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Friday, 31 August 2007 00:48

Beginning in the early 1990s, a few hominid remains were found, but the most informative specimens are three well-preserved crania, the most recently discovered (in 2001) being almost complete (see photos). These remains (all dated to approximately 1.8 m.y.a.) are important because they are the best preserved hominids of this antiquity found anywhere outside of Africa. Moreover, they show a mixed pattern of characteristics, some quite unexpected.

In some respects the Dmanisi crania are similar to H. erectus (for example, the long, low vault, wide base, and thickening along the sagittal midline). In other characteristics, however, the Dmanisi individuals are different from other hominid finds outside of Africa. In particular, the most complete specimen (No. 2700) has a less robust and thinner browridge, a projecting lower face, and a large upper canine. Thus, at least from the front, this skull is highly reminiscent of the smaller early Homo specimens from East Africa more so than of Homo erectus. Moreover, cranial capacity if this individual is very small (estimated at only 600 cm3 , well within the range of early Homo). In fact, all three Dmanisi crania show small cranial capacities (the other two estimated at 650 and 780 cm3).

Homo erectus from Dmanisi, Republic of Georgia
Photos courtesy of Professor David Lordkipanidze, Deputy Director, Georgian State Museum

A number of stone tools have also been recovered at Dmanisi. The tools are similar to early African implements and are quite different from the ostensibly more advanced technology of the Acheulian (the latter broadly associated with H. erectus in much of the Old World).

From these recent, somewhat startling revelations from Dmanisi several questions can be raised:

    1) Was Homo erectus the first hominid to leave Africa -- or was it an earlier form of Homo?

    2) Did hominids require a large brain and sophisticated stone-tool culture to disperse out of Africa?

    3) Was the large, robust body build of H. erectus a necessary adaptation to disperse initially into Eurasia.

    4) Did, in fact, H. erectus evolve primarily in Eurasia and then migrate back to Africa?

Of course, the Dmanisi discoveries are very new, so any conclusions we draw must be seen as highly tentative. Nevertheless, the recent evidence raises important and exciting possibilities. In regards to Question 1, it now seems likely the first trans-continental hominid migrants were a form of early Homo (similar to the smaller East African species, Homo habilis). At best, and as exemplified at Dmanisi, the first hominids to leave Africa were a very early form of H. erectus, one much more primitive than any of the other specimens from Africa, Asia, or Europe discussed above.

As for question 2, certainly the smaller individuals from Dmanisi did not have a large brain (by H. erectus standards), nor did they have an advanced stone tool culture (possessing tools very similar to the earliest ones from East and South Africa).

Question 3 concerns body size and proportions, but is more speculative than the two above queries. Very little postcranial material has been found thus far at Dmanisi, so we do not know as yet the body structure of the earliest hominids to leave Africa. It is possible, however, that the overall body proportions (as with the face of the smallest Dmanisi cranium) resemble Homo habilis more than they do H. erectus. Thus, these first pioneers to leave Africa may have been, in the words of Phillip Rightmire (of the University of Binghamton and a co-author of the first article announcing the 2001 Dmanisi discovery), ‘little people.” That is, they may have been very different from the big-bodied, long-legged, full-blown H. erectus body plan.

And, lastly, where did the full-blown H. erectus morphology first evolve? For decades it has been widely assumed H. erectus evolved first in Africa and then emigrated to elsewhere in the Old World. Hence, now the teasing possibility exists that H. erectus evolved primarily in Eurasia and (only after attaining its fully characteristic morphology) did it migrate back into Africa (as perhaps the Bouri cranium, dated to 1 m.y.a. suggests?).

by Robert Jurmain, San Jose State University.