Tag Archives: human ancestry

Neanderthal news

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Increasingly sophisticated analysis of existing genomes from Neanderthal and Denisovan fossil bone, together with new data on single-chromosome DNA extracted from Croatian and Spanish Neanderthals continues to break new ground.

Artistic reconstruction of Neanderthal woman (credit: Natural History Museum, http://www.nhm.ac.uk/natureplus/blogs/tags/human_evolution)

Artistic reconstruction of Neanderthal woman (credit: Natural History Museum, http://www.nhm.ac.uk/natureplus/blogs/tags/human_evolution)

According to genome comparison between a Siberian specimen and modern humans, a population from which Neanderthals emerged separated from that which led to anatomically modern humans (AMH) sometime between 550 and 765 ka, although the fossil record can only confirm that divergence was before 430 ka. The comparison famously showed that Neanderthals contributed to modern, non-African humans between 47 and 75 ka, that is after the exodus of AMH from Africa that spread our species throughout all continents except Antarctica. This genetic exchange is thought to have taken place somewhere in the Middle East, which seems to have been a major staging post for our spread further east and also westward to Europe. A similar indication of liaison between Denisovans and AMH migrants is restricted to modern Melanesians, and probably took place in eastern Asia before 45 ka, when modern people began crossing from Eurasia to New Guinea and Australia. Neanderthal-Denisovan comparison suggests that those distinct groups separated between 380 and 470 ka ago (recently revised from an earlier estimate).

In both cases the gene flow was from the older groups to humans. Further examination of Siberian Neanderthal genomes now indicates that a reverse exchange occurred more than 100 ka ago (Kuhlwilm, M. and 21 others 2016. Ancient gene flow from early modern humans into Eastern Neanderthals. Nature, v. 530, p. 429-433). But the single-chromosome DNA from Croatian and Spanish Neanderthals shows no such sign This instance of two-way exchange is significant in another way: it took place before direct evidence of the generally accepted departure of African migrants to populate the rest of the world. At about 100 ka there is fossil evidence of possible AMH-Neanderthal cohabitation of the Levant, followed by a period with fossil evidence for Neanderthal presence there but not modern humans. Because stone tools from northern Arabia are dated as far back as 125 ka and closely resemble those associated with archaic modern humans, there is a possibility that AMH migration was far earlier than previously thought and passed through the Levant en route to points east.

Another tantalizing aspect of Neanderthal-modern human genetics is the tangible legacy of interbreeding with non-African humans. The first sign was that the gene (mc1r) that confers red hair on those of us blessed, or otherwise, with it may have Neanderthal origins, thus making us extremely proud of that heritage. The same gene is implicated in northern modern humans having developed pale skin, which might embarrass ‘white supremacists’! Similar studies in Svante Paabo’s lab at the Max Planck Institute for Evolutionary Anthropology in Leipzig also suggested 15 genome regions that include those involved in energy metabolism, possibly associated with type 2 diabetes; cranial shape and cognitive abilities, perhaps linked to Down’s syndrome, autism and schizophrenia; wound healing; skin, sweat glands, hair follicles and skin pigmentation; and barrel chests. There is more…

Joshua Akey of the University of Washington, Seattle, and evolutionary genomicist Tony Capra of Vanderbilt University in Nashville hit on the idea of ‘mining’ archived genetic information from more than 28 thousand living people for traces of 6000 Neanderthal DNA variants and comparing the results with physical traits and diseases logged in the human database (reported by Gibbons, A. 2016. Neanderthal genes linked to modern diseases. Science, v. 351, p. 648-9). On the plus side, Neanderthal ancestry may help boost immune responses to fungi, parasites and bacteria. Inheritance of enhanced blood coagulation, although greatly assisting recovery from wounds and hemorrhage when giving birth, confers a proclivity to heart attacks and strokes. Neanderthals also passed on ‘weak bladders’, solar keratoses that confer skin cancer risk, a tendency to malnutrition from modern diets low on meat and nuts, depression triggered by jet lag(!) and even a tendency to nicotine addiction. But a ‘pure’ line of modern human descent, shared by most Africans, also has its positive and negative heritable traits.

More on Neanderthals, Denisovans and anatomically modern humans

Snippets on human evolution

Image copyright held by author, Chris Henshilw...

Artifacts from the Blombos Cave, South Africa, including deliberately etched block of hematite Image by Chris Henshilwood via Wikipedia

The news that most humans outside of Africa carry fragments of DNA that match with those of Neanderthals and the mysterious Denisovan archaic humans ( see Yes, it seems that they did… and Other rich hominin pickings in the May 2010 issue of EPN) has entered into popular culture; or soon will have! Similar dalliances with the ‘older folk’ seem also to have occurred among those humans who remained in Africa (Hammer, M.F. et al. 2011. Genetic evidence for archaic admixture in Africa. Proceedings of the National Academy of Sciences, v. 108, p. 15123-15128). The DNA of three groups in West Africa who maintain a hunter-gatherer lifestyles show regions that are not involved in coding for proteins that differ from the African norm. This suggests mating with an entirely separate and unknown group of hominins – probably archaic forms of humans – that produced fertile offspring, probably around 35 thousand years ago. The find spurred re-evaluation of bones with a mix of archaic and modern features that were discovered in a Nigerian cave in the 1960s (Harvati, K. et al. 2011. The Later Stone Age Calvaria from Iwo Eleru, Nigeria: Morphology and Chronology. PLoS ONE, v.  6: e24024. doi:10.1371/journal.pone.0024024). The study confirms that the skulls are outside the fully modern human range, but display a close similarity with Neanderthal and H. erectus. The big surprise is that U-Th dating suggests they are quite recent, around 16 ka. The stage seems set for nor only a burst of exploration for human remains of less antiquity than early hominins but a ‘paradigm shift’ in our view of what constitutes a human species.

See also: Gibbons, A. 2011, African data bolster new view of modern human origins. Science, v. 334, p. 167.

Another interesting link with archaic humans who had the closest of relationships with some of our ancestors is that their union may have bolstered the resistance of migrants from Africa to Eurasian pathogens (Abi-Rached, L. and 22 others 2011. The shaping of modern human immune systems by multiregional admixture with archaic humans. Science, v. 334, p. 89-94). The focus was on the human leucocyte antigen (HLA) group that is a vital part of our immune system in the form of ‘killer cells’. Part of modern Eurasian DNA that codes for the group (HLA-B*73 allele) appears in the Neanderthal and Denisovan genomes; indeed more than half the HLA alleles of modern Eurasians may have originated in this way, and have also been introduced into Africans subsequently.

Also at the front line of genomic research into human origins, DNA sequenced from a lock of hair given to an Edwardian anthropologist by a native Australian turns out to have an extreme antiquity compared with that of other Eurasian people descended from African migrants (Rasmussen, M. and 57 others. An aboriginal Australian genome reveals separate human dispersals into Asia. Science, v. 334, p. 94-98). The unique aspects of the Australian genome signify separation of a group of individuals from the main African population around 62-75 thousand years ago; significantly earlier than and different from ‘run of the mill’ migrants from whom modern Asians arose at between 25 to 38 ka. There is little doubt that native Australians are descended from the pioneers who first diffused from Africa either by crossing the Straits of Bab el Mandab or taking another route and they moved more speedily across southern Asia than other waves made possible by climate change and sea-level falls following the Eemian interglacial of 133-115 ka.

Despite the lingering Eurocentrist view that somehow fully modern human consciousness sprang into being at the time the famous French and Spanish cave art was painted, around 30 ka, increasing evidence points to an African origin for a sense of aesthetics and the ability to express it. The latest is the discovery of a 100 ka ‘paint box’ in a South African coastal cave (Henshilwood, C.S. et al. 2011. A 100,000-year-old ochre-processing workshop at Blombos Cave, South Africa. Science, v. 334, p. 219-223). The material consists of two large abalone shells containing traces of red and orange ochre, together with a hammer stone and grinder with adhering ochre, and fat-rich bones which ground-up would have produced a binder for the ochre. No art occurs in the cave and it might be supposed that the pigments were intended for face- or body adornment.

Another candidate for earliest, direct human ancestor

The cranium of Malapa Hominid 1, Holotype of A...

The head of Australopithecus sediba. Image via Wikipedia

In May 2010 EPN commented on a new find from the famous fossil-rich caves of north-eastern South Africa; a new hominin species called Australopithecus sediba. At least one of them fell into a deathtrap shaft, died and remained unchewed without bones being spread far and wide. Inevitably, near-complete skeletons of individual hominins are soon pored over by dozens of specialists in human evolution, as they were for the much older Ardepithecus ramidus found in sediments of Ethiopia’s Afar Depression (see Early hominin takes over Science magazine in the November 2009 issue of EPN). Now there are two near-complete, well-preserved skeletons of Au. sediba and the palaeoanthropological world is agog. Dating to about 1.98 Ma the specimens represent the same time as do far less impressive remains of H habilis from Tanzania that were found with associated rudimentary stone tools. The first hint (just a fragment of upper jaw) of any remains that might be tagged ‘Homo’ dates to 2.3 Ma and is from Ethiopia, as are the first undoubted stone tools going back as far as 2.5 Ma, though lacking association with a maker.

Five consecutive papers on Au. Sediba occupy 22 pages in the 9 September 2011 issue of Science and make for startling reading. The first concerns the shape of its brain case, and therefore crudely its brain, discerned by tomographic X-ray scanning (Carlson, K.J. et al. 2011. The endocast of MH1, Australopithecus sediba. Science, v. 333, p. 1402-1407). It isn’t any bigger than that of other members of the genus but shows ‘some foreshadowing of the human frontal lobes’ and other shifts from the basic ape model that the authors imply are en route to human features. The next considers the two pelvis regions (Kibii, J.M. et al. 2011. A partial pelvis of Australopithecus sediba. Science, v. 333, p. 1407-1411); again australopithecine-like in the small size of the birth canal but with a hint of the S-shape of humans. Most astonishingly well-preserved are the fragile bones of a complete hand (Kivell, T.L.  et al. 2011. Australopithecus sediba hand demonstrates mosaic evolution of locomotor and manipulative abilities. Science, v. 333, p. 1411-1417), which convincingly shows the long thumb and short fingers (for a primate) that characterise Homo and are essential for a precision grip and making things. Actually, the thumb is longer relative to fingers (60%) than in humans (54%), but Lucy’s (Au. afarensis) was a closer match. No tools that such a hand might have created and wielded were found with the fossils. Then there is the foot (Zipfel, B. et al. 2011. The foot and ankle of Australopithecus sediba. Science, v. 333, p. 1417-1420), which, again, mixes human and australopithecine features, giving ‘a unique form of bipedality and some degree of arboreality’. The fifth paper (Pickering, R. et al. 2011. Australopithecus sediba at 1.977 Ma and implications for the origins of the genus Homo. Science, v. 333, p. 1417-1420) is as remarkable for the precision of U-Pb dating of speleothem (cave carbonates), which at 1.977+0.002 Ma far exceeds the workhorse Ar-Ar method used for most other hominins, as it is for the absolute age that precedes that of undisputed remains of humans.

In short, for Australopithecus sediba there is an embarrassment of riches unmatched until those of the 1.5 Ma old H. erectus (‘Turkana Boy’) found at Nariokotome in NW Kenya. To some extent this throws a flock of peregrines in among the palaeoanthropology pigeons, as an account of a meeting earlier in 2011, at which the bones were grandstanded, shows (Gibbons, A. 2011. Skeletons present an exquisite paleo-puzzle. Science, v. 333, p. 1370). Naturally, the authors are making the most of their material especially, it seems, its finder Lee Berger of the University of Witwatersrand, South Africa, the last author in all the papers. Comparisons with more australopithecine remains were said to be needed. The soon-to-be-famous hand has been said to be essentially like others from the same genus. While the remains of the creature’s pelvis could imply that its evolution was more driven by a need for efficient upright walking than to birth big-headed babies, the ankle shows a primitive trait that would have forced Australopithecus sediba to walk strangely as the heel bone is small and angled unlike that in human feet, which is broad and flat. But all the species’s features are combined in two near-complete individuals, whereas for the rest of its contemporaries, predecessors and near successors in time speculation is based on fragments of several individuals, none more so than in the case of the earliest agreed human, near contemporaneous H. habilis, which barely stands up to taxonomic scrutiny (Gibbons, A. 2011. Who was Homo habilis – and was it really Homo?  Science, v. 332, p. 1370-1371). Some would say that it was only the associated stone tools that assigned ‘Handy Man’ to more elevated status than slightly large-headed australopithecine. The fact is; stone tools were around since 2.5 Ma, at least in Ethiopia, and this newly found being could have handled them and even made them with its palpable dexterity. Finding tools and skeletons together is almost as rare as hens with teeth…