A new study published in Scientific Reports has added some surprising details to the complicated death of Neanderthals. It further implies that the resulting genetic dilution from interbreeding with Homo sapiens was extensive and contributed to their extinction. Neanderthals originated in Eurasia approximately 400,000 years ago. For thousands of years, they were the undisputed kings of the hominin jungle of Southeast Asia, until modern humans first appeared in the region roughly 40,000 years ago.
The research further shows that Neanderthal populations were made up of these small and isolated groups which would’ve introduced problems like inbreeding depression. This demographic isolation led to low population growth, challenges in mate choice, low fecundity, and high mortality. Meanwhile, over the course of millennia, Homo sapiens moving out of Africa rapidly spread across Eurasia. Throughout their long migration, they mixed and reproduced with Neanderthals, creating a genetic cocktail.
Population geneticists employed a mathematical model blending neutral species drift with population genetics. They modeled what happened when small-scale immigrations of Homo sapiens began overwhelming Neanderthal tribes. Together, these finds show the pivotal role these early migrations had in supplanting almost all Neanderthal genes. Geologically speaking, this process occurred incredibly quickly – within a span of 10,000 to 30,000 years.
Evidence of interbreeding and genetic introgression supports the notion that H. sapiens and Neanderthals interacted extensively over thousands of years. Thus, the interaction of genetic variation, demographic history, and environment probably shaped the complexity of and factors leading to Neanderthal extinction, the study notes.
Nevertheless, modern humans as a whole still carry a substantial portion of Neanderthal genetic material. This interbreeding supports the idea that there was a lot of gene flow between the two species. “The present modern human genome reveals multiple instances of genetic introgression with other hominins,” the authors highlight. “Modern humans still retain a considerable amount of Neanderthal genetic material, at the species level if not in every individual.”
Although genetic dilution is portrayed as the primary cause of the Neanderthals’ disappearance, the paper recognizes other possible factors at work. “Although this model provides a possible robust genetic explanation, it is important to note that it does not exclude other possible contributing factors that were not considered in our approach, such as environmental changes, competition, or demographic fluctuations,” the researchers clarify.
This study contributes to an active debate on the role of Homo sapiens in Neanderthal extinction. Scholars have long debated whether competition or inter-species interactions between the two groups played a major role in Neanderthal survival. The combination of genetic, demographic and environmental factors remain an area of great interest for future study.