In the mid-twentieth century, there was general agreement amongst paleoanthropolo-gists that only one hominin species existed at any one time across the Old World and that its members evolved from Australopithecus to H. sapiens, assisted by extensive gene flow, through grades that many would then have termed habiline, erectine, neanderthal and sapient, succeeding one another through time. However, even when such
Multiregional scenarios for human evolution were the vogue, cracks were developing in the fagade. As early as 1960, William Howells (1960:336-9) was disagreeing with what we regard today as the multiregional hypothesis, stating that H. sapiens must have evolved in a region separate from the Neanderthals, expanding from there to interbreed with them and eventually to replace them. Howells did not know where that area was and just referred to it as the 'main area', probably tropical, somewhere in Africa or Asia.
The arguments against multiregionalism were solidified by advances in genetics and fossil discoveries during the late 1980s and 1990s, especially the identification of African Eve in 1987 through mtDNA analysis. These advances gave rise to the specific 'out of Africa' hypothesis for anatomically and behaviorally modern humans that dominates much thinking today This is focused on an expansion from Africa within the past
100,000 years (or thereabouts) that led to the extinction of all previous hominin species across the Old World. Multiregional evolution never really recovered from the shock provided by the mtDNA bombshell. The concept also suffered with the growing realization that some close hominin cousins of Homo undoubtedly became extinct, especially the robust Australopithecines who survived in Africa, alongside species of Homo, down to almost one million years ago (Figure 3.1).
However, was it all as coldhearted and final as it might seem for the archaic pre-sapiens species of Homo, species that must have become extinct across the whole of Eurasia very rapidly if one accepts a 100% out of Africa model for sapiens ancestry? These other hominin species included H. erectus in Java and China, the Neanderthals in western Eurasia, H. floresiensis, the Denisova hominin from the Altai Mountains, and possibly other late-surviving archaic hominins in parts of Africa. The modern genetic record is now suggesting that small levels of interbreeding between such extinct hominin species and our own ancestors may have happened on many occasions. Prominent amongst these are the recently announced low levels of interbreeding in Eurasia between early modern humans on the one hand, and Neanderthals and Denisovans on the other.31
Given this new information, we should perhaps not think of these Late Pleistocene species as always forming closed populations for breeding purposes, as advocated earlier in this chapter in connection with the species concept in hominins in general. We are such a closed species today because all other hominin species are either extinct or assimilated without obviously identifiable survivors. Interestingly, as members of H. sapiens we are all perfectly capable of successful interbreeding, regardless of geographical origin, even though our ancestral diversification in Africa is currently estimated from various molecular clock analyses and the fossil record to have commenced between 100,000 and 300,000 years ago.32 The Neanderthal-sapiens evolutionary bifurcation out of H. heidelbergensis occurred perhaps 600,000 to 800,000 years ago. From such dates, we can begin to understand that complete genetic barriers to successful procreation might have required upwards of a million years to develop. Indeed, Garrigan and Kingan 2007 have noted that two species of baboon are still capable of producing fertile offspring after an estimated genetic separation time of five million years.
All of this makes possibilities for hybridization throughout the whole of the hom-inin fossil record rather large. Extinction by assimilation rather than total extermination becomes an attractive hypothesis for those archaic hominin species that came face to face with modern humans. Sharp confrontation between out of Africa and multiregional models for the emergence of H. sapiens are therefore no longer productive. It is time for a compromise, as long as the compromise recognizes the importance of migration out of Africa as a foundation factor in the rise of modern humans.
The Recognition of Modern Humans in Biology and Archaeology
The concept of modern human has three components - anatomical (skeletal), genetic, and behavioral. The anatomical modernity enshrined in the taxon H. sapiens is defined by Richard Klein (2009a: 623-4) as a mean brain size over 1350 ccs, prominent forehead and chin, a cranium generally globular in shape with its widest point above the ears (rather than close to the ears as in most earlier hominins), and a high degree of facial retraction and gracility Cranial remains with these characteristics have been found in a number of sites in Africa, especially in the east and south, dating radiometrically between 100,000 and 200,000 years ago.
The most significant examples come from the Omo-Kibish and Herto localities in Ethiopia (Figure 3.5). These remains still carry archaic features no longer strongly marked in most modern humans, such as brow ridges and occipital crests at Herto, but they are agreed by most authorities to be directly within the anatomical ancestry of modern H. sapiens. The Omo remains were found with Acheulian tools. Their dates, approaching 200,000 years ago, obviously support an origin for anatomically modern humans in eastern Africa, being considerably older than any similar remains from southern Africa or Eurasia.33 The Herto remains, from two adults and one child, are dated to 160,000 years ago and carry traces of defleshing, for unknown reasons, but not necessarily cannibalistic. Stratigraphically-related deposits in the Herto region contain a late Acheulian industry with a component of prepared cores (Levalloisian technology - see Figure 3.4), transitional to what, in Africa, is generally termed the Middle Stone Age. This was a period of great importance in early modern human affairs, associated in Africa with the appearance of a number of archaeological indicators of an increasingly sentient humanity34
One aspect of H. sapiens biology that supports an origin in a tropical region, such as Ethiopia and East Africa generally, rather than in the more temperate far north or south of Africa, is that all modern humans are relatively free of body hair. This was probably lost to allow more efficient heat loss by sweating in open and hot tropical environments (Ruxton and Wilkinson 2011). Eventually, this allowed modern humans to acquire, through migration and adaptation to differing levels of ultraviolet radiation, the latitudinal variations in skin pigmentation that we regard today as so definitive a marker for the geographical divisions within our species. Our lack of body hair also renders us susceptible to the effects of extreme cold, and this is perhaps why, during the past 50,000 years, carefully prepared clothing of cut and shaped animal skins or woven textiles has been developed in northern latitudes.
The genetic record has been revealing the same picture of an African origin for H. sapiens at regular intervals since 1987, especially for mtDNA and NRY lineages, although the molecular clock dates for the evolution and dispersal of modern humans are currently undergoing a great deal of flux. Human genetic diversity declines with distance from Africa, reflecting passage through a number of small population bottlenecks and leading to loss of some haploid lineages as populations split and moved away from each other.35 Interestingly a similar observation has recently been applied to phonemic diversity in languages, which also diminishes with distance from Africa, a situation that Quentin Atkinson (2011) believes tracks the early dispersals of H. sapiens through language bottlenecks.36 However, as populations became established in these new locations, so those genetic lineages that survived the bottlenecks would have aggrandized themselves very quickly as their carrier populations grew in numbers, thus giving opportunity for new mutations to occur and spread. MtDNA analysis suggests a rapid appearance of new haplogroups as early modern humans spread through southern Asia.37
We must now turn to the third factor listed earlier, behavioral modernity. Richard Klein (2009a: 742, 2009b), focusing mainly on the western Old World, has suggested that archaeological markers of a modern level of human behavior include the following:
1. a substantial increase in the numbers of recognizable artifact types, with new categories such as projectile points, grinding and pounding tools, spear throwers, nets, bone flutes, eyed needles, beads, and pendants;
2. an increase in the range of raw materials utilized, including bone, ivory, shell, clay (sometimes baked), and pigments such as ochre;
3. an appearance, particularly in the Upper Paleolithic of eastern Europe and Russia, of definite dwellings, in some cases incorporating mammoth bones as structural elements;
4. evidence for ritualized activities such as burial and art, the latter on portable objects as well as on cave walls and undoubtedly present by at least 40,000 years ago in Europe;
5. increasing attention to aquatic resources, from both riverine and marine sources;
6. increasing ability to transport raw materials over tens or even hundreds of kilometers;38
7. the ability, using multiple-layered fitted clothing (Gilligan 2010), and doubtless fire, to penetrate the Arctic Circle to as far as the northern coastline of Asia, and from there eventually to move east into the New World.
Some of these behaviors were present in earlier Eurasian cultural settings. Neanderthals, for instance, buried their dead quite frequently, but whether or not they intentionally placed offerings with those burials is more controversial. They also used bone awls in France, perhaps to make clothing, and used mammoth bones to construct windbreaks of some kind (not necessarily closed huts) in Ukraine (Demay et al. 2012). They knew also how to use fire. So, while most categories in the aforementioned list still seem to be restricted to an association with H. sapiens, many archaeologists nowadays argue against assuming an exclusive correlation.39
Figure 3.5 Old World localities associated with biological and cultural remains of Neanderthals and early H. sapiens. Kya = thousands of years ago. Background map by Multimedia Services, ANU, details added by the author.
Beyond the level of material culture represented in the earlier list, other questions arise concerning the origins of complex language and kinship systems. How did they evolve, and are they unique to modern humans? Both are intricately intertwined, two sides of the same coin, since kinship can hardly exist without language. At the beginning of this chapter, I questioned if early hominins really had kinship reckoning as we know it. We do not know the answer, but early H. sapiens certainly had kinship reckoning in some form. Existing hunter-gatherer societies differ from other primate ones in having cohabiting and interacting groupings of nuclear families, recognized affinal ties based on marriage ('in-laws'), and conscious recognition of kin relationships that tie separate communities across very large areas.40 Hunter-gatherers (including our sapiens ancestors) are mobile, and draw marital partners from wide geographical regions. This means that very early H. sapiens societies could probably have extended as cooperating units across larger areas, in both geographical extent and population, than could non-sapiens hominin bands.
What of language, that most remarkable of our combined biological and cultural creations? Human language is an incredible creation within the biological world, and no other creatures even begin to approach us in linguistic complexity. If an ancient hominin group with language ability like ours met another hominin group without such ability, the result in terms of any significant competition is not hard to imagine. The main question is really one of evolutionary tempo. Was the acquisition of human language by our ancestors a punctuated event, or did it happen gradually over hundreds of thousands of years? There has been a great deal of debate on this issue, and genetics and physiology play important roles in our understanding. But the answer, in fact, is not known, even though some Neanderthals, and even H. heidelbergensis
500,000 years ago in the Sima de los Huesos at Atapuerca, might have had speech capabilities very close to ours, to judge from their possession of a hyoid (tongue supporting) bone very like that of modern humans. However, a new reading of the whole genome of a hominin finger bone from Denisova Cave in the Altai Mountains of Siberia, estimated to be 80,000 years old and thus contemporary with Neanderthals, suggests that this archaic human did not have the full expression of the FOXP2 gene that is believed to be associated with the speech capacity of modern humans (Meyer et al. 2012).
I suspect that questions about when human language and kinship appeared during our evolution will never be answered conclusively. However, I find myself in agreement with the widespread view that the rates of both biological and cultural evolution increased dramatically with the appearance of H. sapiens, both inside and outside Africa, thus allowing the out of Africa movement of modern humans to occur with such success. Richard Klein (2009a: 649) favors rapid neural reorganization of the human brain “that launched the fully modern ability to manipulate culture as an adaptive mechanism.” He believes that this occurred amongst an African breeding population of about 10,000 adults, just prior to the modern human crossing (or crossings) into Eurasia. This is a view that at present cannot be easily dismissed, although the question of the date of modern human emergence out of Africa is currently highly contested.
World History
