Recent DNA research indicates that Neanderthals experienced a significant reduction in genetic diversity approximately 110,000 years ago, a troubling precursor to their extinction around 70,000 years later. A groundbreaking study has revisited the concept of this genetic “bottleneck” by examining an unusual aspect: the ears of Neanderthals.

Led by paleontologist Alessandro Urciuoli from Universitat Autònoma de Barcelona, an international team investigated the semicircular ear canals—three small tubes in the inner ear responsible for maintaining balance—across various time periods to identify notable shifts in genetic diversity. Their findings confirmed the occurrence of a bottleneck event in Neanderthals, as detailed in a study published on February 20 in the journal Nature Communications. While this genetic bottleneck didn’t directly lead to the Neanderthals’ extinction, it potentially set them on a perilous trajectory, according to the research.

“The inner ear structures are governed by strict genetic controls and are completely formed at birth,” explained Rolf Quam, an anthropologist from Binghamton University who contributed to the study, in a university statement. “This tight regulation makes variations in the semicircular canals an excellent indicator for studying the evolutionary connections between species, as any differences observed in fossil specimens reflect underlying genetic variations. This research represents an innovative method for assessing genetic diversity within Neanderthal populations.”

Quam and his research team analyzed three distinct groups of Neanderthals, comparing the semicircular canals of early Neanderthals and “pre-Neanderthals” to those of “classic” Neanderthals. The Atapuerca fossils, estimated to be around 400,000 years old and identified as pre-Neanderthals, were found in Spain. The early Neanderthals—referred to as the Krapina fossils—date back roughly 130,000 years and were discovered in Croatia, while the “classic” specimens span various regions and eras.

The results revealed a notable decrease in the morphological diversity of the semicircular canals among classic Neanderthals compared to their earlier counterparts. This finding aligns with prior DNA analyses that indicated a significant decline in genetic variation between early and classic Neanderthals.

“By incorporating fossils from a diverse geographical and temporal range, we were able to achieve a more comprehensive understanding of Neanderthal evolution,” stated Mercedes Conde-Valverde, a paleontologist from the Universidad de Alcalá and co-author of the study. “The observed reduction in diversity between the Krapina specimens and classic Neanderthals is particularly striking, providing compelling evidence of a bottleneck event.”

However, the researchers made an unexpected discovery. Though there is widespread consensus that Neanderthals experienced a substantial loss of diversity at the onset of their evolution, the team anticipated clearer differences in morphological variation between pre-Neanderthal and early Neanderthal semicircular canals.

“We were surprised to find that the pre-Neanderthal specimens from Sima de los Huesos exhibited a level of morphological diversity comparable to that of early Neanderthals from Krapina,” Urciuoli remarked. “This challenges the existing assumption of a bottleneck event occurring at the beginning of the Neanderthal lineage.” This inconsistency is likely to spur further investigations into the demographics of early Neanderthals, particularly regarding how this separation from our own ancestors was influenced.

Neanderthals became extinct around 40,000 years ago, though the reasons behind their disappearance remain somewhat unclear. We know that anatomically modern humans, or Homo sapiens, interbred with Neanderthals, leading to their eventual integration into our species. The finding that Neanderthals faced a reduction in genetic diversity and small populations aligns with the latest research.

A population bottleneck occurs when there’s a sudden and dramatic decrease in population due to factors such as environmental disasters, climate shifts, and limited food resources. While the study does not pinpoint a specific cause for the Neanderthal bottleneck 110,000 years ago, the decreased genetic diversity likely rendered them more susceptible to ongoing pressures, hindering their adaptability from an evolutionary standpoint.

Although it took some time for Neanderthals to face extinction following this mysterious population decline, it likely sealed their fate as suggested by the new findings. Ultimately, this research enhances our understanding of the demographic evolution of our ancient relatives—whose genetic legacy continues to influence modern humans today.