Wednesday, 30 September 2015

Congenital defect is possible further evidence of inbreeding by Neanderthals at El Sidrón

High incidence of congenital clefts of the arch of the atlas observed among remains from Spanish site

The Atlas (C1) vertebra is the first cervical vertebra of the spine, immediately below the skull. It takes its name from the Greek Titan Atlas, who is popularly (but incorrectly) supposed to have held the world on his shoulders. Congenital defects of the anterior or posterior arches are rare in modern populations, occurring at frequencies of 0.087 to 0.1 percent and 0.73 to 3.84 percent respectively. The condition does not normally lead to clinical symptoms.

El Sidrón is a cave site in Asturias, northern Spain that has yielded extensive Neanderthal remains and stone tools since these were first discovered there in 1994. Over 2,400 human fossils have been recovered, representing at least thirteen individuals including seven adults, three adolescents, two juveniles and one infant. The remains are 49,000 years old. Ancient DNA has previously been obtained from the remains, indicating a small patrilocal (mature males remain within their family birth group, but females come from outside) group with low genetic diversity. Dental hypoplasias indicate that around half of the group members had experienced episodes of growth arrest due to malnutrition.

Researchers now report that two out of just three well-preserved atlases from the site present respectively a defect of the posterior arch and the anterior arch. Such a high incidence of a rare condition could be interpreted as further evidence of low genetic diversity of the group, and as a possible indicator of inbreeding. The picture that emerges from El Sidrón is of a small, barely-viable Neanderthal group struggling for survival in extremely harsh conditions.

:Ríos, L. et al., Possible Further Evidence of Low Genetic Diversity in the El Sidrón (Asturias, Spain) Neandertal Group: Congenital Clefts of the Atlas. PLoS One 10 (9), e0136550. (2015).

Friday, 11 September 2015

Hitherto-unknown early human species discovered deep inside Rising Star Cave, South Africa

A team led by Lee Burger has announced the discovery of a new species of early human.

Professor Berger, an American palaeoanthropologist working at the University of the Witwatersrand, Johannesburg, is known for Australopithecus sediba, announced in 2010 and at the time was the first new hominin species to be discovered in South Africa for decades. The discovery was when Matthew, Lee’s nine-year-old son, discovered a hominin collar bone embedded in a rock at Malapa, part of a now-eroded cave system near to Sterkfontein and Swartkrans, where many important hominin finds have been made.

Berger felt other cave systems in South Africa had the potential to yield hominin fossils, so in 2013 he recruited a team of cavers to search the Rising Star cave system, 50 km (30 miles) northwest of Johannesburg. The cave has been well explored over the years, but the team came across a narrow 18 cm (7 in.)-wide shaft that dropped vertically for 12 m (39 ft.) into an unexplored chamber. The cavers descended into the chamber and saw a fossil skull and jawbone lying on the floor of the cave. Berger believed that there were hominin fossils and obtained funding from the National Geographic for an expedition.

But to access what became known as Dinaledi Chamber (‘chamber of stars’) was problematic. Before they could even reach the narrow shaft leading down to the chamber, researchers, researchers would have to pass through another tiny shaft known as Superman’s Crawl and then climb a steep section known as Dragon’s Back. Berger placed an advertisement on Facebook for ‘small, skinny’ scientists believing at best there might be three or four people in the world who would fit the criteria. In the event, within days 57 suitable candidates had applied from which he chose six, all women. Within a month, the Rising Star Expedition had set up camp at the cave system and excavations commenced. Working in six-hour shifts, the six women soon recovered more fossil material than had been found in the whole of South Africa in the previous 90 years. Meanwhile, back on the surface, a large team began preparing and cataloguing the fossils, making full use of social media to report progress. A total of 1,550 fossils were recovered, comprising 15 individuals, including males, females and infants.

Berger then invited thirty young postdoctoral researchers from fifteen countries to help him evaluate the haul at a workshop in Johannesburg. They were accompanied by twenty of Berger’s more senior colleagues, who had worked with him on the Australopithecus sediba discovery. This unusual move did not please everybody and some questioned the wisdom of handing over such important fossils to inexperienced researchers.

The findings have now been announced. The remains represent a new human species, Homo naledi, named for the word ‘star’ in the local Sotho language. The new species is comparable in height and weight to a small-bodied modern human or a large australopithecine, with an estimated stature of around 1.5 m (5 ft.) and weighing 40 to 55 kg (88 to 121 lb.). The brain is tiny, ranging from 465 to 560 cc, overlapping entirely with the range of values known for australopithecines. The reconstructed skeleton exhibits both humanlike and apelike features, but in a combination that has not been seen with other hominins. The feet and lower limbs are humanlike, but the upper thighbone, pelvis and shoulders are apelike. The hands and wrists are humanlike, though the fingers are curved suggesting that it spent some of its time in the trees as well as on the ground. Overall, Homo naledi is the most primitive, small-brained hominin ever to have been included in Homo, but the shape of cranium and lower jawbone and the dentition suggest that it is human rather than an australopithecine.

Unfortunately, no dates have yet been published for the fossils. They are presumably too old to be radiocarbon dated, but there is no readily-datable material in the chamber. Calcium carbonate flowstones have been found to have been contaminated with materials from associated muds, making them unsuitable for uranium series dating. All we currently have to go on is the primitive characteristics such as the small brains. These suggest that Homo naledi emerged close to the base of the human family tree 2.5 to 2.8 million years ago. But until we have dates for the fossils, or other fossils turn up that can be dated, it will be difficult to say just where Homo naledi fits into the overall picture of human evolution.

Also troublesome is the question of how the fossils reached Dinaledi Chamber in the first place. There is a near-absence of non-hominin fossils in Dinaledi Chamber – yet these are abundant in the adjacent Dragon’s Back. This rules out the remains having being swept into Dinaledi Chamber by a flash flood, as this would have left a mixture of hominin and non-hominin remains in both chambers. Carnivores are also ruled out: even if there was a carnivore that preyed exclusively on Homo naledi, why would it drag its prey into such an inaccessible location? In any case, none of the bones showed any evidence of having been gnawed by carnivores. Nor does it seem that the hominins fell down a shaft leading into the cave from the surface: there is no evidence that any such shaft had ever existed. The fossils accumulated over time, so it can also be ruled out that a single group entered the chamber for some reason and then become trapped there.

The only obvious explanation is that the remains were deliberately placed in the chamber as part of a post-mortem ritual, although there is no evidence for such rituals until much later. Mass deposition of corpses is first seen at the cave site of Sima de los Huesos in Spain, 430,000 years ago. Even this was nothing more than a hygienic disposal of the corpses rather than any form of ritual. Also, unlike Homo naledi, the brain size of the Sima people was only slightly below that of modern people. In any case, even hygienic disposal seems unlikely as there is no evidence that Rising Star was ever inhabited, and there would surely be no need to use such an inaccessible chamber.

Taken at face value, the evidence from Dinaledi Chamber suggests that early humans were far more behaviourally complex than has long been believed. However, it is probably too soon to jump to conclusions and all that can safely be said is that we don’t yet know how the fossils reached the cavern.


1. Berger, L., Hawks, J., de Ruiter, D. & Churchill, S., 2015. Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. eLife.
2. Dirks, P. et al., 2015. Geological and taphonomic context for the new hominin species Homo naledi from the Dinaledi Chamber, South Africa. eLife.

Thursday, 3 September 2015

Radiocarbon dates used to trace possible origins of domesticated rice

Seven models tested against extensive archaeological database

Rice is one of the world’s most important cereal crops, and has supported dense human populations in Asia since Neolithic times. The origin and spread of domesticated rice is understandably of great interest to students of Asian prehistory and researchers have employed a variety of methods, including genetics, phytolith studies, from the presence of charred grains in archaeological excavations, and from rice husks in Neolithic pottery.

In a newly-published study researchers have made use of an extensive database of radiocarbon data from 400 sites spanning 470 phases of occupation in mainland East, Southeast and South Asia. The researchers modelled the likely spread of rice agriculture using an algorithm known as Fast Marching, which was used to estimate least-cost distances based on simple geographical features and suitability of regions for rice agriculture. Existing knowledge of archaeological evidence for rice was used to infer backwards towards probable areas of origin for rice cultivation. The researchers also used goodness of fit to test various previously-published hypotheses of the origin of rice agriculture against the overall archaeological rice database.

The unconstrained search for the most likely origin identified a region between the Lower and Middle Yangtze, specifically the northeast of Jiangxi Province, where there is little archaeobotanical evidence for early rice agriculture. However, the algorithm was trying to find the best-fitting single source and was unable to identify multiple origin scenarios. In such cases, it will highlight an area in between the various true origins.

The next step was to test seven previously-published hypotheses, labelled L1 to L7 in the study:
L1 Ganges, Burma and northern Vietnam
L2 Ganges, Northern Thailand and lower Yangtze
L3 Middle Yangtze and northern Bay of Bengal
L4 Pearl River delta
L5 Middle Yangtze
L6 Lower Yangtze
L7 Middle and Lower Yangtze

Of these, the last model, favouring two independent origins in the Middle and the Lower Yangtze, gave the best fit with the data and is also the most consistent with the unconstrained search. The authors of the report claim that the L7 ‘dual Yangtze’ model is so well supported over the second-best match, the L6 Lower Yangtze scenario, that the situation is compared to randomly drawing 125 million white balls out of an urn and asking whether this is sufficient evidence that the urn contains only white balls, versus containing an equal amount of white and black balls.

Whether such optimism is justified, only time and further studies will tell. However, the results agree with the conclusions of many archaeologists who have recently focused on the Middle and Lower Yangtze basin. There is currently no reason to favour either over the other as a more likely source region of rice domestication episode. Instead, multiple, distinct domestication episodes seems the most plausible hypothesis in the current state of our evidence. Cultural differences between the Neolithic traditions of the Lower and Middle Yangtze, including the earliest preserved field systems, makes it unlikely that rice agriculture diffused between the two regions.

Silva, F. et al., Modelling the Geographical Origin of Rice Cultivation in Asia Using the Rice Archaeological Database. PLoS One 10 (9), e0137024. (2015).x