Wednesday, 24 June 2015

Early modern human from Romania had recent Neanderthal ancestor

Ancient DNA from Peştera cu Oase demonstrates inbreeding no more than four to six generations previously

The cave site of Peştera cu Oase (‘Cave with Bones’) in Romania has yielded some of the earliest fossil remains of modern humans in Europe. The remains of three individuals recovered from the site include a largely-complete lower jawbone (Oase 1), the near-complete skull of a 15-year-old adolescent, and a left temporal bone. The remains are around 40,000 years old and exhibit a mosaic of modern and archaic features. Modern features include the absence of browridges, a narrow nasal aperture, and a prominent chin; but there are also archaic features such as a wide dental arcade and very large molars. There is little doubt that they are modern humans and not Neanderthals, but some aspects of the morphology are consistent with Neanderthal ancestry.

Researchers have now recovered ancient DNA from the Oase 1 jawbone and sequenced the genome. They report that between 6 to 9 percent of the genome is of Neanderthal origin, a higher percentage than for any other modern human genome sequenced to date. Three chromosomal segments of Neanderthal DNA are of considerable length, suggesting that the Neanderthal contribution to the Oase 1 individual occurred so recently in their past that the chromosomal segments of Neanderthal origin had little time to break up due to recombination. The researchers turned their attention to seven segments of the genome that appeared to be of recent Neanderthal origin and from the genetic lengths of these, implied that Oase 1’s Neanderthal ancestor had lived no more than four to six generations earlier, or less than two hundred years.

The existence of such a recent Neanderthal ancestor casts doubts on theories that suggest that interbreeding occurred only very occasionally, or was confined to an early episode soon after modern humans first left Africa. However, the researchers failed to establish a clear relationship between the Oase 1 individual and later modern humans in Europe, suggests that they may have been a member of an early modern human population in Europe that eventually died out without contributing much to later European populations.

Reference:
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Fu, Q. et al., An early modern human from Romania with a recent Neanderthal ancestor. Nature 524, 216-219 (2015).

Friday, 19 June 2015

Kennewick dispute set to reignite

Ancient DNA confirms Native American affinities

Kennewick Man died about 8,600 years ago and was between 40 to 55 years old at the time of his death. In 1996, his skull and some other skeletal parts were discovered in the Columbia River, Kennewick, Washington State. The find was of interest not just to anthropologists but also to Native Americans, who refer to him as the Ancient One. The Plateau people of the Pacific Northwest claimed an ancestral relationship and requested repatriation of the remains as provided for under US federal law (Native American Graves Protection and Repatriation Act or NAGPRA). The land where the remains were found is managed by the US Army Corps of Engineers, who announced that they were willing to hand over the remains. This in turn precipitated a lawsuit from scientists wishing to study the remains.

The plaintiffs’ claim was based on the morphology of the skull, which is long and narrow, with a narrow face, and a jutting chin. It is quite unlike the broad-headed, broad-faced appearance typical of Native Americans and resembles that of certain Pacific populations, in particular the Ainu and Polynesians. It was argued that Kennewick Man belonged to a population that reached America before the ancestors of the present-day Native Americans, and that the request for repatriation of the remains must therefore be rejected. In 2004, the plaintiffs’ claim was upheld by a judicial ruling.

However, subsequent discoveries have cast doubt on the claim that Native Americans are descended from migrants that replaced an earlier American population. Remains have been found that are even older than those of Kennewick Man, yet fall comfortably within the morphological range of present-day Native Americans. Other remains have yielded mitochondrial DNA belonging to haplogroups only found in Native American populations. Genetic studies have failed to find any evidence for a replacement of early Paleoindians by ancestors of today’s Native Americans.

It has been suggested that skull data has simply been misinterpreted. In one study, researchers applied statistical methods to skulls from all over the world, dating from around 15,000 years ago to the present day. They found that when shape variation was considered over a wide geographical range or over a long period of time, the skulls formed a continuum rather than discrete categories. The same pattern was also seen when New World skulls were considered on their own. The supposed Paleoindian and Native American forms were no more than extremes at opposite ends of a continuum, and most of the New World skulls fell well between the two extremes.

Following the 2004 ruling, study of Kennewick Man continued, but only now have researchers obtained ancient DNA from the remains. A team led by Morten Rasmussen has published its results in the journal Nature and they show that Kennewick Man is more closely related to present-day Native Americans than to any other population worldwide. Based on a comparison with Native American groups for whom genome-wide data is available, several groups are apparently descended from population closely related to that of Kennewick Man, including the Confederated Tribes of the Colville Reservation (Colville), which is one of the five groups claiming Kennewick Man.

A renewed claim for repatriation now seems inevitable.

References:
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1.
Rasmussen, M., Sikora, M., Albrechtsen, A., Korneliussen, T. & Moreno-Mayar, J., The ancestry and affiliations of Kennewick Man. Nature 523, 455-458 (2015).
2.
Jantz, R. & Owsley, D., Variation Among Early North American Crania. American Journal of Physical Anthropology 114, 144-156 (2001).

Thursday, 18 June 2015

Did Aboriginal Australians rediscover boats after over 20,000 years?

Evidence for human activity on island in ancient mega-lake

Lake Mungo is the largest of a series of 19 now dried up lakes making up the Willandra Lakes system. The region is a World Heritage Site covering 2,400 sq. km (925 sq. miles) in southwest New South Wales, about 1,000 km (620 miles) west of Sydney. The water levels in the lakes remained high until 45,000 years ago and then began to decline. They dried up completely 22,000 years ago, and have remained dry ever since. However, a recent survey has shown that 24,000 years ago, Lake Mungo underwent a sudden massive filling episode, increasing its depth by 5 m (16 ft.) and its volume by 250 percent. Lake Mungo became linked to its neighbour, Lake Leaghur, at two overflow points, so creating an island in between.

Humans arrived in the Lake Mungo region at least 20,000 years before the mega-lake phase. The expansion of Lake Mungo would have substantially affected mobility, forcing people to skirt the mega-lake. However, the presence of hearths and stone artefacts on the island suggests that they repeatedly crossed the inflow channel, taking stone tools and hunting equipment with them. While they could have swum, using bags to carry tools, it is likelier that they used boats.

This implies a highly flexible response to the sudden change in conditions, and possibly a re-discovery of boat technology. While Aboriginal Australians must have used boats to reach Australia in the first place, there is a lack of evidence for pelagic fishing and navigation to offshore islands around the Australian coast until a few thousand years ago. It has accordingly been assumed that watercraft technologies were abandoned after initial arrival and dispersal across Australia. If boats were used to cross Lake Mungo during its expanded phase 24,000 years ago, then this represents the revival of a technology which had apparently been abandoned over 20,000 years earlier, and at a location well inland and far from any major navigable rivers.

Reference:
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Fitzsimmons, K., Stern, N., Murray-Wallace, C., Truscott, W. & Pop, C., The Mungo Mega-Lake Event, Semi-Arid Australia: Non-Linear Descent into the Last Ice Age, Implications for Human Behaviour. PLoS One 10 (6), e0127008 (2015).x