Neanderthals may have gone extinct due to chance, and not, as some researchers previously thought, due to competition for resources with Homo sapiens, according to a study published on Wednesday (November 27) in PLOS ONE. Simulations of population dynamics, carried out by researchers in the Netherlands, suggests that inbreeding, small population sizes, and a pinch of misfortune could have been sufficient to wipe out our hominin cousins around 40,000 years ago.
“The standard story is that Homo sapiens invaded Europe and the near east where Neanderthals were living and then we outsmarted them or outnumbered them,” study coauthor Krist Vaesen of Eindhoven University of Technology tells The Guardian. “The main conclusion of our work is that humans were not needed for the Neanderthals to go extinct. It’s certainly possible that it was just bad luck.”
Vaesen and colleagues built a simulation of Neanderthal populations, which totaled between 5,000 and 70,000 individuals by the time H. sapiens arrived in Eurasia around 60,000 years ago.
In their model, the researchers included three factors that could affect population dynamics: inbreeding, which lowers biological fitness; Allee effects, which account for the cost of having insufficient adults to raise the next generation and other consequences of small population sizes; and chance fluctuations in population characteristics such as birth and death rates.
The team found that, combined, these factors were sufficient to drive simulated Neanderthal populations to extinction within a few millennia. “Our results are consistent with a scenario in which a small population of Neanderthals persists for several thousands of years, and then, due to a stroke of bad luck, disappears,” the authors write in their paper.
Vaesen tells Cosmos that our human ancestors could have accelerated the process indirectly, perhaps by making it “much more difficult for Neanderthals to migrate among subpopulations.” Interspecies breeding between Homo sapiens and Neanderthals may also have reduced the latter’s population growth, by reducing opportunities for Neanderthals to replenish their own numbers.
Penny Spikins, an archaeologist at the University of York in the UK who was not involved in the work, tells The Guardian that the effects the team studies may explain Neanderthals’ demise. However, she notes that the authors built their simulations based on knowledge of modern humans, and so might have failed to accurately capture the population dynamics of Neanderthals.
“We have yet to fully understand these effects,” she tells The Guardian, “and so it may be a little premature to entirely absolve ourselves of ‘survivor’s guilt.’”
Catherine Offord is an associate editor at The Scientist. Email her at firstname.lastname@example.org.