It seems as if every time a new fossil hominin is reported in the popular press, someone will claim that it revolutionizes our understanding of human evolution. In the last week, this familiar reaction has followed the publication of the formal description of a fossil excavated at the site of Dmanisi, Georgia (in the Caucasus Mountains, not the Peach state…). Is there reason to be so excited? As is often the case, the answer is yes and no.
On the yes side is the completeness of the skull, which includes not just the brain case, but also an almost complete upper face and a lower jaw. Dmanisi fossil #5 is far and away the most complete Homo skull from this time period, about 1.8 million years ago. Also on the yes side is the presence of four other Homo fossils from the same site that probably lived within a couple of hundred years (or more) of one another. What makes this exciting for many paleoanthropologists is that it provides an idea of the range of anatomical variability present in a single population or deme (a local population which interbred). And there was a lot of variability, especially in cranial shape and facial robusticity (heaviness of features). It is this variability that has caused the stir among paleoanthropologists. For about forty years now, paleoanthropologists have known that that the fossils they attribute to early Homo (roughly 2.4 – 1.5 million years ago) were not all exactly alike. They varied in terms of brain size, facial size and shape, and even body size, though evidence of bones below the head was pretty scarce. Almost all of these early Homo fossils came from different places in East and South Africa, and they covered a geological age span of almost one million years. So interpreting the variability was difficult. Perhaps it represented geographic differences, or different points in an evolutionary continuum. What the Dmanisi fossil #5 suggests, or so the authors argue, is that this variability in early Homo fossils might just have been normal within population variability, and that there was only one species of early Homo, instead of the three or four usually proffered (Homo habilis, Homo rudolfensis, Homo ergaster, Homo erectus). If this little internecine squabble concerning the meaning of variability is your cup of tea then yes, the Dmanisi fossil is very exciting.
But it does not rewrite the basic outline of human evolution. Indeed, it is unlikely to warrant more than a brief mention in an introductory course on human evolution. The evidence still points to Africa as the place where early Homo first evolved out of earlier, smaller brained hominins (increase in brain size is the most important diagnostic feature of the genus Homo), and the time frame still falls between 2.4 and 1.5 million years ago for these earliest members of our genus. And one of them, Homo erectus, became very successful, leaving Africa and expanding geographically all the way to Southeast Asia and eventually Northeast Asia, and west into southern Europe. What we do not yet know is whether the Dmanisi Homo were the first push of this expansion, or whether Homo erectus proper followed soon after.
The ironic thing about the excitement surrounding this description is that arguably the most interesting thing about Dmanisi fossils is not this one (fossil #5), but one reported several years ago. It is an edentulous adult male. Edentulous means “toothless;” this individual had lost all of his teeth, and yet had survived for several years. How? It can only be that members of his social group helped him survive, and that provides fascinating clues about his way of life.