Lone Survivors (4 page)

These were the main ideas about the origin of modern humans that I set out to test when I began my studies for a Ph.D. at Bristol University in 1970: the global Multiregional model and its Braceian development, the Early Neanderthal model, the Pre-
sapiens
model (with no place for
erectus
or Neanderthals), and one rather vaguer scheme developed by the anthropologists Bernard Campbell and Joseph Weiner called the Spectrum Hypothesis. This argued that ancient humans had different blends of what would become modern human characteristics, and they contributed in part, and differentially, to the evolution of
Homo sapiens
. So in a sense the Spectrum Hypothesis was multiregional, but some lineages had a much greater contribution to our ancestry than others. A bit of a revolution was under way around 1970, as computing power started to increase and began to influence the biological sciences. Most analyses of human evolution up to 1970 were based on direct observation, and where measurements of a fossil were taken, these were usually compared individually or through an index of just two measurements. However, multivariate programs were becoming available that could look at large numbers of measurements and specimens simultaneously, allowing more sophisticated studies of differences in size and shape. Such analyses were at the center of my studies for a doctorate, and in July 1971 I left the United Kingdom on a trip to museums and research institutes in ten European countries. The aim was to gather as many data as possible on the Neanderthals and their modern-looking successors in Europe, the Cro-Magnons, to see whether the evolutionary pattern was one of continuity or rupture. I only had a modest grant from the Medical Research Council for a four-month trip, and so I drove my old car, sleeping in it, camping, or staying in youth hostels—in Belgium I even spent one night in a shelter for the homeless. I survived many adventures, including several border confrontations and two robberies, but by the end of my 5,000-mile trip I had collected one of the largest data sets of Neanderthal and early modern skull measurements assembled by anyone up to that time.

Chris Stringer on his 1971 research trip around Europe. It's washing day at a campsite in Yugoslavia.

Over the next two years I analyzed this information, adding comparative data on non-European fossils and modern human populations (the latter generously supplied by the American anthropologist William Howells). The measurements were transferred to data cards and fed into a computer the size of several rooms, but which had less processing power than my last mobile phone! Nevertheless, the results were instructive. Neanderthal skulls were no more similar to those of recent Europeans than they were to Africans, Eskimo, or Native Tasmanians, and Cro-Magnon skulls did not neatly slot between the Neanderthals and recent Europeans. Early modern skulls from around the world seemed to cluster with their modern counterparts rather than with any archaic skulls from the same regions. The former results provided no support for a Neanderthal ancestry for the Cro-Magnons, and the latter results contradicted Multiregional and Spectrum expectations. Studying the sequence in Europe before Neanderthal times also gave no support to the Pre-
sapiens
model either, because very early European fossils could not be divided into modern-like and Neanderthal-like; they seemed to show the gradual development of only Neanderthal features through time.

Things were not quite as clear in the Middle East, although there did not seem to be any “intermediate” fossils between Neanderthals and moderns there either. Skulls from Tabun and the Israeli cave of Amud seemed to be basically Neanderthal, while those from Skhul Cave seemed much more modern. But because none of these finds were well dated in the 1970s, I couldn't exclude the possibility that, given enough time, the Israeli Neanderthals could have been transformed into early moderns, in line with the Early Neanderthal model of scientists like Clark Howell. However, a surprising alternative ancestor for the Skhul and Cro-Magnon early moderns did emerge from my results. A skull discovered in 1967 in the Omo Kibish region of Ethiopia, by a team led by Richard Leakey (the son of the famous prehistorians Louis and Mary Leakey), looked very modern in my skull shape analyses, confirming the first studies by the anatomist Michael Day; yet preliminary dating work suggested it could have been as much as 130,000 years old, more ancient than most Neanderthals. And there was an enigmatic North African skull, found in the Moroccan site of Jebel Irhoud in 1961. In skull shape it seemed Neanderthal in some ways, yet its facial shape was non-Neanderthal, partly primitive and partly modern. With an age thought to be only around 40,000 years, it was difficult to fit Jebel Irhoud into any scenario, but it and the Omo skull provided clues that Africa was going to have its own story to tell, when more data came in.

As my work developed through the 1970s and early 1980s, I gravitated increasingly toward what Bill Howells in 1976 had dubbed the Garden of Eden (or Noah's Ark) model. This was named not because Howells was any kind of biblical creationist, but because of the implication that all modern human variation had developed from a single center of origin. A lack of fossils from many parts of the world, together with inadequate dating for many of those we did have, meant that neither Howells nor I could specify where that center of origin might have been, although we thought we could exclude the European and Middle Eastern territories of the Neanderthals. We both believed that the distinctive shared features of modern humans, such as the high rounded skull, small brows, and chin, implied a recent common origin, as otherwise there would have been much greater differentiation over time. And I started to move away from the then widespread idea that fossils as different-looking as Broken Hill, the Neanderthals, and Cro-Magnon should all be classified with us as variants of our species,
Homo sapiens
. Initially I agreed with some other workers in differentiating “anatomically modern
sapiens
” (such as Skhul and Cro-Magnon) from “archaic
sapiens
” forms such as Neanderthals and Broken Hill. But during the 1980s I increasingly favored limiting the
sapiens
term to fossils closely resembling us. Moreover, along with a few other heretics, I started to argue that the Neanderthals should be returned to the status granted them by William King in 1864 as a distinct species,
Homo neanderthalensis
. I also suggested that the Broken Hill skull found in 1921 could be grouped with more primitive European forms (for example, the Heidelberg jaw discovery of 1907) as
Homo heidelbergensis
.

As my views on our origins were developing toward a single-origin model, evidence began to accumulate that Africa was especially important in this story. The Omo Kibish find was joined by material from the sites of Border Cave and Klasies River Mouth Caves in South Africa. Moreover, new dating work hinted that Africa was not the backwater in cultural evolution that most considered it to be. Archaeologists such as Desmond Clark and Peter Beaumont argued that it might instead have been leading the way in the sophistication of its stone tools. By 1980 I was privately convinced that Africa was the main center of our evolution but, because of dating uncertainties, I could not rule out the Far East as also playing a role. It took another four years for me to take a strong “Out of Africa” stance publicly, as various lines of evidence started to fit together in my mind.

However, further confusion was sown by the strong reemergence of Weidenreich's Multiregional views in 1984. These were given a new lease on life by Milford Wolpoff (United States), Alan Thorne (Australia), and Wu Xinzhi (China). They distanced themselves from Coon's views by returning to Weidenreich's emphasis on the importance of gene flow between the geographic lines, considering the continuity in time and space between the various forms of
Homo erectus
and their regional descendants to be so complete that all of them should be classified with modern people as representing only one species:
Homo sapiens
. Thus in this model there was no real “origin” for the modern form of
Homo sapiens
. A feature like the chin might have evolved in a region such as Africa, and spread from there by interbreeding across the human range, followed by selection for it if it was an advantageous characteristic. Another feature such as our high forehead might have developed in, say, China, and then similarly spread from there through interbreeding. Thus modern humans could have inherited their “local” features through continuity with their ancient predecessors, while global characteristics were acquired via a network of interbreeding.

But new developments in genetics research were about to have a huge impact. In 1982 I became aware of research work on a peculiar type of DNA that is found outside the nucleus of cells, in the
mitochondria
. These are little bodies that provide the energy for each cell, bodies that probably originated from a once-separate bacterium, which somehow survived being engulfed by a primitive cell. They then coevolved to confer mutual advantage and developed into the mitochondria that most organisms have throughout their cells. In humans, the DNA of a mother's mitochondria is cloned in her egg when it becomes the first cell of her child, and little or no mitochondrial DNA from the father's sperm seems to be incorporated at fertilization. This means that mitochondrial DNA (mtDNA) essentially tracks evolution through females only (mothers to daughters), since a son's mtDNA will not be passed on to his children. This type of DNA mutates at a much faster rate than normal (nuclear) DNA, as we will discuss in chapter 7, allowing the study of short-term evolution. Early work on human mitochondria seemed promising, showing that our species apparently had low diversity and a recent origin, but the geographic patterns seemed unclear as to where that origin might be. By 1986 I had heard through the grapevine that startling new mtDNA results were on the way to publication, and a year later they appeared in the science journal
Nature
, shaking up arguments about recent human evolution in such a way that things would never be the same again. This seminal publication by Rebecca Cann, Mark Stoneking, and Allan Wilson put modern human origins on the front pages of newspapers, journals, and magazines for the first time.

Milford Wolpoff, an architect of Multiregionalism, with a
Homo erectus
skull from Java.

About 150 types of mtDNA from around the world were investigated, and their variation was determined. Then a computer program was used to connect all the present-day types in an evolutionary tree, with the most economical pattern of evolutionary change (mutations), reconstructing hypothetical ancestors for the living types. In turn, the program connected those ancestors to each other, until a single hypothetical ancestor for all the modern types was created. The distribution of the ancestors implied that the single common ancestor must have lived in Africa, and the number of mutations that had accumulated from the time of the common ancestor suggested that this evolutionary process had taken about 200,000 years. This, then, was the birth of the now-famous Mitochondrial Eve, or “lucky mother,” since the common mitochondrial ancestor must necessarily have been a female. These results seemed to provide strong evidence for a Recent African Origin view for modern humans, since the research suggested that a relatively recent expansion from Africa had occurred, replacing any ancient populations living elsewhere, along with their mtDNA lineages. However, the work was soon heavily criticized. It was shown that the kind of computer program used could actually produce many thousands of trees which were all more or less as economical as the published one, and not all of these alternative trees were rooted in Africa. Moreover, other researchers criticized the calibration of the time when Mitochondrial Eve lived, while yet others questioned the constitution of the modern samples analyzed (for example, many of the “African” samples were actually from African Americans). As a result, multiregionalists were, for a while at least, able to reject these mtDNA results as irrelevant or misleading, arguing that fossil evidence (and their interpretation of it) remained the only valid approach to reconstructing recent human evolution.