Research technician prepares DNA samples in production lab The 1-3 percent of the Neanderthal genome that survives in modern humans likely helped early homo sapiens adapt to cold Europe by conferring a thicker skin, researchers said Wednesday. It may also have transferred a genetically higher risk for diabetes and lupus.
Humans acquired Neanderthal DNA through interbreeding between 40,000 and 80,000 years ago which resulted in today's European and East Asian populations, scientists believe.
Indigenous Africans have little or no Neanderthal DNA as their ancestors did not interbreed with Neanderthals, who lived in Europe and Asia.
The latest research showed that the Neanderthal's DNA influence on humans was not evenly distributed across the human genome.
Two separate studies, one in the British journal Nature and the other in US-based Science, reported finding concentrations of Neanderthal DNA in genes that influence skin and hair characteristics.
Among other things, these genes influence the production of keratin -- a fibrous protein that lends toughness to skin, hair and nails and may have provided thicker insulation against a colder climate as homo sapiens moved northwards out of Africa, the authors of the Nature paper said.
"Thus, Neanderthal alleles (gene variations) that affect skin and hair may have helped modern humans to adapt to non-African environments," said the study.
"It's tempting to think that Neanderthals were already adapted to the non-African environment and provided this genetic benefit to humans," added co-author David Reich, a genetics professor at Harvard Medical School.
Recent research has concluded that humans trace about two percent of their genome to Neanderthals, but these claim to be the first studies to show the biological effect that the transfer has had on human development.
Apart from the influence on skin and hair, they found, Neanderthals also conferred a risk for conditions like type-2 diabetes and Crohn's disease.
The Nature team, which included scientists from Harvard, the Broad Institute in Cambridge and the Max Planck Institute for Evolutionary Anthropology in Germany, analysed and compared the genomes of 846 people of non-African heritage, 176 Africans, and a 50,000-year-old Neanderthal.
The authors of the paper in Science, using statistical simulations with the genome sequences of 379 European and 286 East Asian individuals and one Neanderthal, came to a similar conclusion on our distant cousin's influence on human skin-related genes.
They further concluded that as much as 20 percent of the Neanderthal genome could be reconstituted today by adding up the totality of the DNA signature still lingering in modern humans.
"If you look at enough individuals (we estimate about 2,000), you could theoretically identify all of the Neanderthal genome that still remains in modern humans," Benjamin Vernot from the University of Washington's department of genome sciences, a co-author of the Science paper, told AFP by email.
"Unfortunately, it's difficult to tell some Neanderthal DNA from human DNA, just because it's still pretty similar to ours. So while there might be 50% of the Neanderthal genome still floating around in modern humans, we were only able to identify 20%."
The team had identified between 300 and 400 genes per individual that were at least partly Neanderthal, he said, but these were different from person to person.
Both studies found regions on the human genome that were devoid of Neanderthal DNA and concluded that certain genes must have been detrimental to humans and could not be tolerated.
These Neanderthal-barren areas were mostly found on genes linked to functioning of the testes and the X chromosome, leading researchers to conclude the genetic exchange had threatened male fertility and had to be undone through a process of natural selection.
Source: AFP