Finger points to new human

A team of archaeologists have found the bone of a little finger while digging at Denisova Cave in the Altai Mountain, located in southern Siberia. The size of the bone suggests that it came from a child between five and seven years of age. It is difficult to distinguish between different species of humans based solely on the morphology of a single finger bone. However, the tentative dates put the age of the bone at between 30,000 and 50,000 years ago; a window of time when both Neandertals and modern humans coexisted in Eurasia.

In order to determine which species the little finger came from, Johannes Krause of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany sequenced the complete mitochondrial DNA (mtDNA) from the finger bone and compared its DNA with that of modern humans and Neandertals. What they found surprised everyone involved in the project. The mtDNA of Denisova did not match that of modern humans or Neandertals. In fact it last shared a common ancestor with us and Neandertals in Africa around a million years ago.

We know of three major hominin migrations out of Africa. The first occurred with Homo erectus around 1.9 million years ago, followed by the ancestors of Neandertals sometime between 500,000 and 300,000 years ago, and finally modern humans around 50,000 years ago. This makes the Denisova specimen too late to be part of the Homo erectus exodus and too early to part of the other two.

However, it may be a little premature to declare this a new species of human. Svante Pääbo’s team is already busy sequencing the nuclear DNA of the Denisova specimen. One, albeit unlikely, possibility is that this will turn out to be a representative of an outlier Neandertal population. Previous studies have found a wide diversity in both the morphology and mitochondria of geographically separated Neandertal populations. Until the nuclear DNA has been mapped it is not possible to definitively say if we are really dealing with a new species of human. However, if this does turn out to be the case, it would mean that we shared the globe with at least three other species of humans as late as 40,000 years ago.

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