Erik Trinkaus has written a very informative review paper on the paleoanthropological record pertaining to the origin of modern humans. According to his view, modern humans originated in the ecological zone of eastern Africa (evidenced by Omo and Herto), made an early exit into southwestern Asia (Qafzeh), and spread around the world, outside this core area, much later. It is interesting that modern dating techniques have placed most Paleolithic skulls after 28,000BP. Moreover, most of these skulls are European in origin; Trinkaus urges researchers to adequately sample more areas of the world.
The overall impression one gets from this paper is that the human paleoanthropological record is extremely limited. Skulls before 28,000BP are few and are separated by long gaps in space and time. Skulls after 28,000BP are mostly European. Trinkaus criticizes molecular biology for its wider confidence intervals and unstated theoretical assumptions, but one wonders whether the situation in the traditional osteological approach is much better, and whether pronouncements on what constitutes archaic vs. modern can be so easily done with such meagree material. For example, the Herto skulls were assigned to a new human subspecies Homo sapiens idaltu, but it was later found that the more "modern" Omo remains were about 50,000 years older. So, there is no clear progression between archaicity to modernity, even in eastern Africa - not to mention that there is a huge gap between these early remains and the multiple (mostly European) skulls dating to post-28,000BP times.
Trinkaus pronounces both the replacement and regional continuity theories dead. Humans are not descended from regional populations of Homo, and they are not descended from a single African population. Rather, he prefers the assimilation model, whereby a population from the east African ecological zone expanded, assimilating to some extent archaic human populations.
Annual Review of Anthropology
First posted online on June 14, 2005
Early Modern Humans
Perceptions of the emergence and spread of modern humans have changed recently through the reanalysis of fossils, an improved geochronological framework, and the discovery of a few specimens. Early modern humans in various portions of the Old World exhibit complex and varying mosaics of archaic, modern, and regional morphological characteristics. On the basis of this pattern, in conjunction with the emerging chronology of the earliest modern humans, the paleontological data indicate an assimilation model for modern human origins, in which the earliest modern humans emerged in eastern Africa, dispersed briefly into southwestern Asia, and then subsequently spread into the remainder of Africa and southern Asia, eventually into higher latitude Eurasia. The earliest modern humans outside of the core area of eastern Africa can be understood only if a variable degree of admixture with regional groups of late archaic humans occurred. Current and expected fossil and molecular data are unlikely to illuminate the degree of assimilation that took place in most regions of the Old World. However, the current chronological and phylogenetic framework provides the basis for ongoing investigation of the nature of this Late Pleistocene transitional period.