Human evolution is a complicated web of ancestry that has puzzled paleontologists and geneticists alike ever since the advent of fossil study. A newly discovered thighbone from a cave in Spain, while adding current information to this increasingly mysterious brainteaser, complicates the puzzle even further.

At first thought to have been the femur of an early Neanderthal – a closely related human ancestor that lived from 200,000 to about 30,000 years ago – a new study in Nature led by Matthias Meyer from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, finds evidence that DNA from the ancient bone says differently. Apparently the bone belonged to a human predecessor that lived 400,000 years ago – making it the oldest human ancestor fossil with viable DNA evidence ever discovered.

The bone fossil was discovered in a cave known as Sima de los Huesos – in Spanish: the pit of bones – alongside a number of other fossils belonging to ancient primates. In fact, since the 1970’s, over 25 almost complete human skeletons have been found on the site.

Meyer and his group found bone matter suitable for DNA testing deep within the bone, and closer analysis revealed that its genes were closer to those of Denisovans – a prehistoric group of early humans who were thought, until this recent find, t have lived only in Eastern Asia.

Paleontologists are unsure what exactly this new piece of evidence tells us for sure about the story of human ancestry. It could be that the bone was the femur of a new species – a lineage that then diverged into Neanderthals and Denisovans around 300,000 years ago, when Neanderthals migrated West and Denisovans decided to take the path to what is now Eastern Asia.

Another explanation for the lack of Neanderthal DNA similarity could be that the genes present in the thighbone fossil were existent in very early Neanderthals, but we haven’t found old enough Neanderthal specimens to classify such DNA as strictly Neanderthalian.

Or perhaps the thighbone is from Homo erectus, a well-studied early human that predates both Neanderthals and Denisovans.

Either way, paleontologists now have another piece of the puzzle to help them piece together the intricate puzzle that is our family tree.

Source: Meyer, M., Fu, Q., Aximu-Petri, A., Glocke, I., Nickel, B., Arsuaga, J. L., … & Pääbo, S. (2013). A mitochondrial genome sequence of a hominin from Sima de los Huesos. Nature.

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Published On: December 26, 2013

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