Lone Survivors (5 page)

However, the results strongly supported the Recent African Origin view that people like Günter Bräuer (from Hamburg) and I had been developing from the fossils. Günter was less inclined to view
Homo sapiens
as a newly evolved species, and more inclined to think that hybridization had occurred with people like the Neanderthals, following the dispersal from Africa, but we both welcomed the new mtDNA data. For me, it gave greater confidence that even where the fossil evidence was patchier or more ambiguous, such as the Far East and Australasia, the story of replacement that I had read from the European record probably applied there too.

In 1987 the archaeologist Paul Mellars and I co-organized an international conference in Cambridge where recent fossil and archaeological results were compared with the new DNA data, and the discussions were electric at times, as experts got to grips with the rapidly changing landscape of recent human evolution. A year later, taking the conference discussions and DNA analyses fully on board, I wrote a review of that emerging picture for the journal
Science
, with my Natural History Museum colleague Peter Andrews. We laid out the two contrasting models of Multiregionalism versus Recent African Origin and what would be expected from the fossil, archaeological, and genetic data if either model was an accurate representation of recent human evolution. (I actually prefer to use the term Recent African Origin [RAO], despite the popularity of Out of Africa, because we know from more ancient fossils that there were earlier human dispersals from Africa. Hence some people distinguish them as Out of Africa 1, Out of Africa 2, et cetera, although we don't actually know how many there were—and no doubt there were some “into Africa” events as well!)

Overall, we showed that RAO was best supported, although we recognized that the archaeological record in general and the fossil records of several regions in particular were still not adequate to test the models properly. I was shocked, though, by some of the vitriolic reactions to that paper. Both in the anonymous reviews that some other scientists sent to the journal before publication, and in letters and media comments afterward, scorn was poured on our views and interpretations, a scorn that seemed to extend to personal abuse at times. Relations became strained with a number of scientists, some of whom were people I certainly counted as my friends. Cordiality was eventually restored in most cases, but for a few people, what was seen as an extreme position, in league with the heresy of Mitochondrial Eve, was not easily forgiven or forgotten.

Two of the architects of the Recent African Origin model, Günter Bräuer (left) and Chris Stringer, pictured in the 1980s.

As more fossil and, particularly, genetic data emerged to support a recent African origin, what we can term the classic RAO model was developed by a number of researchers, including me, working separately or in collaboration. By the turn of the millennium, this had become the dominant view. Fleshing it out with the consensus view for earlier human evolution, the classic RAO model argued for an African origin of two human species—
Homo erectus
and
Homo sapiens
—and perhaps also of
Homo heidelbergensis
between them (in my view, though, the derivation of
heidelbergensis
is still unclear). Having evolved from something like the earlier species
Homo habilis
in Africa nearly 2 million years ago (Ma),
Homo erectus
dispersed from Africa about 1.7 Ma, in the event commonly known as Out of Africa 1. The species spread to the tropical and subtropical regions of eastern and southeastern Asia, where it may have lingered on, evolved into other forms, or died out. About 1.5 Ma, African
erectus
developed more advanced stone tools called
handaxes
, but these did not spread far from Africa until they turned up rather suddenly with the descendant species
Homo heidelbergensis
in places like southern Europe, and then in Britain, 500,000 to 600,000 years ago.

So my view was that
H. heidelbergensis
subsequently underwent an evolutionary split around 300,000 to 400,000 years ago: it began to develop into the Neanderthals in western Eurasia, while the line in Africa had evolved into the ancestors of modern humans by about 130,000 years ago. The origin of modern
Homo sapiens
must have been a relatively recent and restricted one in Africa, based on marked similarities between recent humans in both body form and DNA, and it may have been quite rapid, in one small favored area such as East Africa. Some modern humans dispersed to the Middle East (Israel) about 100,000 years ago, and they had perhaps moved on as far as Australia by about 60,000 years. However,
Homo sapiens
did not enter Europe until about 35,000 years ago, following the rapid development of more advanced Later Stone Age tools and complex behaviors by African moderns about 50,000 years ago. Such progress finally allowed the moderns to spread into Europe, where, as Cro-Magnons making Upper Paleolithic tools, they quickly took on and replaced the Neanderthals through their superior technology and adaptations. Bear this narrative in mind, as I will revisit it at various times later in this book.

If RAO is the most accurate model, regional (“racial”) variation only developed during and after the dispersal from Africa, so any seeming continuity of regional features between
Homo erectus
and present counterparts in the same regions outside of Africa must have been as a result of parallel evolution or coincidence, rather than of genes passed down from archaic predecessors, as argued in the Multiregional model. Like that model, RAO argued that
Homo erectus
evolved into new forms of humans in inhabited regions outside of Africa, but in RAO these non-African lineages eventually became extinct, without evolving into modern humans. Some, such as the Neanderthals, must have been replaced by the spread of modern humans into their regions, and hence the RAO model not only is popularly known as Out of Africa but is sometimes also known as the Replacement model.

As RAO gathered support and influence, it increasingly made an impact on the views of people like the American anthropologists Fred Smith and Erik Trinkaus, who believed in continuity outside of Africa but were not classic multiregionalists. Instead, they advanced what has become known as the Assimilation model, which can be seen as a moderate position between the extremes of RAO and what I have dubbed classic Multiregionalism: one where Africa dominated as the source of modern features, but where these were taken up more gradually by people outside of the continent, through a blending of populations. Modern features thus diffused out of Africa rather than being imposed through the invasion and dominance of dispersing moderns, and early moderns outside of Africa could therefore be expected to show features of the “natives” with whom they were mixing. And while the various models of human evolution were adjusting themselves to the post-mtDNA landscape, the genetic work itself was undergoing reevaluations.

I already mentioned the heavy criticisms of the 1987 “Eve” paper, from the point of view of the samples used, the methods of analysis, the rate of evolution, and the strong conclusions drawn. The team involved in the original work acknowledged that there were deficiencies, and, over the next few years, they set out to address the problems in a series of further analyses that served only to reinforce their conclusions, as we shall see in chapter 7. But as we shall also observe, most workers now agree that mtDNA, while very useful, is only one small part of the genetic evidence we need to reconstruct our evolutionary origins.

For the rest of this book, I will mainly be discussing three other human species along with our own:
Homo erectus
,
H. heidelbergensis
, and
H. neanderthalensis
. So how do we recognize distinct human species in the fossil record and our own ancestors? Well, that is not a straightforward question, and specialists will give differing answers. (For example, as I explained earlier, multiregionalists often regard
Homo sapiens
as the only human species on Earth during the last million years, so species like
Homo erectus
and
Homo heidelbergensis
have no real meaning for them.) But for me, there are features in the skeleton that, taken together, can diagnose distinct human species in the past, and that similarly characterize our species today. Because of variations in time and space, these features are rarely absolute, but in combination I think they can distinguish separate evolutionary lines that we can call species, based on their skeletal structure.

For our own species,
Homo sapiens
(modern humans), these features include: a large brain volume; neurocranial globularity (the curvature and doming of the bones of the braincase, and its increased height); in rear view a braincase that is wider at the top and narrower at the base; a higher and more evenly arched temporal bone at the side of the braincase; decreased height of the face and its tucking-in under the braincase; a small and divided brow ridge; a narrow area of bone between the eye sockets; increased projection of the middle of the face and nose; a bony chin on the lower jaw, present even in infants; simplification and shrinkage of tooth crowns; a lightly built tympanic bone (this contains the ear bones); a short pubic ramus that is nearly circular in cross section (this is a bone at the front of our pelvis); no iliac pillar (this is a near-vertical ridge of bone reinforcing the pelvis, above the hip socket); and femora (thighbones) that are oval in cross section and thickened most at the front and back.

In contrast, for
Homo erectus
, the human species that had appeared in Africa and Asia more than 1.5 million years ago, the characteristics included a small average brain volume; a relatively long and low braincase, narrow across the top but broad across the base; a lower and more triangular temporal bone; an angled occipital bone at the back of the skull, with a strong torus (ridge of bone) across it; bony ridges that reinforce the frontal and parietal bones of the braincase; a thick tympanic bone; a strong and continuous supraorbital torus (brow ridge); a strong postorbital constriction (the skull is pinched in behind the brow ridge when viewed from above); a wide area of bone between the eye sockets; a face that juts out from the braincase; a flatter and elongated superior pubic ramus; an iliac pillar; and femora that are rounded and evenly thickened in cross section.

Homo erectus
seems primitive in many respects by the standards of later humans, but it represented a benchmark of change to the human condition in many aspects of its skeleton: a brain size beyond any ape or australopithecine, a human face with projecting nasal bones, small teeth, a humanlike posture for the skull, and a body frame of human rather than apelike proportions. The evolutionary biologists Dennis Bramble and Daniel Lieberman believe that
erectus
had made a fundamental transition to life in the open, first scavenging and then hunting over long distances. We are unique among primates in our capacity for endurance running, which may first have evolved to allow humans to get to carcasses for scavenging ahead of the competition. And people like the San today are able to gradually wear down their prey through persistent pursuit: ungulates, for example, can run much faster than humans over short distances but completely exhaust themselves over long distances, at which point they are easy to dispatch. Features of the
erectus
(and later human) skeleton in body shape, legs, ankles and feet, head balance and stability, and our reliance on sweating to thermoregulate could all be relics of an early adaptation to sustained running, according to Bramble and Lieberman.

H. heidelbergensis
, present in Africa and Europe more than 500,000 years ago, shows combinations of features found in the more primitive
erectus
fossils and those found in the later Neanderthal and modern
sapiens
fossils, as befits a possible intermediate species: a brow ridge like
erectus
, but often filled with extensive sinuses (voids); an occipital bone like that of
erectus
; a wide interorbital breadth like
erectus
; a superior pubic ramus like
erectus
; an iliac pillar like
erectus
; rounder femora like
erectus
; brain volumes that overlap the smaller values of
erectus
and the larger ones of
H. sapiens
and
H. neanderthalensis
; a braincase higher than
erectus
, and parallel-sided in rear view; a face intermediate between
erectus
and later humans in its overall projection from the braincase; a temporal bone more like those of
sapiens
and
neanderthalensis
; a tympanic like Neanderthals and moderns; increased projection of the middle of the face and nose (as in Neanderthals and moderns); and, in some cases, inflated cheekbones that retreat at the sides, like those of Neanderthals.