A new study (in Nature) by an international team (Urciouli, 2025), based in New York, suggests that Neanderthals experienced a dramatic loss of genetic variation during the course of their evolution, foreshadowing their eventual extinction.
The authors found through examination of Neanderthal semicircular canals (of their ears), that they experienced a ‘bottleneck’ event where physical and genetic variation was lost.
Evolution by Darwinian natural selection relies on the presence of genetic variation within a population. This means that individuals within the population exhibit differences in their characteristics, such as traits, genes, or behaviours.
By mixing these variations, inter reproduction will produce ‘stronger’ individuals, who are more likely to survive. Humans (Homo sapiens) are no different.
The Atapuerca fossils – referred to as ‘pre-Neanderthals’ – date to about 400,000 years ago and represent the earliest fossils that anthropologists consider clear Neanderthal ancestors.
The Neanderthals emerged around 250,000 years ago from these populations. They became extinct (quite rapidly) about 40,000 years ago.
The Croatian site of Krapina represents the most complete collection of early Neanderthals and dates to approximately 130,000 years ago. The researchers calculated the amount of morphological diversity (i.e. disparity) of the semicircular canals of both samples, comparing them with each other and with a sample of ‘classic’ Neanderthals of different ages and geographical origins.
“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,” said Quam (one of the authors).
This makes variation in the semicircular canals an ideal proxy for studying evolutionary relationships between species in the past”.
Their research based on ancient DNA samples extracted from fossils revealed the existence of a drastic loss of genetic diversity between early Neanderthals and the later ‘classic’ Neanderthals.
Technically known as a ‘bottleneck’, this genetic loss is frequently the consequence of a reduction in the number of individuals of a population. The ancient DNA data indicate that the decline in genetic variation took place approximately 110,000 years ago.
But what does this mean for modern humans?
Homo sapiens also probably emerged about 200,000 and 300,000 years ago, and started to spread out of Africa 100,000 years ago. They developed a capacity for language about 50,000 years ago.
It is thought that the two types of hominid lived side by side, for about 5000 years. But why did ‘we’ survive, and they did not?
It could relate in part, to lack of variation (due to lack of migration) in ‘them’, and more migration (and hence genetic mixing) in ‘us’.
Homo sapiens is a ‘social animal’ that (generally!) likes each others’ company. This may be key to our ‘success’. And, as part of that, encouraging migration (and inter-marriage) may increase the likelihood of survival of the modern human race.
