Neanderthal extinction hypotheses

Neanderthal extinction hypotheses are theories about how Neanderthals became extinct around 30,000 years ago.^[1] Since their discovery, both the Neanderthals' place in the human family tree and their relation to modern Europeans has been hotly debated. At different times they have been classified as a separate species (Homo neanderthalensis) and as a subspecies of Homo sapiens (Homo sapiens neanderthalensis).

Theories on the fate of the Neanderthals include an inability to cope with climate change, competitive exclusion or even genocide by anatomically modern humans, and hybridization, effectively being absorbed into the Cro-Magnon population.

Coexistence prior to extinction

Neanderthals and modern humans coexisted in Europe for several thousand years, but the duration of this period is uncertain.^[2] Modern humans may have first migrated to Europe 40–43,000 years ago,^[3] and Neanderthals may have lived as recently as 24,000 years ago in refugia on the south coast of the Iberian peninsula such as Gorham's Cave.^[4][5] Inter-stratification of Neanderthal and modern human remains has been suggested,^[6] but is disputed.^[7]

Rapid extinction by violence

Jared Diamond has suggested a scenario of violent conflict comparable to the genocides suffered by indigenous peoples in recent human history.^[8]

Rapid extinction by parasites and pathogens

Another possibility raised by Diamond and others, paralleling colonialist history, would be a greater susceptibility on the part of the Neanderthals to pathogens introduced by Cro-Magnon man. Diamond argues that asymmetry in susceptibility to pathogens is a consequence of the difference in lifestyle.^{[citation needed]}. A pandemic will generally have a limited mortality because the pathogen needs a host in order to spread. If two species are similar and lives side by side, then the survival of one species becomes less important for the pathogen. And in the end it may be three outcomes: divergence, exchange of genes, downfall. A disease that should be mentioned is gonorrhea. It arose about 200,000 years ago. Along with differences in social and sexual behavior, this sexually transmitted infection could be the cause of the extinction.

Competitive replacement

Even a slight competitive advantage on the part of modern humans could account for Neanderthals' replacement by anatomically modern humans on a timescale of 10,000–20,000 years.^[3]

The theory 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.^[9]

Another supporter of competitive replacement is Jared Diamond who points out in his book The Third Chimpanzee that the genocidal replacement of Neanderthals by modern humans is similar to modern human patterns of behavior that occur whenever people with advanced technology invade the territory of less advanced people.^[10]

Division of labor

In 2006, two anthropologists of the University of Arizona proposed a new explanation for the demise of the Neanderthals.^[11] In an article titled "What's a Mother to Do? The Division of Labor among Neanderthals and Modern Humans in Eurasia",^[12] they theorize that Neanderthals like Middle paleolithic Homo sapiens did not have a division of labor between the sexes. Under this hypothesis, both male and female Neanderthals participated in the single main occupation of hunting big game that flourished in Europe in the ice age like bison, deer, gazelles and wild horses.

This theory is in contrast to humans who were better able to use the resources of the environment because of a division of labor, with the women hunting small game and gathering plant foods. In addition, because big game hunting was so dangerous, this made humans, at least males, more resilient.

Anatomical differences and running ability

Researchers including Karen L. Steudel of the University of Wisconsin have proposed that because Neanderthals had limbs that were shorter and stockier than those of modern humans, and because of other anatomical differences in their limbs, the primary reason the Neanderthals were not able to survive is related to the fact that they could not run as fast as modern humans, and they would require 30% more energy than modern humans would for running or walking.^{[13][not in citation given]}

This would have given modern humans a huge advantage in battle. 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.^[14]

Interbreeding

Main article: Neanderthal admixture

Further information: Neanderthal Genome Project

An alternative to extinction is that Neanderthals were absorbed into the Cro-Magnon population by interbreeding. This would 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.^[15] Trinkaus claims various fossils as hybrid individuals, including the "child of Lagar Velho", a skeleton found at Lagar Velho in Portugal dated to about 24,000 years ago.^[16] In a 2006 publication co-authored by Trinkaus, the fossils found in 1952 in the cave of Pestera Muierii, Romania, are likewise claimed as hybrids.^[17]

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 to 4 percent of the DNA in Europeans and Asians (i.e. French, Chinese and Papua probands) is non-modern, and shared with ancient Neanderthal DNA rather than with sub-Saharan Africans (i.e. Yoruba and San probands).^[18]

Modern-human findings in Abrigo do Lagar Velho, Portugal of 24,500 years ago, allegedly featuring Neanderthal admixtures, have been published.^[19] However, the interpretation of the Portuguese specimen is disputed.^[20]

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 30 thousand years ago 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 Neanderthal, did not have the full capability for throwing spears.^[21]

An analysis of a first draft of the Neanderthal genome by Richard E. Green et al. from Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany released in May 2010 indicates interbreeding may have occurred.^[22][23] "Those of us who live outside Africa carry a little Neanderthal DNA in us," said Pääbo, who led the study. "The proportion of Neanderthal-inherited genetic material is about 1 to 4 percent. It is a small but very real proportion of ancestry in non-Africans today," says Dr. David Reich of Harvard Medical School in Boston, who worked on the study. This research compared the genome of the Neanderthals to five modern humans from China, France, sub-Saharan Africa, and Papua New Guinea. The finding is that about 1 to 4 percent of the genes of the non-Africans came from Neanderthals, compared to the baseline defined by the two Africans. This indicates a gene flow from Neanderthals to modern humans, i.e., interbreeding between the two populations. Since the three non-African genomes show a similar proportion of Neanderthal sequences, the interbreeding must have occurred early in the migration of modern humans out of Africa, perhaps in the Middle East. No evidence for gene flow in the direction from modern humans to Neanderthals was found. The latter result would not be unexpected if contact occurred between a small colonizing population of modern humans and a much larger resident population of Neanderthals. A very limited amount of interbreeding could explain the findings, if it occurred early enough in the colonization process.^[22]

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.^[22]

Among the genes shown to differ between present-day humans and Neanderthals were RPTN, SPAG17, CAN15, TTF1 and PCD16.^[22]

Climate change

Another hypothesis involves climate change. Although it is believed that Neanderthals had clothing,^[24] it has been proposed that failure to adapt their hunting methods caused their extinction when Europe changed into a sparsely vegetated steppe and semi-desert during the last Ice Age.^[25] Requiring more energy to move and hunt than their early modern human counterparts, Neanderthals would have been more susceptible to less food being available as a result of climate change.^{[citation needed]} A string of major volcanic eruptions 40,000 years BP, affecting the region between Italy and the Caucasus Mountains, may have contributed to the Neanderthals' decline by reducing their food supply.^[26] Studies of sediment layers at Mezmaiskaya Cave suggest a severe reduction of plant pollen.^[26] The damage to plant life would have led to a corresponding decline in plant-eating mammals hunted by the Neanderthals.^[26][27]

See also

• List of hominina (hominid) fossils (with images)
• Neanderthals in popular culture
• Quaternary extinction event

References

1. ^ Last Neanderthals Were Smart, Discovery Channel
2. ^ Mellars P (February 2006). "A new radiocarbon revolution and the dispersal of modern humans in Eurasia". Nature 439 (7079): 931–935. Bibcode 2006Natur.439..931M. doi:10.1038/nature04521. PMID 16495989. 
3. ^ ^{a b} Banks, William E.; Francesco d'Errico, A. Townsend Peterson, Masa Kageyama, Adriana Sima, Maria-Fernanda Sánchez-Goñi (24 December 2008). Harpending, Henry. ed. "Neanderthal Extinction by Competitive Exclusion". PLoS ONE (Public Library of Science) 3 (12): e3972. Bibcode 2008PLoSO...3.3972B. doi:10.1371/journal.pone.0003972. ISSN 1932-6203. PMC 2600607. PMID 19107186. http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0003972. 
4. ^ Rincon, Paul (13 September 2006). "Neanderthals' 'last rock refuge'". BBC News. http://news.bbc.co.uk/1/hi/5343266.stm?lsm. Retrieved 2009-10-11. 
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7. ^ Zilhão, João; Francesco d’Errico, Jean-Guillaume Bordes, Arnaud Lenoble, Jean-Pierre Texier, and Jean-Philippe Rigaud (2006). "Analysis of Aurignacian interstratification at the Châtelperronian-type site and implications for the behavioral modernity of Neandertals". PNAS 103 (33): 12643–12648. Bibcode 2006PNAS..10312643Z. doi:10.1073/pnas.0605128103. PMC 1567932. PMID 16894152. http://www.pnas.org/content/103/33/12643.full. 
8. ^ Diamond, Jared (1992). The Third Chimpanzee: The Evolution and Future of the Human Animal. Harper Perennial. ISBN 0-06-098403-1. 
9. ^ Boule, M 1912, Les hommes fossiles, Masson, Paris.
10. ^ Diamond, J 1992, The Third Chimpanzee: The Evolution and Future of the Human Animal, Harper Collins, New York, p 45.
11. ^ Nicholas Wade, "Neanderthal Women Joined Men in the Hunt", from The New York Times, December 5, 2006
12. ^ Steven L. Kuhn and Mary C. Stiner, "What's a Mother to Do? The Division of Labor among Neandertals and Modern Humans in Eurasia", Current Anthropology, Volume 47, Number 6, December 2006 doi:10.1086/507197
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15. ^ Dan Jones: The Neanderthal within., New Scientist 193.2007, H. 2593 (3 March), 28–32. Modern Humans, Neanderthals May Have Interbred; Humans and Neanderthals interbred
16. ^ "The Lagar Velho 1 Skeleton". TalkOrigins. 2000. http://www.talkorigins.org/faqs/homs/lagarvelho.html. Retrieved January 2011. ; Sample, Ian (14 September 2006). "Life on the edge: was a Gibraltar cave last outpost of the lost neanderthal?". The Guardian. http://www.guardian.co.uk/science/story/0,,1871842,00.html. Retrieved January 2011. ; "Not a lasting last for the Neandertals". John Hawks Weblog. September 2006. http://johnhawks.net/weblog/reviews/neandertals/gorhams_28000_date_2006.html. Retrieved January 2011. 
17. ^ Soficaru A, Dobos A, Trinkaus E (November 2006). "Early modern humans from the Pestera Muierii, Baia de Fier, Romania". Proc. Natl. Acad. Sci. U.S.A. 103 (46): 17196–17201. Bibcode 2006PNAS..10317196S. doi:10.1073/pnas.0608443103. PMC 1859909. PMID 17085588. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1859909. 
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19. ^ Duarte C, Maurício J, Pettitt PB, Souto P, Trinkaus E, van der Plicht H, Zilhão J (June 1999). "The early Upper Paleolithic human skeleton from the Abrigo do Lagar Velho (Portugal) and modern-human emergence in Iberia". Proceedings of the National Academy of Sciences 96 (13): 7604–7609. Bibcode 1999PNAS...96.7604D. doi:10.1073/pnas.96.13.7604. PMC 22133. PMID 10377462. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=10377462. Retrieved 17 May 2009. 
20. ^ Ruzicka J, Hansen EH, Ghose AK, Mottola HA (February 1979). "Enzymatic determination of urea in serum based on pH measurement with the flow injection method". Analytical Chemistry 51 (2): 199–203. doi:10.1021/ac50038a011. PMID 33580. 
21. ^ Hayes, Jacqui (2 November 2006). "Humans and Neanderthals interbred". Cosmos. http://www.cosmosmagazine.com/node/814. Retrieved 17 May 2009. 
22. ^ ^{a b c d} Richard E. Green et al (2010). "A Draft Sequence of the Neanderthal Genome". Science 328 (5979): 710–722. Bibcode 2010Sci...328..710G. doi:10.1126/science.1188021. PMID 20448178. 
23. ^ Rincon, Paul (2010-05-06). "Neanderthal genes 'survive in us'". BBC News (BBC). http://news.bbc.co.uk/2/hi/science/nature/8660940.stm. Retrieved 2010-05-07. 
24. ^ Gilligan, I: "Neanderthal extinction and modern human behaviour: the role of climate change and clothing", World Archaeology, Vol. 39, No. 4. (2007), pp. 499–514.
25. ^ Climate Change Killed Neandertals, Study Says, National Geographic News
26. ^ ^{a b c} Than, Ker (September 22, 2010). "Volcanoes Killed Off Neanderthals, Study Suggests". National Geographic. http://news.nationalgeographic.com/news/2010/01/100922-volcanoes-eruptions-neanderthals-science-volcanic-humans/. Retrieved September 23, 2010. 
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External links

• Hey Good Lookin': Early Humans Dug Neanderthals – audio report by NPR