Today we mostly think about animals going extinct, but not really about humans having the same fate. This is because every single species of human before us has already done so. We, modern humans, Homo sapiens sapiens, are the last members of our race. Every other human species that walked the Earth at some point is now extinct.
As our ancestors, the Homo sapiens, were making their way from Africa to Eurasia, they ran into other groups of humans which weren’t members of the same race. As multiple groups met in Eurasia, they hooked up, as humans tend to do. And now we finally have proof that humans interbred with Neanderthals and Denisovans.
Since clues related to this could yield information about the human genome that would not be able to be revealed in any other way, multiple studies have been directed at investigating the genome left in our DNA by that long-ago species interbreeding. And as it turns out, most humans except for those in Africa have about one to four percent of their DNA belonging to Neanderthals or Denisovans.
But while Neanderthal genes have been studied before, Denisovans weren’t so much. This is because of the incredibly little amount of fossil remains found f this elusive species. Only a tooth and a finger joint were found in a Russian cave, bot belonging to a Denisovan scientists refer to as Woman X.
Discovering that the genomes of modern day humans found in the area known as Melanesia (Fiji, Vanuatu, Solomon Islands, Papua New Guinea, and New Caledonia) contain between 1.9 and 3.4 percent Denisovan DNA, a team of scientists deeply investigated the matter.
According to Rasmus Nielsen, a researcher from the Center for Theoretical Evolutionary Genomics at the University of California who was not part of the study,
The most exciting new thing about the paper is that it confirms that there have been multiple Neanderthal introgression events independently on several different human evolutionary lineages.
Instead of thinking of Neanderthal admixture as something that happened just once or twice, we are now forced to consider the possibility that there has been extensive admixture between Neanderthals and humans in the entire range in which they overlapped.
These important findings were made as the scientists realized that these archaic sequences are splattered all throughout the genome, in some places even making up for as much as more than half the entire sequence. Most of these are related to the immune system.
This shows that the ancient humans started interbreeding as it was a good way to get the necessary genes to survive these long treks, and most of them got rid of them through natural selection when they stopped being necessary. It’s a very efficient way to adapt to environmental conditions.
Image source: Wikimedia