The Dmanisi site, tucked into the Anti-Caucasus mountains at about 41 degrees north latitude — similar to present-day New York and Beijing — would have presented a particular challenge for an African species.
“At the higher latitudes, you’re confronting seasonality for the first time,” Tappen says. “They were experiencing winter. No other primate lives where there’s no fruit in winter. There may be a dry season, but there’s not a cold winter like these individuals in Dmanisi were experiencing.”
Tappen believes the hominids, whose brains she describes as “the size of a bocce ball,” survived by adapting to a more meat-centric diet and by eating things like tree bark.
But what puzzles some researchers even more about the Dmanisi hominids showing up more than a thousand miles north of Africa, much earlier in the fossil record than expected, is that they made it to the mountain valley without any advanced technology.
Out of Africa Early
“It would seem that, in the earliest dispersal of humans, some kind of technology would give you an edge. If you don’t have hand axes, maybe you have fire,” says Michael Chazan, an archaeologist at the University of Toronto. “But there is no evidence of either at Dmanisi.”
Chazan is not part of the Dmanisi team, but he has reviewed evidence of the technologies used by hominids there. He says few stone tools have been found at the site compared with other early hominid occupations, such as Ubeidiya in Israel. Intriguingly, the tools at Dmanisi were Oldowan style, also known as flake and core: It’s the simplest stone tool technology, first seen in Africa 2.5 million years ago. In contrast, hominids living in Africa at about the same time as the Dmanisi population were making much more advanced tools, such as hand axes.
The finds at Dmanisi hint that the first humans to leave Africa were not the larger-brained, hand ax-toting, potentially fire-wielding H. erectus. Rather, they were a much more primitive hominid population, possibly Homo habilis, whose members lived in, or at least transited, Dmanisi much earlier than what our accepted chronology of human evolution indicates. It’s possible that the current view on when humans first left Africa is wrong, but if those first pioneers traveled without the easily recognizable advanced tools of H. erectus, it’s also possible we may never find proof.
Says Chazan: “The problem that keeps you awake, if you think about these things, is that if there was a dispersal event 2 million years ago, before H. erectus
, would we see it? If they were using stone tools made of local materials, would we even pick it up? Are we building our models based on things we can’t see?”
Dmanisi team member Tappen agrees the site’s fossils are challenging our current understanding of human evolution — but she’s not losing sleep over it.
“As archaeologists, we go with what we have. We make hypotheses and try to test them, and then you dig up something new and go ‘oops.’ And you have to make up a new hypothesis,” says Tappen.
“The Dmanisi individuals are not too different from H. habilis
. We should find them dispersing out of Africa 2.5 million years ago,” she explains. “We don’t have that evidence yet, but we have to expect it’s out there.”
If there were an earlier hominid exodus from Africa 2 million years ago or longer, researchers don’t expect to find the proof at Dmanisi. All the hominid fossils found so far have been between two layers of volcanic rock from regional eruptions conclusively dated between 1.76 million and 1.85 million years ago.
Rewriting the Family Tree
Archaeologists began digging at Dmanisi in the 1930s, interested in the site’s ruined medieval fortress. While excavating the fortress cellars in the 1980s, researchers began finding the teeth and bones of extinct animals from the early Pleistocene — the first clue to the site’s prehistoric significance.
Since the first hominid fossil was found in 1991, however, the uniqueness of the site itself has been overshadowed by the strange appearance of its early humans. Their short stature and small braincase suggest H. habilis
, which first appeared about 2.3 million years ago in Africa. But H. habilis
never left Africa, according to the current fossil record. And other characteristics of the Dmanisi hominids, such as their more modern limb-to-body proportions, don’t match up with H. habilis
at all but do fit with H. erectus
, which evolved in Africa about 1.9 million years ago. H. erectus
eventually spread as far as China and Indonesia, but not until much later in the fossil record than the Dmanisi finds.