Only between 1.5% and 7% of the modern human genome is “exclusively human”, according to a new algorithm analysis of the Neanderthal, Denisovan and Homo sapiens genomes.
The results are published in the journal ‘Science Advances’ and also provide evidence of multiple explosions of adaptive changes specific to modern humans in the last 600,000 years, involving genes related to the development and functioning of the brain.
The research is led by scientists from the University of California (USA), who have found it difficult to determine which genes in the modern human genome were transmitted by our hominid ancestors which are exclusively ours, summarizes the magazine.
One particular obstacle is that humans (Homo sapiens) harbor Neanderthal alleles -An allele is each of the two or more versions of a gene. And they do so both because of the interbreeding between human and Neanderthal populations and because of the incomplete classification of lineages, that is, alleles that predate the separation between homo sapiens and Neanderthals but are not found in all humans.
To avoid these problems, Nathan Schaefer and his colleagues developed a improved algorithm -called SARGE-, which more effectively highlights alleles inherited from mixing humans with Neanderthals.
The researchers analyzed 279 modern human genomes, two Neanderthal genomes and one Denisovan genome, and traced Neanderthal and Denisovan ancestry and the absence of both in modern human genomes. This allowed identify specific mutations in humans and determine that these mutations arose in two separate explosions: one about 600,000 years ago and the other about 200,000 years ago. Many of these mutations appear to affect genes involved in neuronal development and function.
The calculations also suggest that at least one wave of Neanderthals intermingled with the ancestors of non-Africans and points to unique Neanderthal and Denisovan genomic regions in South Asia.