Population dispersal

The issue of population dispersal and ultimately population replacement is central to all of the current debates over modern human origins in Europe. To demonstrate that there was a revolution in cultural and behavioural patterns associated with the appearance of anatomically modern anatomy is one thing. To argue that this reflects a dispersal of entirely new populations over the different regions of Europe is an entirely separate and far more contentious issue.

Throughout this century opinions have tended to polarize between those who saw the appearance of anatomically modern populations (i.e. Homo sapiens sapiens) in terms of colonization deriving initially from one specific geographical centre and subsequently dispersing throughout all areas of the world -- the so-called 'Garden of Eden' hypothesis; and those who saw this event as a much more gradual and localized process of more long-term evolutionary development within each region of the world, without any significant dispersal or replacement of populations - the 'regional continuity' or 'multiregional evolution' hypothesis (Spencer 1984; Smith 1991; Stringer & Gamble 1993). A spate of recent publications on this issue shows that opinions remain no less divided now than 20 or even 50 years ago (e.g. Stringer & Andrews 1988; Stringer 1990, 1994; Wolpoff 1989; Thorne & Wolpoff 1992; Wolpoff et al 1994; Wilson et al 1992).

There is little doubt that a number of discoveries over the past 15 years have tended to shift the balance of evidence in favour of the population dispersal hypothesis. Two developments have been especially critical. On the one hand has been the work on genetic finger-printing of present-day human populations in different regions of the world, based on patterns of variation of nuclear and mitochondrial DNA. In particular, research by Allan Wilson, Rebecca Cann, Mark Stoneking and others on the patterns of mitochondrial DNA (known to be inherited exclusively through the female line of descent, and subject to an unusually rapid rate of genetic mutation) points to a surprisingly recent point of origin for present-day world populations, probably reaching back no more than ca 200-300,000 years (Cann et al 1987, 1994; Stoneking & Cann 1989; Wilson & Cann 1992; Stoneking et al 1992). Combined with results of similar studies of nuclear DNA (inherited through both the male and female lineages: Lucotte 1989; Wainscoat et al 1989; Mountain et al 1992) the genetic evidence as a whole points strongly to Africa as the most likely point of origin of these genetically modern populations - although other potential homelands further to the north and east in Asia have occasionally been debated in the literature (cf. Maddison 1991; Templeton 1992). The second crucial development has come from recent advances in absolute dating techniques, which now make it possible to attribute secure relative and absolute ages to several human skeletal remains whose ages had previously been extremely controversial (Aitken et al 1992). Perhaps the most important development has been the recent dating of large samples of anatomically modern skeletal remains from the sites of Mugharet-es-Skhul and Djebel Qafzeh in Israel to around 90-110,000 BP (Bar-Yosef 1992,1994). The clear implication is that human populations that were essentially modern in at least most anatomical respects (Fig. 13.7) had become established in the Middle Eastern region at least 50-60,000 years before their appearance in the more northern regions of Europe and Asia, and must therefore have

Figure 13.7 Skull of anatomically modern form from Djebel Qafzeh, Israel, dated to ca 90-100,000 BP. After Tiller 1989.

Bilfc coexisted with various Neanderthal and other archaic populations of these regions throughout this period (Vandermeersch 1989, 1993a). Combined with the dating to a similar period of a range of essentially anatomically modern hominids at several sites in southern Africa (e.g. Omo, Border cave, Kla-sie's River Mouth) this gives strong support to the 'Out of Africa' model and is much less consistent with the implications of the multi-regional evolution hypothesis (Stringer & Andrews 1988; Stringer 1990, 1994; Bràuer 1989; Howell 1994).

One final development which has a particularly critical bearing on the interpretation of evidence from western Europe is the discovery of human skeletal remains at the site of Saint-Césaire in the Charente-Maritime Department of western France (Fig. 13.8). Although fragmentary, reconstruction of these remains produced a skull now accepted as being of essentially classic Neanderthal type (Leveque & Vandermeersch 1980; Stringer et al. 1984; Vandermeersch 1993b). The importance of this discovery lies in its dating. From a variety of evidence (archaeological associations, stratigraphy, pollen analysis, as well as direct thermolumines-cence measurements on associated burnt flint samples) it is clear that this skull must date from no earlier than 35-38,000 BP (Mercier et al. 1991). As such, the remains can hardly be more than 3000-5000 years older than the earliest well documented specimens of fully 'Cro-Magnon' forms in western Europe, represented for example at Vogelherd in Germany, Les Rois in western France and Cro-Magnon itself (Fig. 13.9) (Gambier 1989, 1993). The argument, quite simply, is that the human population represented by the Saint-Cesaire remains could not have evolved into populations of fully modern skeletal form within the time span available without a massive component of external gene-flow,

Figure 13.8 Left: Late Neanderthal skull from the Châtelperronian levels (ca 35,000 BP) at Saint-Césaire (Charente-Maritime, southwestern France) Right: Anatomically modern skull from the early Aurignacian levels at Vogelherd (Stetten, southern Germany). After Bräuer 1989.

which would have effectively swamped the genetic and anatomical features of the local Neanderthal populations. Even the most ardent proponents of the population continuity hypothesis seem to accept that the characteristics of the Saint-Cesaire skeleton point strongly to a major population influx into these extreme western fringes of Europe (e.g. Smith 1991).

Most of these discoveries have been challenged in various ways by proponents of the multiregional evolution school, at least regarding the specific interpretations drawn from the genetic and skeletal evidence. Wolpoff, Thorne and others, for example, have challenged the chronological interpretations of mitochondrial DNA evidence and argued that by adopting a rather different rate of genetic divergence in DNA patterns one could redate the inferred dispersal of anatomically modern populations from the presumed African homeland to around 900,000 BP, that is close to the generally accepted date for the initial dispersal of Homo erectus populations into northern latitudes in the early Pleistocene (Wolpoff 1989; Thorne & Wolpoff 1992; Wolpoff et al 1994). Wolpoff, Thorne, Smith and others have also contested the interpretation of the skeletal evidence, arguing that many of the supposed dichotomies between anatomically archaic and anatomically modern populations (for example in Africa, the Middle East and indeed parts of Europe) fail to make due allowance for the probable scale of individual anatomical variation within the local populations (e.g. Smith 1991, 1994). They also argue that in certain other regions, such as southeast Asia, Aus-

Kyr BP

Was this article helpful?

0 0

Post a comment