Neanderthal interaction with Cro-Magnons
Around 45,000 years ago, the Neanderthals began to be displaced by, or assimilated with, modern humans (Homo sapiens), as the Cro-Magnon people appeared in Europe. Despite this, regional pockets of Neanderthals held on for thousands of years in such areas as modern-day Croatia and the Iberian and Crimean peninsulas.
There is considerable debate about whether Cro-Magnon people accelerated the demise of the Neanderthals. Timing suggests a causal relation between the appearance of Homo sapiens in Europe and the decline of Homo neanderthalensis. Both the Neanderthals' place in the human family tree and their relation to modern Europeans have been hotly debated ever since their discovery. They have been classified as a separate species (Homo neanderthalensis) and as a subspecies of Homo sapiens (Homo sapiens neanderthalensis) at different times. The consensus has been, based on ongoing DNA research, that they were a separate branch of the genus Homo, and that modern humans are not directly descended from them (fitting with the single-origin hypothesis).
In some areas of the Middle East and the Iberian peninsula, Neanderthals did, in fact, co-exist side by side with populations of anatomically modern Homo sapiens for roughly 15,000 -20,000 years. There is also evidence that it is in these areas where the last of the Neanderthals died out and that during this period the last remnants of this species had begun to adopt — or perhaps independently innovate — some aspects of the Châtelperronian (Upper Paleolithic) tool case, which is usually exclusively associated with anatomically modern Homo sapiens.
Another possibility, paralleling colonialist history, would be a greater susceptibility to pathogens introduced by Cro-Magnon man on the part of the Neanderthals. Although Diamond and others have specifically mentioned Cro-Magnon diseases as a threat to Neanderthals, this aspect of the analogy with the contacts between colonisers and indigenous peoples in recent history can be misleading. The distinction arises because Cro-Magnons and Neanderthals are both believed to have lived a nomadic lifestyle, whereas in those genocides of the colonial era in which differential disease susceptibility was most significant, it resulted from the contact between colonists with a long history of agriculture and nomadic hunter-gatherer peoples. Diamond argues that asymmetry in susceptibility to pathogens is a consequence of the difference in lifestyle, which makes it irrelevant in the context of the analogy in which he invokes it.
On the other hand, many Native Americans before contact with Europeans were not nomadic, but agriculturalists (Mayans, Iroquois, Cherokee), and this still did not protect them from the disease epidemics brought by Europeans (Smallpox). One theory is that because they usually lacked large domesticated animal agriculture, such as cows or pigs in close contact with people (Zoonosis), they did not develop resistance to species-jumping diseases like Europeans had. (See also Guns, Germs, and Steel.) Furthermore, the nomadic Eurasian populations such as the Mongols did not get wiped out by the diseases of the agriculturalist societies they invaded and took over, like China and eastern Europe.
However, these scenarios may be more drastic than is required to explain a decline of Neanderthal population over the course of some 10,000-20,000 years: even a slight selective advantage on the part of modern humans could account for Neanderthals' replacement on such a timescale. Gradual climatic change as a cause of extinction is also a common hypothesis. Speech-related theories have been largely discredited.
The problem with a gradual extinction scenario lies in the resolution of dating methods. There have been claims for young Neanderthal sites, younger than 30,000 years old. Even claims for interstratification of Neanderthal and Modern human remains have been advanced So the fact that Neanderthals and modern humans coexisted at least for some time seems certain. However, because of difficulties in calibrating the C14 dates the duration of this period is uncertain
One skeleton that has led some researchers to claim that it shared Neanderthal and Cro-magnon features has been found at Lagar Velho in Portugal; it is uncertain whether this is in fact a hybrid of the two species, or simply an extreme individual of one or the other. This may suggest the two species may have interbred. The child skeleton does seem to be more robust than what we would expect for modern humans. However, most researchers think that it represents extreme variation within modern humans. Moreover, the skeleton is dated to about 24,000 years BP. Until recently, this implied that a hybrid population survived in the region for thousands of years. However, a Neanderthal population in Gibraltar dated to about the same time has recently been found. The dating evidence for this claim is debated, though. Claims for Neanderthal sites that were advanced in the past have in the end all been revised to pre-30 kyr. It has also been speculated that these hybrid individuals could have been sterile.
It is very difficult to prove as the genetic differences between Neanderthals and Cro-magnons were far more minute than the morphological differences between the two species might seem to indicate. Tests comparing Neanderthal and modern human mitochondrial DNA show some dissimilarity. The mtDNA indicated a split between Homo sapiens and Neanderthals occurred little more than 500,000 years ago. This can be compared with the 1 million years split between various canine species, which still can interbreed. Morphological symmetry and asymmetry often belies genetic truth in the case of these ancient Homo populations. It is possible that the Neanderthals, with their small populations, could have been absorbed by the much larger populations of modern Homo sapiens. It is possible that differences in behavior rather than biological sterility contributed to low or non-existent interbreeding. But another possibility is that the Cro-magnons that have interbred with the Neanderthals are no longer among us. When agriculture came into Europe, bringing the late stone-age, the hunter-gatherers that lived in Europe first may have been driven away, or have in their turn been absorbed by the larger population of newcomers. Based on an Oxford University 2001 study of the gene that results in red-headedness, some commentators speculated that Neanderthals had red hair and that some red-headed and freckled humans today share some heritage with Neanderthals; however, other researchers disagree, and the scientists who conducted the study claim this is a misinterpretation of their findings.
In November 2006, a paper was published in the U.S. journal Proceedings of the National Academy of Sciences, in which a team of European researchers report that Neanderthals and humans interbred. Co-author Erik Trinkaus from Washington University explains, "Closely related species of mammals freely interbreed, produce fertile viable offspring and blend populations." The study claims to settle the extinction controversy; according to researchers, the human and neanderthal populations blended together through sexual reproduction. Trinkaus states, "Extinction through absorption is a common phenomenon." and "From my perspective, the replacement vs. continuity debate that raged through the 1990s is now dead".
Unable to adapt
European populations of H. neanderthalensis have been traditionally thought to be adapted to a cold environment, and thus may have had problems adapting to a warming environment. This may or may not be the case, although it has been suggested that the difference in cold-adaptation between Neanderthals and H. sapiens may have been minor. Another problem with this idea is that the glacial period of our ice age ended about 10,000 years ago, while the Neanderthals went extinct about 24,000 years ago.
Another possibility has to do with the loss of the Neanderthal's primary hunting territory - forests. The Neanderthals hunted by stabbing their prey with spears (as opposed to throwing the spears at their prey). They were also far less mobile than modern humans. So when the forests were gradually replaced by flat lands, the Neanderthals would have had great difficulty hunting. In the open they would not have been able to stalk their prey, their stabbing weapons would have been largely useless, and they - unlike modern humans - could not easily chase their prey. Also, modern humans are omnivores. The way the Neanderthals were built suggests that they need a lot of energy. Injuries in found skeletons suggest that both males and females hunted. Together, this suggests that Neanderthals ate meat only, and were therefore less adaptable. The same thing is seen in the wolf family, where smaller species, like foxes, usually held out longer than the larger species, which are dependent on big prey and specific hunting environments like Neanderthals. Homo sapiens, which hunted large prey but did not depend on them for survival, may have helped them into extinction this way.
Division of labor
In 2006, anthropologists Steven L. Kuhn and Mary C. Stiner of the University of Arizona proposed a new explanation for the demise of the Neanderthals. In an article titled "What's a Mother to Do? The Division of Labor among Neanderthals and Modern Humans in Eurasia", they theorise that Neanderthals did not have a division of labor between the sexes. 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 contrasted with humans who were better able to use the resources of the environment because of a division of labor with the women going after small game and gathering plant foods. In addition because big game hunting was so dangerous this made humans, at least males, more resilient (see also Peter Frost's theory on the origins of European blond hair).
Anatomical Differences and Running Ability
Researches including Karen L. Steudel of the University of Wisconson have proposed that because Neanderthals had limbs that were shorter and stockier than humans, and because of 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.  This would have given modern humans a huge advantage in battle. Other researchers, like Yoel Rak, from Tel-Aviv University, Israel have noted that the fossil records show that Neanderthals 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.  Applying Occam's Razor the anatomical theory is superior to the division of labor theory because anatomical theory relies on direct evidence than can be proven directly from Neanderthal fossils, whereas the division of labor theory relies on speculation about Neanderthal societies than cannot be proven directly from the fossil record.
In popular culture
- Jean M. Auel's book series Earth's Children, especially the first book The Clan of the Cave Bear, fictionally explores the lives and culture of co-existing Neanderthals and Cro-magnons in eastern Europe.
- The fantasy novelist Jack Vance, in his Lyonesse Trilogy, mentions that cannibal Neanderthals battled with the ancient ancestors of the Ska, an imaginary culture or subspecies of Homo sapiens.
- Science fiction novelist Larry Niven speculates that encounters with Neanderthals was the basis for human folklore about trolls, ogres, and suchlike.
- Michael Crichton's novel, "Next" contains a series of articles describing the extinction of the apparently more intelligent Neanderthals with comparison with Homo sapiens.
- William Golding's second novel, The Inheritors reconstructs the life of Neanderthal interaction and subsequent extinction with a "newly-evolved" malevolent Homo sapiens species.
- Dance of the Tiger is a fictional short story written by Björn Kurtén which explores Neanderthal and Cro-magnon integration.
- The bestselling 1996 paperback novel Almost Adam by Petru Popescu follows a group of scientists who find a tribe of Neanderthals still alive today in the remote Caucasus Mountains.
- Finlayson, C., F. G. Pacheco, J. Rodriguez-Vidal, D. A. Fa, J. M. G. Lopez, A. S. Perez, G. Finlayson, E. Allue, J. B. Preysler, I. Caceres, J. S. Carrion, Y. F. Jalvo, C. P. Gleed-Owen, F. J. J. Espejo, P. Lopez, J. A. L. Saez, J. A. R. Cantal, A. S. Marco, F. G. Guzman, K. Brown, N. Fuentes, C. A. Valarino, A. Villalpando, C. B. Stringer, F. M. Ruiz, and T. Sakamoto. 2006. Late survival of Neanderthals at the southernmost extreme of Europe. Nature advanced online publication.
- Gravina, B., P. Mellars, and C. B. Ramsey. 2005. Radiocarbon dating of interstratified Neanderthal and early modern human occupations at the Chatelperronian type-site. Nature 438:51-56.
- Mellars, P. 2006. A new radiocarbon revolution and the dispersal of modern humans in Eurasia. Nature' 439:931-935.
- "Red-Heads and Neanderthals". May 2001. Retrieved 2005-10-28.
- "Nicole's hair secrets". 2002-02-10. Retrieved 2005-11-02. Check date values in:
- Humans and Neanderthals interbred
- Modern Humans, Neanderthals May Have Interbred
- Nicholas Wade, "Neanderthal Women Joined Men in the Hunt", from The New York Times, December 5, 2006
- 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
- Serre; et al. (2004). "No evidence of Neandertal mtDNA contribution to early modern humans". PLoS Biology. 2 (3): 313&ndash, 7. PMID 15024415.