Hominid 1.8 million-year-oldfossil

Lumping or splitting in the fossil record
November 2013

The 1.8-million-year-old skull was found in 2005 in the Republic of Georgia

Rarely does pure science take top billing in the news, but this past month saw a notable exception. The front page of the New York Times was occupied by the image of an ancient hominid skull caked in dirt. This 1.8 million-year-oldfossil, excavated in the Republic of Georgia, represents the oldest complete adult cranium of a hominid yet discovered. That alone would be significant news, but the context in which the fossil was preserved adds even more weight to the discovery...

Where's the evolution?

The new cranium was found in the same location as four other skulls that were deposited around the same time — each in the burrow of an ancient carnivore. Clearly, our ancestors were not at the top of the food chain! But more significant than their grisly deaths is the shapes of their skulls. They are not particularly similar to one another. Each clearly belongs to the Homo lineage, but if they had been found in distinct locations or were from different time periods, they likely would have been classified as different species. Yet, we know that these human relatives were all living in the same place at the same time.

The international team of researchers behind the work contends that all five skulls (and by extension many similar fossils discovered previously in Africa) belong to the same species. They suggest that the physical differences between these fossils simply reflects the normal variation among individuals of the same species — just as you look different from every other human on Earth and individual chimpanzees all look different from one another. In support of their hypothesis, the researchers measured the physical differences between the fossil Homo skulls and found them to be no greater than the range of variation within modern human or chimpanzee populations. Perhaps then, many of our ancient human relatives were erroneously assumed to be of different species based on unimportant differences in shape and because they were found in different localities. The researchers argue that the distinction between fossils assigned to Homo erectus, H. rudolfensis, and H. habilis should be re-examined. They may represent not distinct branches on the tree of life, but a single limb./.../