Tuesday, 28 December 2010

How Neanderthals cooked their food

But the Neanderthals were also capable of harvesting and processing plant foods. In a study published in the US journal PNAS, calculus was removed from the teeth of three Neanderthal individuals: Shanidar III from Shanidar Cave, Iraq and Spy I and Spy II from Spy Cave, Belgium. Shanidar III yielded a large number starch grains, some of which were identified as originating from the Triticeae tribe of grasses, which includes the wild relatives of wheat, barley and rye. Others were from legumes. Importantly, many of the grains had been cooked. Although less numerous than the starch grains, a number of phytoliths were also recovered. These are rigid microscopic bodies, composed of silica, that occur in many plants and serve a number of purposes, including lending the plant structural rigidity and making it distasteful to predators. The bulk of the phytoliths recovered from Shanidar III originated from date palms. Starch grains were also recovered from the two Spy Cave Neanderthals. Some were found to be from tubers, possibly of water lilies. Others were from grass seeds, possibly sorghum.

Although neither site has yielded evidence of stone artefacts specialized for use as grinding implements, or of storage features, there is clear evidence that at both sites Neanderthals were employing preparation techniques which increased the edibility and nutritional quality of plant foods, including husking and cooking of seeds. Date palms have different harvest seasons to barley and legumes, suggesting that the Shanidar Neanderthals practiced seasonal rounds of collecting and scheduled returns to harvest areas.

Anthropologists have long been interested in the timing of two major hominin dietary adaptations; the cooking of plant foods and an expansion in dietary breadth or “broad spectrum revolution”. This led to the incorporation of a diversity of plant foods such as grass and other seeds that are nutritionally rich but relatively costly to exploit. That the Neanderthals mastered both adaptations in two widely-separated climates – Mediterranean and northern oceanic – is further proof of their sophistication.

Henry, A., Brooks, A., & Piperno, D. (2010). Microfossils in calculus demonstrate consumption of plants and cooked foods in Neanderthal diets (Shanidar III, Iraq; Spy I and II, Belgium). PNAS , Early Edition, 1-6.

Thursday, 23 December 2010

Modern humans interbred with Denisovans

In 2008, a distal manual phalanx of from a hominin little finger was recovered from Denisova Cave in the Altai Mountains of southern Siberia. The cave is named for a hermit called Dionisij (Denis) who is supposed to have lived there in 18th Century, but if this is true he was only the latest in a long line of inhabitants.

In April 2010, a report was published in the journal Nature (Krause, et al., 2010) suggesting that the phalanx had belonged to a hitherto-unknown human species. The small bone was dated by stratigraphic methods and found to be in the region of 30,000 to 48,000 years old. It is believed to have belonged to a child aged between 5 and 7 years old, but other than that no morphological classification could be made. However, due to the cool, dry climate, it proved to be possible to extract DNA from the bone and isolate mtDNA fragments, from which it proved possible to sequence the entire mitochondrial genome. Because we inherit our mtDNA solely from our mothers, this led to the find being dubbed X Woman, despite being from a juvenile of then unknown gender.

At the time in question, Neanderthals, identified as such by their mtDNA, were living less than 100 km (60 miles) away. The presence of an Upper Palaeolithic industry at Siberian sites such as Kara-Bom and Denisova itself has been taken as evidence for the appearance of modern humans in the Altai before 40,000 years ago. The expectation, therefore, was that the mitochondrial DNA from the bone would match that of either Neanderthals or modern humans, but neither turned out to be the case. Instead, sequencing revealed that X Woman had last shared a common ancestor with Neanderthals and modern humans about a million years ago.

X Woman clearly wasn’t a Neanderthal or a modern human, but what was she (if indeed she was a “she”)? One possibility was Homo heidelbergensis, the presumptive common ancestor of the Neanderthals and modern humans. But Homo heidelbergensis appeared no earlier than 600,000 years ago – long after X Woman’s ancestors. On the other hand, the date of one million years was too late for X Woman to be a late-surviving descendant of the first wave of Homo erectus to reach the Far East.

Towards the end of 2010, a second report was released in Nature detailing the sequencing of X Woman’s nuclear genome (Reich, et al., 2010). It turned out that “X-Woman” lacked a Y-chromosome and therefore was indeed female. Also described in the same report was an upper molar tooth. The latter appeared to be from a young adult and also yielded mtDNA, which in turn confirmed that it belonged to a different individual to phalanx. For this reason, the term “X-Woman” was dropped in favour of “Denisovan”.

According to the report, both mitochondrial and nuclear genomes suggest that the Denisovans are more closely related to Neanderthals than they are to modern humans. The nuclear data suggested that the Denisovans diverged from Neanderthals 640,000 years ago and from present-day Africans 804,000 years ago, suggesting that Densovans and Neanderthals were sister groups, sharing a more recent common ancestor than modern humans and Neanderthals. Africans were used for the comparison to avoid the confounding effects of the interbreeding thought to have occurred between archaic humans (previously thought to be Neanderthals) and the first modern humans to leave Africa. It was also found that the archaic component of the modern Eurasian genome has closer affinities to Neanderthals than to Denisovans, confirming that the interbreeding did occur with the former rather than the latter.

The divergence data obtained from the nuclear DNA is rather at odds with that obtained from the mtDNA. The report suggested two possible causes; firstly interbreeding between Denisovans and as yet unknown hominins; secondly, that the Denisovans retained an archaic mitochondrial lineage that has been lost from Neanderthals and modern humans due to the effects of genetic drift. The latter explanation is the more parsimonious, but the report concluded that the two scenarios were equally likely according to the data.

The most remarkable finding was that 4.8 percent of the nuclear genome of present-day Papuans derives from Denisovans, greater than the Neanderthal contribution of 2.5 percent and meaning that uniquely for modern humans, the Papuans are more closely-related to Denisovans than they are to Neanderthals. Overall, the data was consistent with a scenario in which modern humans, on leaving Africa, interbred with Neanderthals and then, at some subsequent point, the ancestors of present-day Papuans interbred with Denisovans, but this did not affect any other non-African populations. The implication is that Denisovans were present in Southeast Asia as well as southern Siberia. This in turn raises the possibility that the archaic humans living in the Far East as recently as 27,000 years ago (Swisher, et al., 1996), conventionally described as late Homo erectus, may in fact be Denisovans.

The Denisova tooth, which is probably a third or possibly second left upper molar, is fairly large, within the size range occupied by Homo erectus and Homo habilis and larger than that typical of Neanderthals and early modern humans. But the report failed to note that some early modern human teeth are also very large, such as those associated with the 35,000 year old lower jawbone from Peştera cu Oase in Romania I) (Trinkaus, Milota, Rodrigo, Mircea, & Moldovan, 2003; Trinkaus, et al., 2003). Size alone probably does not tell us very much. That the tooth shares no derived morphological features with Neanderthals or modern humans further indicates the distinctiveness of the Denisovans; but it also lacks any features in common with the very few third upper molars that have been recovered from other late archaic hominins in the Far East. Thus the tooth fails to support a connection between the Denisovans and known archaic human fossil remains from the Far East.

Clearly there is a very interesting story here, but until further fossil and/or genetic evidence comes to light, there is nothing more definite that can be said at this stage.

Krause, J., Fu, Q., Good, J., Viola, B., Shunkov, M., Derevianko, A., et al. (2010). The complete mitochondrial DNA genome of an unknown hominin from southern Siberia. Nature , 464, 894-897.

Reich, D., Green, R., Kircher, M., Krause, J., Patterson, N., Durand, E., et al. (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia. Nature , 468, 1053-1060.

Swisher, C., Rink, W., Anton, S., Schwarcz, H., Curtis, G., Suprijo, A., et al. (1996). Latest Homo erectus of Java: Potential Contemporaneity with Homo sapiens in Southeast Asia . Science , 274, 1870 - 1874.

Trinkaus, E., Milota, S., Rodrigo, R., Mircea, G., & Moldovan, O. (2003). Early modern human cranial remains from the Pestera cu Oase, Romania. Journal of Human Evolution , 45, 245–253.

Trinkaus, E., Moldovan, O., Milota, Ş., Bîlgăr, A., Sarcina, L., Athreya, S., et al. (2003). An early modern human from Peştera cu Oase, Romania. PNAS , 100 (20), 11231–11236.

© Christopher Seddon 2010

Wednesday, 22 December 2010

Grim fate of Neanderthal family group, 49,000 years ago

Evidence has come to light of the grim fate of a Neanderthal family group that lived in Spain 49,000 years ago. After apparently enduring a lifetime of privation, they were killed and eaten by members of a neighbouring Neanderthal group – presumably themselves on the brink of starvation and thus driven to extremities.

In 1994, extensive human remains were found at El Sidrón, an extensive system of karstic limestone caves in the Asturias region of northern Spain. Systematic excavation commenced in 2000 and to date around 1800 hominin skeletal fragments and 400 Mousterian-type stone tools have been recovered. The latter include side scrapers, denticulate pieces, a hand axe, and several Levallois points. The human remains are thought to represent twelve Neanderthal individuals, including three adult males, three adult females, three male adolescents and two juveniles and an infant of unknown gender.

A group size of 12 individuals at El Sidron is reasonably consistent with a previous estimate of between 8 to 10 individuals per Neanderthal group, based on the size of sleeping and combustion activity areas in the long-occupied rock shelter of Abric Romaní, near Barcelona. However, because the original external deposit cannot be studied, it could not be rules out that the El Sidrón group was larger and that some original members are not represented among the remains.

The tools and remains were found in a side gallery deep within the cave complex, and was probably introduced into the cave from the surface when a violent storm caused an upper gallery or a series of fissures to collapse. Pebbles and clay were also dragged down from the surface. The whole assemblage is around 49,000 years old. Around 18 percent of the tools have been refitted, suggesting that they are all the same age and that the associated human remains represent all or part of a contemporaneous social group of Neanderthals, who died at around the same time.

The low temperature of the side gallery meant that genetic material has survived and mitochondrial DNA has been extracted from each of the individuals. It was found that all three of the adult males carried the same mitochondrial lineage, but the three adult females all carried different lineages. Mitochondrial DNA is not a part of the primary genome and is inherited solely from the maternal line. The implication, therefore, is that the males shared the same maternal lineages but the females all had different maternal lineages. This suggests that in Neanderthal groups, mature males remained within their family birth group, but females came from outside. Patrilocality, as it is known, is present in about 70 percent of modern human societies, where men remaining in the family home but women move to the home of their new husband upon marriage.

But there is a darker side to the discoveries. All the El Sidrón individuals suffered from developmental stress, or periods of growth arrest, presumably arising from malnutrition. This is indicated by deficiencies in dental enamel, present on over 50 percent of the group members’ incisors, canines and premolars and over 30 percent of their molars. Five of the members had experienced two such episodes of growth arrest and one adult had experienced four. It is clear that for this extended Neanderthal family, life was very difficult – and in the end, it seems, they met a grim fate.

Cut marks and breaks have been found on many of the bones, including lower jawbones, skulls and long bones; evidence of skinning activity and extraction of bone marrow and brains – in other words, cannibalism.

Lalueza-Foxa, C., Rosas, A., Estalrrich, A., Gigli, E., Campos, P., García-Tabernero, A., et al. (2010, December). Genetic evidence for patrilocal mating behavior among Neandertal groups. PNAS .

Rosas, A., Martınez-Maza, C., Bastira, M., Garcıa-Tabernero, A., Lalueza-Fox, C., Huguet, R., et al. (2006). Paleobiology and comparative morphology of a late Neandertal sample from El Sidron, Asturias, Spain. PNAS , 103 (51), 19266–19271.

Vallverdu, J., Vaquero, M., Caceres, I., Allue, E., Rosell, J., Saladie, P., et al. (2010). Sleeping Activity Area within the Site Structure of Archaic Human Groups Evidence from Abric Romanı Level N Combustion Activity Areas. Current Anthropology , 51 (1), 137-145.

© Christopher Seddon 2010