Prehistory of New World Arctic investigated in major new genetic study

Paleo-Eskimos were independent of Inuit and Native American expansions

In the 1980s, the American linguist Joseph Greenberg proposed that Native American languages could be classified within three families: Eskimo-Aleut, Na Dene and Amerind. He further suggested that each family corresponded to a separate migration into the New World from Siberia and concluded, therefore, that the New World had been peopled by three migrations. Greenberg’s views remained controversial for many years as most mitochondrial and Y-chromosomal genetic studies indicated that there had been no more than two migrations. In 2012, however, he was apparently vindicated when David Reich and his colleagues presented a high resolution study of 52 Native American and 17 Siberian groups genotyped at 364,470 single nucleotide polymorphisms. The results indicated that there had indeed been three migrations broadly corresponding to the three language families: specifically (i) First Americans, (ii) Eskimo-Aleuts and, (iii) Saqqaq and Na Dene speakers.

These results are built on by a major new study conducted by an international team numbering over fifty researchers led by geneticist Maanasa Raghavan from the University of Copenhagen. The study focussed on mitochondrial and genome-wide sequences obtained from ancient bone, hair and teeth samples of Arctic Siberia, Alaska, Canada, and Greenland, and high-coverage genomes of two present-day Greenlandic Inuit, two Siberian Nivkhs, one Aleutian Islander, and two Athabascan Native Americans.

From this data, researchers hoped to resolve issues regarding the complex archaeological record of the Early Paleo-Eskimos (Pre-Dorset/Saqqaq), the Late Paleo-Eskimos (Early Dorset, Middle Dorset, and Late Dorset), and the Thule cultures. They were able to show that the Paleo-Eskimos reached the New World in a single migration from Siberia around 3000 BC and displayed genetic continuity for more 4,000 years. About 700 years ago they were replaced by the Thule people, who were the ancestors of the present day Inuit.

While supporting Reich et al overall, the results indicated that the Saqqaq tradition and Na Dene speakers were not part of the same migratory wave: accordingly the Paleo-Eskimos must have arrived in a separate migration to the three waves identified by Reich et al, implying that the New World was populated by four migrations in all.

References:

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1.  Reich, D. et al., Reconstructing Native American population history. Nature 488, 370–374 (2012).

2.  Greenberg, J., Turner, C. & Zegura, S., The Settlement of the Americas: A Comparison of the Linguistic, Dental, and Genetic Evidence. Current Anthropology 27 (5), 477-497 (1986).

3.  Raghavan, M. et al., The genetic prehistory of the New World Arctic. Science 345 (620), 1020,1255832 (2014).

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Neanderthals coexisted with modern humans for up to 5,000 years

New radiocarbon dates point to longer coexistence but earlier extinction

A new study published in the journal Nature suggests that Neanderthals persisted alongside modern humans in Europe for as long as 5,000 years after the arrival of the latter. A team lead by Tom Higham at Oxford obtained 196 AMS radiocarbon dates from 40 sites across Europe, relying on improved techniques to remove young carbon contamination. The results also indicate that the Neanderthals were probably extinct no later than 41,000 to 39,000 years ago.

Although it was once believed that Neanderthals and modern humans had coexisted for up to 10,000 years, work in the middle of the last decade suggested that the overlap was very brief.  The new results represent a reversion to the earlier position, albeit pushed further back in time since it is now believed that modern humans first reached Europe about 46,000 years ago (Higham’s team suggest the date was around 45,000 years ago).

The new dates may resolve long-running controversy over the Châtelperronian culture, with is believed to be of Neanderthal origin but incorporates elements associated with modern human behaviour. The dates indicate that the Châtelperronian began around 45,000 years ago, suggesting that it was influenced by interaction with modern humans. The Châtelperronian comes to an end at about the same time as the Mousterian, about 41,000 to 39,000 years ago

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The researchers were unfortunately unable to obtain any dates for remains from Gorham’s Cave, Gibraltar, where Neanderthal survival after 30,000 years ago has been claimed.

The lengthy overlap rules out the in any case improbable hypothesis that modern humans hunted down and exterminated the Neanderthals. It is more likely that a combination of increased competition for limited resources and the Heinrich Event 4 climatic downturn 40,000 years ago was responsible.

References: 

Higham, T. et al., The timing and spatiotemporal patterning of Neanderthal disappearance. Nature 512, 306-309 (2014). 

Gibraltar Neanderthals ate roasted pigeons

Further evidence of Neanderthal sophistication at Gorham’s Cave

Gorham’s Cave, Gibraltar, was occupied by Neanderthals for thousands of years and was one of the last known sites of Neanderthal occupation before their final disappearance. Researchers have been working at the cave site for the past 25 years, and it has yielded a wealth of data about Neanderthal technology and patterns of subsistence.

In a survey published online in Nature Scientific Reports, researchers examined 1,724 Rock dove (common pigeon) bones from the cave, spanning the period from 67,000 to 28,000 years ago. All but the most recent part of this time period is associated with Mousterian technology, implying that the occupants of the cave at that time were Neanderthals. Modern human Upper Palaeolithic technology does not appear until near the end of the sequence.

Some of the bones were unevenly discoloured, consistent with roasting over a fire or glowing embers. Bones with less meat on them would have been more intensely affected by the heat, and would consequently undergo more discoloration than meatier bones. Some bones also displayed cut marks and/or tooth marks.

The exploitation of the pigeons was not sporadic: there is repeated evidence for the practice throughout the time that Neanderthals were resident in the cave. Furthermore, they could not have learned about it from modern humans as the earlier evidence substantially predates the arrival of modern humans in Europe.

That the Gorham’s Cave Neanderthals were able to regularly exploit this reliable and sustainable source of food is further evidence of their sophistication.

References:

1. Blasco, R. et al., The earliest pigeon fanciers. Nature Scientific Reports online (2014).

Link:
http://www.nature.com/srep/2014/140807/srep05971/full/srep05971.html

Is Homo floresiensis a valid species?

New papers revive ‘hobbit’ controversy

The announcement in 2003 that dwarf hominins had been discovered at Liang Bua Cave on the Indonesian island of Flores was one of the major news stories of that year. The type specimen, LB1, a female inevitably dubbed ‘Flo’ had lived had lived just 18,000 years ago at a time when all archaic hominins were believed to be long extinct. Estimated to have been around thirty years old at the time of her death, ‘Flo’ stood just 1.06 m (3 ft. 6 in.) tall, weighed 16 and 36 kg (35 and 79 lb), and had an estimated cranial capacity of just 380 cc, comparable to that of an australopithecine.

Rapidly dubbed the ‘hobbit people’ on the grounds of their diminutive stature, the hominins were recognised as a new human species, Homo floresiensis. It was suggested that in the absence of natural enemies on an island where food is fairly scarce, ‘Flo’s’ people had undergone a process known as insular dwarfism, where smaller individuals are positively selected for and over several generations, the entire population ‘downsizes’.
Not everybody accepted this explanation. In 2006, the late Teuku Jacob claimed that Flo was a modern human of Australomelanesian extraction, who had suffered from a developmental disorder leading to a smaller brain known as microcephaly. Jacob found little support for his views and was also criticised for allegedly damaging the specimens while they were on loan to him from the Indonesian National Archaeological Research Center.

The controversy had been revived by the publication of two companion papers in the journal PNAS. Two of the authors of these new papers were also involved with Jacob’s original study. The first paper, Henneberg, et al (2014), argues that Flo was suffering from Down syndrome. This can result in atavism, where developmental characteristics of an earlier ancestral condition appear alongside undisrupted characteristics. This pattern could explain what has been otherwise interpreted as a mosaic of primitive and derived features. As a teratological specimen, the authors note that LB1 is not eligible to be designated the type specimen of a new species.

In the second paper, Eckhardt, et al (2014) suggest that based on an examination of the Flores specimens made in 2005, both the stature and brain size of LB1 have been underestimated. LB1, they argue, possessed abnormalities such as craniofacial asymmetry and a thigh bone disproportionately short in relation to its other long bones. Such abnormalities are indicative of Down syndrome and a number of other developmental conditions.

 References:
1. Jacob, T. et al., Pygmoid Australomelanesian Homo sapiens skeletal remains from Liang Bua, Flores: Population affinities and pathological abnormalities. PNAS 103 (36), 13421–13426 (2006).
2. Henneberg, M., Eckhardt, R., Chavanaves, S. & Hsüc, K., Evolved developmental homeostasis disturbed in LB1 from Flores, Indonesia, denotes Down syndrome and not diagnostic traits of the invalid species Homo floresiensis. PNAS (Early Edition) (2014).
3. Eckhardt, R., Henneberg, M., Weller, A. & Hsüc, K., Rare events in earth history include the LB1 human skeleton from Flores, Indonesia, as a developmental singularity, not a unique taxon. PNAS (Early Edition) (2014).

Links (all papers are open access):
Jacob, et al http://www.pnas.org/content/103/36/13421.short
Henneberg, et al http://www.pnas.org/content/early/2014/07/31/1407382111.abstract
Eckhardt, et al http://www.pnas.org/content/early/2014/07/31/1407385111.abstract

Craniofacial changes after 80,000 years ago may reflect increased social tolerance

Did technology boom result from reduced male aggression?

An ambitious study published in the journal Current Anthropology has proposed a link between craniofacial changes and technological advances occurring after around 80,000 years ago. The authors suggest that a reduction in browridge projection and a shortening of the upper facial skeleton (referred to by the authors as ‘feminization’) was the result of either reduced testosterone levels or reduced androgen receptor densities. This reduced male aggression and increased social tolerance, in turn enabling larger groups to live together and the building of long-distance social networks. The consequence was that between around 80,000 and 30,000 years ago, there was acceleration of cumulative technological evolution or ‘cultural ratcheting’ where innovations accumulate over time as a result of cooperation between individuals and groups.

Robert Cieri and his colleagues considered over 1,400 skulls from prehistoric people living before and after 80,000 years ago, and from recent foragers and farmers. They found that a trend towards browridge reduction and facial shortening is apparent from after 80,000 years ago, consistent with the hypothesised higher testosterone levels or androgen receptor densities prior to that time.

The study is the latest attempt to resolve an apparent lag in the archaeological record between the appearance of anatomically modern humans and clear evidence for modern human behaviour in the form of symbolic expression, innovation and planning depth. Such evidence does not become apparent until after 80,000 years ago, leading some anthropologists to postulate a ‘smartness mutation’ occurring at about that time that somehow ‘rewired’ the human brain and enabled it function far more efficiently.

In the last fifteen years or so, the trend has been to look for demographic rather than cognitive explanations. The African Middle Stone Age has examples of seemingly precocious technological traditions such as Stillbay and Howieson’s Poort that were relatively short-lived and were replaced by more conservative traditions. It is argued that periodically, population levels fell to below the level needed to preserve the complex technological traditions from one generation to the next. It has also been suggested that evidence for symbolic behaviour in the form of beads and ornaments is indicative of more complex societies rather than more complex brains. Both fit well with the idea of more tolerant societies emerging after 80,000 years ago.

However, the most recent archaeological data has failed to correlate the disappearance of advanced technological traditions with demographic collapse, and indeed the extent to which such technologies were repeatedly lost has been questioned. For example, microliths are now known to have first appeared 165,000 years ago and their periodic disappearance from the archaeological record may be apparent rather than actual.    

References:

1. Cieri, R., Churchill, S., Franciscus, R., Tan, J. & Hare, B., Craniofacial Feminization, Social Tolerance, and the Origins of Behavioral Modernity. Current Anthropology 55 (4), 419-443 (2014).