The extinction of the Neanderthals is one of the most intriguing mysteries in paleoanthropology, with researchers speculating everything from shifts in the climate to war with modern humans may have escalated their demise.
Many have wondered if our lost human cousins simply didn’t have enough variety to cope with these changes. A new study backs up the hypothesis that a dramatic decline in the diversity of their genes prior to their extinction is likely to have played a major role.
Carried out by an international team of researchers, the study took a relatively unique approach, using the anatomy of the ear canal and existing Neanderthal genetics to find strong indications of a genetic bottleneck a little over 100,000 years ago.
By comparing the shapes of the ear’s semicircular canal in fossils from across Europe and western Asia with those in modern-day humans, the researchers could gauge the relative variety of body morphologies among different groups of humans.
“The development of the inner ear structures is known to be under very tight genetic control, since they are fully formed at the time of birth,” says anthropologist Rolf Quam, from Binghamton University in New York.
“This makes variation in the semicircular canals an ideal proxy for studying evolutionary relationships between species in the past since any differences between fossil specimens reflect underlying genetic differences.”
Crucial to the study was the Croatian fossil site of Krapina (dating back 130,000 years), and several late Neanderthal sites across France, Belgium, and Israel (dating back 41,000-64,000 years).
Something apparently happened between those two points to affect genetic variation, shown through ear canal shapes. It points to a big reduction in the number of people in a population prior to a point around 40,000 years ago, when the Neanderthals’ time would come to an end.
This study doesn’t examine any possible reasons for the drop in genetic diversity, but a number of factors have been suggested in the past – ranging from climate change to increased competition.
“By including fossils from a wide geographical and temporal range, we were able to capture a comprehensive picture of Neanderthal evolution,” says anthropologist Mercedes Conde-Valverde from Alcalá University in Spain.
“The reduction in diversity observed between the Krapina sample and classic Neanderthals is especially striking and clear, providing strong evidence of a bottleneck event.”
However, while the study helps to answer some questions, it also raises some new ones. The fossils in Krapina showed an unexpected level of diversity, similar to that of much older samples going back some 430,000 years.
That counters the widely held assumption of a much earlier genetic bottleneck contributing to Neanderthal evolution, making a single reduction in diversity shortly before their extinction more likely.
The researchers are keen to apply their ear structure analysis to more samples and sites across the world, which should reveal more about how our distant cousins lived, traveled, and eventually died out.
“The present study represents a novel approach to estimating genetic diversity within Neandertal populations,” says Quam.
The research has been published in Nature Communications.
