New Research on Inner Ear of Neanderthals Challenges the Widely Accepted Theory That They Originated After an Evolutionary Event

Time and again, researchers have come across evidence that changes their whole notion regarding evolution. More fossil discoveries mean a greater possibility of gaining evidence that indicates a completely different idea than previously believed. The key is that researchers remain open to the changes and are not rigid. Analysis of fossils from Atapuerca (Spain) and Krapina (Croatia), as well as from various European and Western Asian sites, have put to question a popular theory asserted by experts about the evolution of Neanderthals, stated Phys.org. Findings related to the remains have been published in Nature Communications.

The theory in question is the bottleneck event theory. Past examinations have confirmed that Neanderthals came into existence 250,000 years ago from a European population. This population has been labeled as "pre-Neanderthals." The group supposedly lived on the Eurasian continent between 500,000 and 250,000 years ago. A common assumption has been that a bottleneck event happened with these pre-Neanderthals that led to the creation of Neanderthals. 

'Bottleneck event' essentially refers to genetic loss within the population. This typically happens when there is a sudden decrease in the number of individuals. A decline in numbers brings with it a reduced genetic variation. Hence, the features in the population before the event appear to be more 'advanced' than the one that emerges after it. Multiple experts believed that pre-Neanderthals had more advanced features than the Early Neanderthals. This pattern was not observed in the fossils analyzed within the study. 

The fossils collected from the Sima de los Huesos site of Atapuerca (Burgos, Spain) represented the pre-Neanderthals (430,000 years old), while the specimens from the Croatian site of Krapina belonged to early Neanderthals (130,000–120,000 years old). Researchers examined morphological diversity (i.e., disparity) in the semicircular canals of both samples.

It has already been proven that morphological diversity noted through semicircular canals aligns with the results obtained from DNA comparisons. "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," commented Alessandro Urciuoli, lead author of the study. "This challenges the common assumption of a bottleneck event at the origin of the Neanderthal lineage,” the researcher stated. This implied that no decline in genetic diversity occurred between these two populations. This proves that the previous assertion regarding a bottleneck event causing the birth of Neanderthals is false. Hence, more examinations are needed to arrive at the correct chronology of events that led to Neanderthals.

Researchers noted evidence of a bottleneck event between Early Neanderthals and Classic Neanderthals. Classic Neanderthals refers to the population that came into being after Early Neanderthals. Researchers took into consideration some samples from Classic Neanderthals. The study compared the morphological diversity exhibited by the semicircular canals of all three groups. The results indicated that the morphological diversity of Classic Neanderthals was lower than the remaining two groups. "By including fossils from a wide geographical and temporal range, we were able to capture a comprehensive picture of Neanderthal evolution. The reduction in diversity observed between the Krapina sample and classic Neanderthals is especially striking and clear, providing strong evidence of a bottleneck event," Mercedes Conde-Valverde, co-author of the study, said.