What the Fossil Record Reveals About Early Human Hybridization
On combining morphological and genomic evidence to evaluate hybridization in late Pleistocene Western Eurasian hominins
According to paleogenetic research, the history of our species looks more like cris-crossing braids or computer networks. Admixture in ancient human lineages is suggested by the fact that many modern humans contain Neanderthal DNA in their genes. Furthermore, hybridization with Neanderthals and other prehistoric species happened more than once. With Denisovans in the play, it is obvious that the history of humanity was more nuanced than previously assumed.
It is crucial to examine the effects of such hybridization using a variety of sources of evidence. Since ancient DNA is rarely preserved well in fossil specimens, so researchers must identify potential hybrids from their skeletons. Understanding our complicated past and what makes us human depends on this.
Using fossil skulls, Katerina Harvati and Rebecca R. Ackermann have previously examined the effects of hybridization and identified certain probable hybrids. In the journal Nature Ecology and Evolution, they have released new research combining the fossil record with ancient DNA.
In order to accomplish this, the researchers looked at numerous fossilized remains of prehistoric humans from the Upper Paleolithic of Eurasia, which date to between 40 and 20 thousand years ago. Numerous of these ancient individual remains have yielded ancient DNA evidence, which reveals a minor amount of Neanderthal heritage in their genes, indicating recent hybridization with this population. Their skull bones were compared to samples from Neanderthals, early modern humans from Africa, and more recent modern humans. The mandible, the braincase, and the face were the three areas of the skull that the researchers looked at for telltale evidence of hybridization. Their research revealed that whereas faces did not exhibit signs of hybridization, braincases and jaws did.
The researchers also took into account whether the amount of Neanderthal ancestry in the individuals with known genetic backgrounds matched any skeletal evidence of hybridization. The absence of this indicates that specific genetic variations may be more significant than the total percentage of Neanderthal ancestry.
The authors also noted that some of the samples under investigation might have been hybrids, including those from the Middle East, which is well known to have been a point of contact between the groups, as well as from elsewhere, including Western and Eastern Europe.
This was a pioneering study in its field.
When faced with novel or changing environmental conditions, hybridization can promote particularly rapid evolution because it introduces new variety and new combinations of variation. Therefore, the authors speculate that hybridization may have given early humans genetic and anatomical traits that offered them significant benefits as they migrated from Africa throughout the globe, giving rise to our physically diversified and hardy species.
Harvati, K., Ackermann, R.R. Merging morphological and genetic evidence to assess hybridization in Western Eurasian late Pleistocene hominins. Nat Ecol Evol (2022). https://doi.org/10.1038/s41559-022-01875-z