Thus far, a tiny finger bone and two back teeth in a cave in the Altai Mountains are the only known remains of the Denisovans – a humanoid that Max Planck researchers have identified solely through their genetic material. Scientists of the Max Planck Institute for Evolutionary Anthropology in Leipzig together with an international team of researchers have analysed the genome of the Denisovans with a precision that has not been attained before. This has opened up a wealth of new insights into the developmental history of humans for Matthias Meyer from the Max Planck Institute in Leipzig.
What is so exceptional about the results that have been published now?
Matthias Meyer: The genetic material of an extinct organism has never been decoded before in such detail as that of the Denisovans. And that, even though the bones with the DNA had lain in a cave for over 50,000 years. The quality of the data is as good as if you were to have your own genome analysed today. We can even differentiate between the maternal and paternal chromosomes. A comparison of both sets of chromosomes, or genomes, shows us that the parents of our Denisovan were genetically very similar – although they were not related to one another. We can conclude from this that there cannot have been very many of these people.
The developmental history of humans is becoming more and more complicated as a result of your findings: Denisovans, Neanderthals, and modern humans. Who actually descended from whom?
We did not descend from either the Denisovans or the Neanderthals. The analyses we did on the genotypes of these three humanoid groups revealed that our most recent common ancestor lived about 500,000 years ago, as a rough estimate. The ancestor of the Denisovans and Neanderthals then developed separately from modern humans and begot both of these humanoids – thus, they are siblings of a sort. Homo sapiens first originated 120,000 to 200,000 years ago. The developmental history of humans therefore has actually become quite colourful.
The Out-of-Africa Theory says that the origins of humanity lie in Africa. How did our ancestors then spread from there?
The most plausible scenario at present is that there were two waves of transmigration out of Africa: the group of prehistoric humans, from which the Neanderthals and Denisovans originated, migrated out of Africa approximately half a million years ago. The Neanderthals settled primarily in Europe to as far away as Central Asia, while the Denisovans lived in East Asia.
Homo sapiens, i.e. modern man, first left the African continent during a second wave of migration fifty to one hundred thousand years ago and moved to East Asia.
How probable is it that there were further humanoids, and that our ancestral tree will have to be revised again?
That is entirely possible. The discovery of a small finger bone from the Denisovans was pure chance. It shows absolutely no external difference from the finger of a modern human or Neanderthal. Only the genetic investigation revealed what kind of extremely unusual find we were holding in our hands. The more samples we investigate from a molecular-biological standpoint, the greater the probability of discovering an additional humanoid as well, naturally.
But besides the Neanderthals and Denisovans, we already know of a fourth form now that lived contemporaneously with modern humans, the Homo floresiensis which was found on the Indonesian island of Flores in 2004. It is still not clear where it should be placed in the ancestral tree. Unfortunately, the tropical climatic conditions on Flores are unfavourable for preserving DNA. I therefore have little hope of being able to analyse the genome.
The findings that the different humanoids interbred with one another raised quite a stir. How much Neanderthal or Denisovan is within us today still?
That depends on what part of the planet you come from. We have determined that one percent of the DNA in a European matches the DNA of the Neanderthal. Surprisingly, the 1.8% match with East Asians is significantly higher, although the centre of Neanderthal settlements was mainly in Europe. Therefore, Homo sapiens and Neanderthals possibly intermingled more frequently in Asia than in Europe.
In contrast, the Denisovans have left their traces behind only in the genetic material of various ethnic groups in Southeast Asia. Thus, for example, about three percent of the genome for the people of Papua, New Guinea or the Aborigines originated from Denisovans.
Do these figures mean that this kind of intermingling only took place infrequently?
It was certainly the exception. But it is entirely possible that the portion of foreign DNA in our genome was originally higher and that parts of it disappeared again through natural selection for instance.
Did Neanderthals and Denisovans also intermingle with one another?
That's something we do not yet know. In order to determine that, we also have to analyse the Neanderthal genome just as precisely as we have successfully done in the case of the Denisovans.
How great is the difference between the Denisovans and us?
We have found about 100,000 locations in the genome of the majority of humans living today that are different from the Denisovans. That is not as many as it sounds though, because only 260 of them are located in regions that provide information for proteins. It is notable that the changes took place more so in genes that involve the development of the nervous system, the way the brain functions, as well as the nature of the eyes and skin.
One example of a shift in the genetic areas between two types is the EVC2 gene. If it mutates in modern humans, it triggers Ellis-van Creveld Syndrome – a rare disease in which the patients have malformed teeth, among other things. Only future research will be able to determine whether this is the reason for an altered tooth shape in Denisovans. We will therefore be investigating areas such as these even more precisely in future. In any case, we can learn a great deal about what differentiates us from our nearest relatives by comparing the genomes.
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