Genetic Hybrids: Tales of 3 Lost Peoples Who Were Our Ancestors

This post is something I wrote for some friends:

As most of you know, one of my hobbies is my own take on genealogy:  the growing body of literature coming out of genetics studies that tell us about human prehistory.  There lately have been a bunch of new studies that I thought I'd put together for your reading pleasure:

Genetic Hybrids:  Tales of 3 Lost Peoples Who Were Our Ancestors:  New genetic evidence suggests that we modern humans are a hybrid species of sorts.  Most of our genome derives from our Homo sapien ancestors who evolved in Africa.  When the first modern humans left Africa, they encountered two other hominid species:  Neanderthals in western Asia and Europe; and Denisovans in Asia.  The discovery of the Denisovans was only announced in a 2010 paper after geneticists were stunned to find a finger bone and a few teeth -thought to be Neanderthal fossils- actually were a completely different yet related species.  Denisovans are named for the Denisova Cave in which these fossils were discovered.  This cave is in the Altai Mountains in Siberia.

Genetic evidence points to some interbreeding of Homo sapiens with Neanderthals and Denisovans.  2-6% of the DNA of non-Africans today appear to come from Neanderthals.  Indigenous sub-Saharan Africans usually do not show any Neanderthal DNA in their genomes.  It appears Homo sapiens' immune systems benefited from genes from our Neanderthal ancestors.   

One part of the diaspora out of Africa likely spread along the shores of the Indian Ocean from Africa to Arabia -> India -> Indonesia/Melanesia and finally Australia.  This group appears to have encountered the Denisovans because Melanesians have the highest percentage of Denisovan DNA in their genome (up to 6%).  Later settlers into Asia do not show much Denisovan ancestry. So the Denisovans either blended into a larger Homo sapiens population or died out before the next waves of Africans moved into Asia.  A 2013 study now suggests that Homo sapiens encountered the Denisovans not in Asia but in New Guinea or Australia after both groups successfully navigated the Indonesian sea barrier called Wallace's Line.

Finally, last year some geneticists published the results of a study of the DNA of various sub-Saharan African hunter-gatherer populations.  In their analysis they found evidence of an unknown third ancestral hominid who appears to have interbred with Homo sapiens.  Just as most Africans do not have Neanderthal or Denisovan ancestry, this mysterious third hominid species' DNA has so far only been found among these hunter-gatherer peoples in Africa. 

There are no fossil records for this 3rd species.  It doesn't even have a name yet.  One Stanford geneticist argues that the DNA doesn't point to a lost 3rd hominid people but reflects the DNA of our earliest Homo sapien ancestors.  For most African and all non-African humans, mutations have obliterated this original DNA.  So figuring out the answer to this is ongoing.

For Christmas I had my full genome analyzed (some people buy guns or handbags...I buy genetic tests...go figure).  My results came back last week and apparently my genome is 1.6% Neanderthal and an additional 1.6% Denisovan.  I was tickled to have a little bit of the rare Denisovan in me but a bit sad I wasn't more Neanderthal. :(