Neanderthal extinction

Neanderthal extinction began around 40,000 years ago in Europe, after anatomically modern humans had reached the continent. This date, which is based on research published in Nature in 2014, is much earlier than previous estimates, and it was established through improved radio carbon dating methods analyzing 40 sites from Spain to Russia. The survey did not include sites in Asia, where Neanderthals may have survived longer.[1]

Hypotheses on the fate of the Neanderthals include violence from encroaching anatomically modern humans,[2] parasites and pathogens, competitive replacement, competitive exclusion, extinction by interbreeding with early modern human populations,[3] and failure or inability to adapt to climate change. It is unlikely that any one of these hypotheses is sufficient on its own; rather, multiple factors probably contributed to the demise of an already widely-dispersed population.[4][5]

Coexistence prior to extinction

Neanderthal tools
modern human tools

In research published in Nature in 2014, an analysis of radiocarbon dates from forty Neanderthal sites from Spain to Russia found that the Neanderthals disappeared in Europe between 41,000 and 39,000 years ago with 95% probability. The study also found with the same probability that modern humans and Neanderthals overlapped in Europe for between 2,600 and 5,400 years.[1] Modern humans reached Europe between 45,000 and 43,000 years ago.[6] Most recent numbers based on improved radiocarbon dating indicate that Neanderthals disappeared around 40,000 years ago, which overturns older carbon dating which indicated that Neanderthals may have lived as recently as 24,000 years ago,[7] including in refugia on the south coast of the Iberian peninsula such as Gorham's Cave.[8][9] Inter-stratification of Neanderthal and modern human remains has been suggested,[10] but is disputed.[11]

Possible cause of extinction

Violence

Some authors have discussed the possibility that Neanderthal extinction was either precipitated or hastened by violent conflict with Homo sapiens. Conflict and warfare are virtually ubiquitous features of hunter-gatherer societies, including conflicts over limited resources, such as prey and water.[12] It is therefore plausible to suggest that violence, including primitive warfare, would have transpired between the two human species.[13] The hypothesis that early humans violently replaced Neanderthals was first proposed by French palaeontologist Marcellin Boule (the first person to publish an analysis of a Neanderthal) in 1912.[14] Several finds in both Homo-sapiens and Neanderthal bones indicate inter-species aggression from injuries (grooves in the bones themselves) that could only have come from spear or other projectile tips crafted with prevalent tool-making methods contemporary to the time.[15]

Parasites and pathogens

Another possibility is the spread among the Neanderthal population of pathogens or parasites carried by Homo sapiens.[16] Neanderthals would have limited immunity to diseases they had not been exposed to, so diseases carried into Europe by Homo sapiens could have been particularly lethal to them if Homo sapiens were relatively resistant. If it were relatively easy for pathogens to leap between these two similar species, perhaps because they lived in close proximity, then Homo sapiens would have provided a pool of individuals capable of infecting Neanderthals and potentially preventing the epidemic from burning itself out as Neanderthal population fell. On the other hand, the same mechanism could work in reverse, and the resistance of Homo sapiens to Neanderthal pathogens and parasites would need explanation. An examination of human and Neanderthal genomes and adaptations regarding pathogens or parasites may shed light on this issue.

Competitive replacement

Sapiens and Neanderthal skulls

Species specific disadvantages

Slight competitive advantage on the part of modern humans has accounted for Neanderthals' decline on a timescale of thousands of years.[17]

Generally small and widely-dispersed fossil sites suggest that Neanderthals lived in less numerous and socially more isolated groups than contemporary Homo sapiens. Tools such as Mousterian flint stone flakes and Levallois points are remarkably sophisticated from the outset, yet they have a slow rate of variability and general technological inertia is noticeable during the entire fossil period. Artifacts are of utilitarian nature, and symbolic behavioral traits are undocumented before the arrival of modern humans in Europe around 40,000 to 35,000 years ago.[18][19]

Jared Diamond, supporter of competitive replacement, points out in his book The Third Chimpanzee that the genocidal replacement of Neanderthals by modern humans is comparable to patterns of behavior that occur whenever people with advanced technology clash with less advanced people.[20]

Division of labor

In 2006, two anthropologists of the University of Arizona proposed an efficiency explanation for the demise of the Neanderthals.[21] In an article titled "What's a Mother to Do? The Division of Labor among Neanderthals and Modern Humans in Eurasia",[22] it was posited that Neanderthal division of labor between the sexes was less developed than Middle paleolithic Homo sapiens. Both male and female Neanderthals participated in the single occupation of hunting big game, such as bison, deer, gazelles and wild horses. This hypothesis proposes that the Neanderthal's relative lack of labor division resulted in less efficient extraction of resources from the environment as compared to Homo sapiens.

Anatomical differences and running ability

Researchers such as Karen L. Steudel of the University of Wisconsin have highlighted the relationship of Neanderthal anatomy (shorter and stockier than that of modern humans) and the ability to run and the requirement of energy (30% more).[23]

Nevertheless, in the recent study, researchers Martin Hora and Vladimir Sladek of Charles University in Prague show that Neanderthal lower limb configuration, particularly the combination of robust knees, long heels and short lower limbs, increased the effective mechanical advantage of Neanderthal knee and ankle extensors, thus reducing the force needed and the energy spent for locomotion significantly. The walking cost of the Neanderthal male is now estimated to be 8–12% higher than that of anatomically modern males, whereas the walking cost of the Neanderthal female is considered to be virtually equal to that of anatomically modern females.[24]

Other researchers, like Yoel Rak, from Tel-Aviv University in Israel, have noted that the fossil records show that Neanderthal pelvises in comparison to modern human pelvises would have made it much harder for Neanderthals to absorb shock and to bounce off from one step to the next, giving modern humans another advantage over Neanderthals in running and walking ability.[25]

Modern humans' advantage in hunting warm climate animals

Pat Shipman, from Pennsylvania State University in the United States, argues that the domestication of the dog gave modern humans an advantage when hunting.[26] The oldest remains of domesticated dogs were found in Belgium (31,700 BP) and in Siberia (33,000 BP).[27][28] A survey of early sites of modern humans and Neanderthals with faunal remains across Spain, Portugal and France provided an overview of what modern humans and Neanderthals ate.[29] Rabbit became more frequent, while large mammals – mainly eaten by the Neanderthals – became increasingly rare. In 2013, DNA testing on the "Altai dog", a paleolithic dog's remains from the Razboinichya Cave (Altai Mountains), has linked this 33,000-year-old dog with the present lineage of Canis lupus familiaris.[30]

Interbreeding

Human-Neandertal mtDNA
Neanderthal DNA extraction

Interbreeding can only account for a certain degree of Neanderthal population decrease. A homogeneous absorption of an entire species is a rather unrealistic idea. This would also be counter to strict versions of the Recent African Origin, since it would imply that at least part of the genome of Europeans would descend from Neanderthals, who left Africa at least 350,000 years ago.

The most vocal proponent of the hybridization hypothesis is Erik Trinkaus of Washington University.[31][32] Trinkaus claims various fossils as hybrid individuals, including the "child of Lagar Velho", a skeleton found at Lagar Velho in Portugal.[33] In a 2006 publication co-authored by Trinkaus, the fossils found in 1952 in the cave of Peștera Muierilor, Romania, are likewise claimed as hybrids.[34]

Genetic studies indicate some form of hybridization between archaic humans and modern humans had taken place after modern humans emerged from Africa. An estimated 1–4% of the DNA in Europeans and Asians (e.g. French, Chinese and Papua probands) is non-modern, and shared with ancient Neanderthal DNA rather than with sub-Saharan Africans (e.g. Yoruba and San probands).[35]

Modern-human findings in Abrigo do Lagar Velho, Portugal allegedly featuring Neanderthal admixtures have been published.[36] However, the interpretation of the Portuguese specimen is disputed.[37]

Jordan, in his work Neanderthal, points out that without some interbreeding, certain features on some "modern" skulls of Eastern European Cro-Magnon heritage are hard to explain. In another study, researchers have recently found in Peştera Muierilor, Romania, remains of European humans from ~37,000–42,000 years ago[38]who possessed mostly diagnostic "modern" anatomical features, but also had distinct Neanderthal features not present in ancestral modern humans in Africa, including a large bulge at the back of the skull, a more prominent projection around the elbow joint, and a narrow socket at the shoulder joint. Analysis of one skeleton's shoulder showed these humans, like Neanderthals, did not have the full capability for throwing spears.[39]

The Neanderthal genome project published papers in 2010 and 2014 stating that Neanderthals contributed to the DNA of modern humans, including most humans outside sub-Saharan Africa, as well as a few populations in sub-Saharan Africa, through interbreeding, likely between 50,000 and 60,000 years ago.[40][41][42] Recent studies also show that a few Neanderthals began mating with ancestors of modern humans long before the large "out of Africa migration" of the present day non-Africans, as early as 100,000 years ago.[43] In 2016, research indicated that there were three distinct episodes of interbreeding between modern humans and Neanderthals: the first encounter involved the ancestors of non-African modern humans, probably soon after leaving Africa; the second, after the ancestral Melanesian group had branched off (and subsequently had a unique episode of interbreeding with Denisovans); and the third, involving the ancestors of East Asians only.[44]

While interbreeding is viewed as the most parsimonious interpretation of the genetic discoveries, the authors point out they cannot conclusively rule out an alternative scenario, in which the source population of non-African modern humans was already more closely related to Neanderthals than other Africans were, due to ancient genetic divisions within Africa.

Among the genes shown to differ between present-day humans and Neanderthals were RPTN, SPAG17, CAN15, TTF1 and PCD16.

Neanderthal DNA Comparison (SharedDNA)

Climate change

Snowbound, painting of Neanderthals in a blizzard, Charles R. Knight, 1911

Neanderthals went through a demographic crisis in Western Europe that seems to coincide with climate change that resulted in a period of extreme cold in Western Europe. "The fact that Neanderthals in Western Europe were nearly extinct, but then recovered long before they came into contact with modern humans came as a complete surprise to us," said Love Dalén, associate professor at the Swedish Museum of Natural History in Stockholm. If so, this would indicate that Neanderthals may have been very sensitive to climate change.[45]

Natural catastrophe

A number of researchers have argued that the Campanian Ignimbrite Eruption, a volcanic eruption near Naples, Italy, about 39,280 ± 110 years ago (older estimate ~37,000 years), erupting about 200 km3 (48 cu mi) of magma (500 km3 (120 cu mi) bulk volume) has contributed to the extinction of Neanderthal man.[46] The argument has been developed by Golovanova et al.[47][48]

Although Neanderthals had encountered several Interglacials during 250,000 years in Europe[49] inability to adapt their hunting methods caused their extinction facing H. sapiens competition when Europe changed into a sparsely vegetated steppe and semi-desert during the last Ice Age.[50] Studies of sediment layers at Mezmaiskaya Cave suggest a severe reduction of plant pollen.[48] The damage to plant life would have led to a corresponding decline in plant-eating mammals hunted by the Neanderthals.[48][51][52]

See also

References

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  2. ↑ Hortolà P, Martínez-Navarro B (2013). "The Quaternary megafaunal extinction and the fate of Neanderthals: An integrative working hypothesis". Quaternary International. 295: 69–72. Bibcode:2013QuInt.295...69H. doi:10.1016/j.quaint.2012.02.037.
  3. ↑ Interbreeding took place in western Asia between about 65,000 and 47,000 years ago, see Kuhlwilm, M.; Gronau, I.; Hubisz, M.J.; de Filippo, C.; Prado-Martinez, J.; Kircher, M.; et al. (2016). "Ancient gene flow from early modern humans into Eastern Neanderthals". Nature. 530 (7591): 429–433. Bibcode:2016Natur.530..429K. doi:10.1038/nature16544. PMC 4933530. PMID 26886800.
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  5. ↑ "Did a Volcanic Eruption Kill Off the Neandertals?". Science for writers. March 25, 2015. Retrieved September 20, 2016.
  6. ↑ John Noble Wilford (2011-11-02). "Fossil Teeth Put Humans in Europe Earlier Than Thought". Nytimes.com. Retrieved 2017-02-23.
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  8. ↑ Rincon, Paul (13 September 2006). "Neanderthals' 'last rock refuge'". BBC News. Retrieved 11 October 2009.
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  32. ↑ Modern Humans, Neanderthals May Have Interbred; Humans and Neanderthals interbred Archived 2009-02-22 at the Wayback Machine.
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  40. ↑ Sánchez-Quinto, F; Botigué, LR; Civit, S; Arenas, C; Avila-Arcos, MC; Bustamante, CD; Comas, D; Lalueza-Fox, C (October 17, 2012). "North African Populations Carry the Signature of Admixture with Neandertals". PLoS ONE. 7 (10): e47765. Bibcode:2012PLoSO...747765S. doi:10.1371/journal.pone.0047765. PMC 3474783. PMID 23082212.
  41. ↑ Fu, Q; Li, H; Moorjani, P; Jay, F; Slepchenko, S. M.; Bondarev, A. A.; Johnson, P. L.; Aximu-Petri, A; Prüfer, K; De Filippo, C; Meyer, M; Zwyns, N; Salazar-García, D. C.; Kuzmin, Y. V.; Keates, S. G.; Kosintsev, P. A.; Razhev, D. I.; Richards, M. P.; Peristov, N. V.; Lachmann, M; Douka, K; Higham, T. F.; Slatkin, M; Hublin, J. J.; Reich, D; Kelso, J; Viola, T. B.; Pääbo, S (23 October 2014). "Genome sequence of a 45,000-year-old modern human from western Siberia". Nature. 514 (7523): 445–449. Bibcode:2014Natur.514..445F. doi:10.1038/nature13810. hdl:10550/42071. PMC 4753769. PMID 25341783.
  42. ↑ Brahic, Catherine. "Humanity's forgotten return to Africa revealed in DNA", The New Scientist (February 3, 2014).
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  44. ↑ "The Combined Landscape of Denisovan and Neanderthal Ancestry in Present-Day Humans", Current Biology, Sankararaman et al., 26, 1241–1247, 2016
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  48. 1 2 3 Than, Ker (September 22, 2010). "Volcanoes Killed Off Neanderthals, Study Suggests". National Geographic. Retrieved 23 September 2010.
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  50. ↑ Climate Change Killed Neandertals, Study Says, National Geographic News
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