Researchers at deCODE genetics and their colleagues at the Max Planck Institute and the Universities of Denmark and Iceland have published the first study that used genome sequence data from an entire population to analyze the current crossing sequence of modern and ancient humans over 50,000 years ago.
The article was published in the renowned journal Nature and supports preliminary estimates that most people outside Africa have about two percent old ancestry, mainly based on the results of repeated contact and interbreeding between various groups of Homo sapiens and various Neanderthals.
The results also show genomic sequences from Denisovans that are more important than previously expected - another ancient human species that interbred with both Neanderthals and Homo sapiens.
Modern humans of non-African descent have a small Neanderthal component in their DNA. Some other members of the non-African population, depending on where they live, also have some of their DNA inherited from the people of Asia known as Denisovans.
The fact that genes have been passed down through the generations confirms that crossbreeding must have taken place somewhere. However, the only known place where the fossil remains of both Denisovans and Neanderthals have been found is in Denisova Cave in the Altai Mountains.
It is known that Neanderthals and Denisovans simultaneously lived in some regions of Eurasia: Neanderthals in the west and Denisovans in the east.
Their traces are lost about 40 thousand years ago - as scientists believe, it was then that both species became extinct, giving way to modern man.
As Neanderthals migrated eastward, they may have occasionally encountered Denisovans as well as early homo sapiens.