an unknown archaic population into the ancestors of AMH (anatomically modern humans), likely within the last 30,000 yr."
These findings plus that of an early presence of Homo sapiens in Morocco - In this paper (New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens, Jean-Jacques Hublin et al. Nature 546, 289–292, 2017):
"...We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315?±?34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade..."
An age which clearly overlaps that of H. naledi
These findings may lead to an overhaul of the Out Of Africa theory as it is not implausible that H. sapiens originated in Eurasia or even America from other Out Of Africa migrants that departed long ago (Neanderthal ancestors or even H. erectus), and then they peopled Africa recently from North to South and mixed during their Into Africa journey with archaics like Naledi or Iwo Eluru, picking up genetic diversity and carrying it into sub-Saharan Africa with them.
Maybe archaic DNA will be recovered from Naledi and clarify the situation.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2017 by Austin Whittall ©
No comments:
Post a Comment