New Finds of Early Homo sapiens from Ethiopia

FOSSIL: Homo sapiens idaltu, BOU-VP-16/1, adult
VIEW: Lateral +
SITE & LOCATION: Upper Herto Member, Bouri peninsula, Middle Awash, Ethiopia
FOSSIL CREDIT: Housed in National Museum of Ethiopia, Addis Ababa
COPYRIGHT PROTECTION NOTICE: Photo (c) 2001 David L. Brill \ Brill Atlanta

The origin and dispersal of modern humans (Homo sapiens sapiens) has for years been the most hotly debated topic concerning the latter stages of hominid evolution. Various theories have been proposed, and evidence has been gathered from a variety of sources. Since the 1980s accumulating data detailing the genetic patterning of contemporary humans have increasingly supported a view that the earliest modern people first arose in Africa and dispersed to other regions sometime after 200,000 years ago.

Thus, fossil hominids from Africa in the time range between 200,000 and 100,000 y.a. would be crucial to help substantiate this “Out of Africa” (in the text referred to as “Complete Replacement”) hypothesis. Frustratingly, however, such fossils from the African continent have been hard to come by. There are a few crania from South Africa (e.g., Florisbad) and East Africa (e.g., Omo), but none are securely dated. In other cases (e.g., Klasies River Mouth), the fossil remains are fragmentary.

The announcement in June 2003 of well-preserved and well-dated Homo sapiens fossils from Ethiopia has now gone a long way to filling these gaps in the later Pleistocene African fossil record. Tim While (of the University of California, Berkeley) and colleagues have been working for over a decade in the Middle Awash area of Ethiopia, discovering there a remarkable array of early fossil hominids (Ardipithecus and Australopithecus garhi) as well as somewhat later forms (Homo erectus) (see the text for further discussion). From this same area in the Middle Awash (in the Herto Member of the Bouri Formation) highly significant new discoveries came to light in 1997. For simplicity sake, these new hominids are referred to as the Herto remains.

These exciting new Herto fossils include a mostly complete adult cranium, a fairly complete (but heavily reconstructed) child’s cranium, and another adult incomplete cranium (plus a few other cranial fragments). Following lengthy reconstruction and detailed comparative studies, Professor White and colleagues were prepared to announce their findings in 2003.

FOSSIL: Homo sapiens idaltu, BOU-VP-16/1, adult VIEW: Frontal SITE & LOCATION: Upper Herto Member, Bouri peninsula, Middle Awash, Ethiopia FOSSIL CREDIT: Housed in National Museum of Ethiopia, Addis Ababa COPYRIGHT PROTECTION NOTICE: Photo (c) 2001 David L. Brill \ Brill Atlanta

What they found is quite remarkable and has made an instant impression throughout paleoanthropology (and was reported widely in the popular press as well). Firstly, well-controlled radiometric dating (⁴⁰Ar/³⁹Ar) securely places the remains at between 160,000-154,000 years ago -- making these the best-dated hominid fossils from this time period from anywhere in the world. Secondly, the preservation and morphology of the remains leaves little doubt as to their relationship to modern humans. The mostly complete adult cranium (see photo) is quite dramatic; it is very large, with an extremely long cranial vault. The cranial capacity is 1450 cm³, well within the range of contemporary H. sapiens populations. The skull is also in some respects heaviliy built – with a large arching brow ridge in front and a large projecting occipital protuberance in back. Nevertheless, the face is non-projecting, in stark contrast to Eurasian Neandertals.

The overall impression is that this individual (as well as the subadult, a child aged 6-7 years, and the incomplete adult cranium) are all clearly Homo sapiens. Professor White and his team performed comprehensive statistical comparisons of these fossils with other early H. sapiens remains as well as a large series (N>3000 crania) from modern populations. The conclusion was, while not identical to modern people, the Herto fossils are “near-modern.” In order to distinguish these individuals from fully modern humans (H. sapiens sapiens), the researchers have placed them in a newly defined subspecies: Homo sapiens idaltu (Idaltu, from the Afar language, meaning “elder”).

Further analysis has shown that the morphological patterning of the crania does not specifically match that of any contemporary group of modern humans. What can we then conclude? Firstly, an African origin of modern humans is strongly supported by these new finds. The Herto fossils are of the right age and come from the right place. Moreover, they look much like we might have predicted. These individuals, so long buried in the earth of East Africa tell us, their likely descendants, vital information about our origins. Firstly, our roots as a species do trace back to Africa. Secondly, the dispersal out of Africa (to other areas) occurred after 200,000 y.a., and most likely, after 150,000 y.a.

Sources:

White, Tim, Berhane Asfaw, David DeGusta, et al. 2003 “Pleistocene Homo sapiens from Middle Awash, Ethiopia.” Nature, 433:742-747.

Clark, J. Desmond, Yonas Beyene, Giday WoldeGabriel, et al. 2003 “Stratigraphic, Chronological and Behavioural Contexts of Pleistocene Homo sapiens from Middle Awash, Ethiopia.” Nature, 423:747-752.