Neanderthals did not go extinct because of climate change and competition with modern humans—they were doomed to be wiped out as a result of the evolutionary phenomenon of "random species drift."
In a study published in the journal Nature Communications, Oren Kolodny and Marcus Feldman, from Stanford University, developed an alternative model of Neanderthal extinction that focuses on changes in population numbers of a species based on random events rather than selective advantage—where one species outperforms another because of specific traits or characteristics.
The findings show that regardless of whether modern humans had evolutionary advantages over Neanderthals, the latter was always going to be replaced by the former.
Neanderthals emerged in Europe around 400,000 years ago. They began crossing paths 300,000 years later, as humans made their way into Neanderthal territory. Eventually, these encounters became more and more common and, for between 10,000 and 15,000 years, the two species co-existed and interbred—2 percent of our DNA comes from Neanderthals.
Around 38,000 years ago, Neanderthals went extinct. Over recent decades two main theories of what caused their demise have emerged. The first is climate change—their decline coincides with a period of extreme cold in Western Europe that would have placed a huge amount of stress on the species. The other is competition with modern humans—our bigger brains and better adaptations to the environment at the time meant Neanderthals didn't have a chance.
These two factors are not mutually exclusive and it is often suggested a combination of the two led to their downfall. Kolodny and Feldman's new model says that irrespective of climate change and humans being at an evolutionary advantage, Neanderthals were always going to go extinct.
In the study, the pair assumes that Neanderthals and humans were equals in terms of adaptations. They then looked at waves of migration, as small groups of humans moved into Europe from Africa. As the two groups came into contact, one would go extinct. While very gradual, repeated waves of migration eventually led the Neanderthal population to plummet before disappearing entirely.
As a result of "species drift," humans slowly replaced Neanderthals until they dominated the landscape. This replacement, the researchers say, "was certain to occur, even in a selectively neutral setting, given the estimated migration pattern near the onset of the interaction between the two populations," the researchers wrote.
"We have also demonstrated that even if bidirectional migration between Europe and Africa had occurred, [modern humans] would have been extremely likely to eventually replace Neanderthals, given the estimated differences in population size between the species, in favor of [modern humans]."
