Neanderthal, Denisovan DNA Found Near Autism Genes in Modern Humans [View all]

Neanderthal, Denisovan DNA Found Near Autism Genes in Modern Humans
By Joel Hruska on October 18, 2019 at 9:01 am

One of the most interesting questions of hominin evolution is exactly how much of our vanished cousins remains in us. Between 1-4 percent of the modern human genome is derived from Neanderthals everywhere but sub-Saharan Africa. In addition, between 4-6 percent of the modern Melanesian genome has been shown to be derived from a separate species of archaic hominin, Denisovans. Now, a new paper focused on comparing a specific type of genetic variance has found evidence suggesting that Denisovans and Neanderthals made large-scale, long-term positive contributions to the human genome. Our understanding of the impact of these changes is currently limited, but they occur in a rather interesting place.

Most of the studies that compare differences in human populations (or differences between archaic and modern hominins) focus on adaptive single-nucleotide variants (SNV). It was a single nucleotide variation that gave archaic northwest Europeans the ability to digest lactose, and the ability to do so is a textbook case of human natural selection. The image below shows the prevalence of adult lactase persistence as a percentage of the total population.



Image by Joe Roe, Wikipedia

Single nucleotide variations found in the genome of the Tibetan people are associated with greater acclimatization to high-altitude conditions. These originated in the Denisovan genome. While the Denisovan addition occurred much earlier than the adaptation for adult lactase digestion, both of them have been conserved (meaning they have persisted since initial evolution).

This new research isn’t focused on SNVs. Instead, it analyzed the modern Melanesian genome for signs of copy number variants (CNVs). Copy number variation is when the number of copies of an entire gene are different between individuals. Huntington’s disease, for example, is caused when a specific sub-section of the Huntingtin gene is repeated to the point that it causes altered protein production. CNVs are much larger than SNVs and they tend to exert very strong selective pressure. Any evidence of conserved CNVs in the Melanesian population that could be traced to the Denisovan or Neanderthal genomes would, therefore, be evidence that these variants conferred benefits.

More:
https://www.extremetech.com/extreme/300458-neanderthal-denisovan-dna-found-near-autism-genes-in-modern-humans