Pre-Neanderthals once roamed Eurasia around 500,000 years to 250,000 years ago. During the end of that period, pre-Neanderthals slowly began the evolutionary process into early Neanderthals, which would then become the classic Neanderthal.
During that period, most reseachers believed that Neanderthals experienced very little evolutionary change. However, recent findings published in Nature Communications may have just changed that long-held belief. The study examines a specific 'bottlenecking event' that suggests a significant genetic loss occurred between early Neanderthals and classic Neanderthals.
What Is a Bottleneck Event?
In the study of genetics, a bottleneck event refers to a sudden drop in a species population. These dropoffs can be caused by natural disasters, such as earthquakes and floods, as well as pandemics, famine, and human intervention.
The American Bison is an example of a genetic bottleneck event. Before European settlers pushed west into the heart of North America, there were millions of American Bison. However, due to overhunting and slaughter, there were only about 750 bison left in the late 1800s. While the herds have made a comeback, genetic diversity was lost.
The theory of a genetic bottleneck within the Neanderthal lineage isn't specific to this research. According to a study published in Nature Communications, a bottleneck event likely occurred at the beginning of the Neanderthal lineage. Although further study is needed to solidify this theory, the research team used their hypothesis to inform their findings.
Read More: The Fascinating Path of Neanderthal Evolution: Where Did Neanderthals Come From?
When the Neanderthal Bottleneck Occurred
For this study, the research team analyzed DNA samples collected from two fossil collections. The first is from the Sima de los Huesos site in Atapuerca, Burgos, Spain, which is approximately 430,000 years old. It also makes up the largest sample of pre-Neanderthals available in the fossil record. The second is from Krapina, a site in Croatia with the most complete collection of early Neanderthals, which dates back to approximately 130,000 years to 120,000 years ago.
The findings revealed some genetic loss between early Neanderthals and classic Neanderthals. From the data, the research team determined that this bottlenecking event likely occurred about 110,000 years ago. According to the study, the results of the morphological analysis are similar to those obtained through DNA comparisons.
An Ear for Genetic Bottlenecks
For these results, Alessandro Urciuoli from the Institut Català de Paleontologia, Miquel Crusafont from the Universitat Autònoma de Barcelona, and Mercedes Conde-Valverde from the Cátedra de Otoacústica Evolutiva de HM Hospitales y la Universidad de Alcalá, analyzed the semicircular canals -- the fluid-filled canals with the inner ear that help us maintain our balance -- of Neanderthals and measured their morphological diversity.
That's right, the team was able to determine genetic diversity based on Neandertal ears. The results show that classic Neanderthals had a lower morphological diversity of the semicircular canals than pre-Neanderthals.
"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," said Alessandro Urciuoli, lead author of the study, in a press release. "This challenges the common assumption of a bottleneck event at the origin of the Neanderthal lineage."
The results indicate that a bottleneck event did occur, but likely not at the time researchers previously thought it had. These findings are another piece to the Neanderthal evolutionary puzzle.
"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," said study co-author Mercedes Conde-Valverde in a press release.
This article is a republished version of this previously published article.
Read More: Exploring Neanderthal Ancestry: Who Came Before the Neanderthals?
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