Evrim Yazgin
Cosmos science journalist
Research into the shape of Neanderthal inner ears challenges the theory that the extinct human species originated out of an evolutionary event that led to a loss of part of their genetic diversity.
The findings, published in Nature Communications, are based on fossils from across Europe and Western Asia.
Unlike modern humans, Neanderthals never lived in Africa. Neanderthals evolved in Europe after an even older human ancestor had already made its way out of Africa. This “pre-Neanderthal” population lived in Eurasia between 500,000 and 250,000 years ago.
Neanderthals themselves emerged about 250,000 years ago before dying out about 40,000 years ago, soon after the arrival of Homo sapiens to Europe.
It was long believed that there were no significant changes in Neanderthal genetics over this time. Prior analysis of ancient Neanderthal DNA showed this assumption was incorrect.
In fact, a genetic “bottleneck” due to a drastic reduction in the population occurred about 110,000 years ago. This led to a decline in genetic variation.
Scientists had also assumed that an earlier bottleneck event led to the origin of Neanderthals. From this, it was assumed that Neanderthals had lower genetic diversity than their pre-Neanderthal ancestors.
The new research sought to answer the question of how Neanderthals originated. The study focused on 2 fossil collections.
One is the Sima de los Huesos site of Atapuerca near the town of Burgos in Spain. The site has the largest sample of pre-Neanderthal fossils and dates to 430,000 years ago.
The other site is Krapina in Croatia. It is one of the biggest early Neanderthal collections and dates to 130,000–120,000 years ago.
The researchers compared the semicircular canals of the inner ears – bone structures responsible for our sense of balance – from both sites. They also compared them to other Neanderthals from different ages and other parts of Eurasia.
Later, or “classic”, Neanderthals had lower diversity in their inner ear bones than pre-Neanderthals and early Neanderthals. This matches up with previous palaeo-genetic data. But no such drop in inner ear bone diversity was seen between the pre-Neanderthal and early Neanderthal populations, challenging the idea that there was a genetic bottleneck associated with the origin of Neanderthals.
“By including fossils from a wide geographical and temporal range, we were able to capture a comprehensive picture of Neanderthal evolution,” says co-author Mercedes Conde-Valverde from the 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.”
“We were surprised to find that the pre-Neanderthals from the Sima de los Huesos exhibited a level of morphological diversity similar to that of the early Neanderthals from Krapina,” comments lead author Alessandro Urciuoli from the Autonomous University of Barcelona.
“This challenges the common assumption of a bottleneck event at the origin of the Neanderthal lineage.”
