Separated at Birth?
Like everyone else, I was eager to look at the jaw. I knew the African erectus specimens well, for my husband, Alan Walker, had co-directed the dig at Nariokotome, Kenya, which had yielded the most complete known skeleton of Homo erectus a few years before. (In 1991, as now, some researchers would call the Nariokotome and other early African specimens Homo ergaster to distinguish them from their presumed descendants in Eurasia, the fossils originally dubbed Homo erectus.) Whatever you wanted to call them, the specimens from Dmanisi and Nariokotome needed close comparison. When Gabunia put his fossil next to the cast of the Nariokotome jaw that Alan had brought, there was an almost visible spark of recognition. The two jaws were not just similar; they might have come from twins. Impulsively, Alan gave Gabunia the Nariokotome cast to take home with him, knowing there was none in the Republic of Georgia.
From then on, I was convinced the new jaw was Homo erectus and probably a very old one. The morphology, the date, the fauna were all right. No other Eurasian site had yielded hominids (human ancestors) anywhere near as old as the Dmanisi jaw; most were less than half a million years old. Only in Africa were there hominids dated to more than 1 million years, and the oldest Homo erectus (or ergaster, for those who preferred that term) in Africa was about 2 million years ago. By about 1 million years, Homo erectus had massively expanded its geographic range and was found in Java, somewhat later in China and later still in Europe. What propelled Homo erectus out of Africa into such a stunning dispersal? And why was there a time lag of almost 1 million years between the species' first evolutionary appearance in Africa and its invasion of Eurasia? It was an intriguing mystery.
In 1989, my husband and I had tackled this problem in a paper published in the Journal of Human Evolution. We interpreted Homo erectus's expanded brain size, increased body size and powerful strength relative to those of previous hominids as evidence that Homo erectus had a strikingly different diet from its predecessors. Earlier hominids were largely or exclusively vegetarian; we hypothesized that Homo erectus was the first efficient, regular hunter in human evolution. Only consistent access to very high-quality food would have enabled erectus mothers to bear and raise offspring with such nutritionally expensive characteristics.