The Origin of Humankind (2 page)

I have had the good fortune to collaborate with many fine colleagues throughout more than two decades of anthropological work, for which I am grateful. To two of them—Kamoya Kimeu and Alan Walker—I should like to extend special thanks. My wife, Meave, has been a colleague and friend of the most extraordinary kind, especially in the most difficult times.

A
nthropologists have long been enthralled by the special qualities of
Homo sapiens
, such as language, high technological skills, and the ability to make ethical judgments. But one of the most significant shifts in anthropology in recent years has been the recognition that despite these qualities, our connection with the African apes is extremely close indeed. How did this important intellectual shift come about? In this chapter I shall discuss how Charles Darwin’s ideas about the special nature of the earliest human species influenced anthropologists for more than a century—and how new research has revealed our evolutionary intimacy with African apes and demands our acceptance of a very different view of our place in nature.

In 1859, in his
Origin of Species
, Darwin carefully avoided extrapolating the implications of evolution to humans. A guarded sentence was added in later editions: “Light will be thrown on the origin of man and his history.” He elaborated on this short sentence in a subsequent book,
The Descent of Man
, published in 1871. Addressing what was still a sensitive subject, he effectively erected two pillars in the theoretical structure of anthropology. The first had to do with where humans first evolved (few believed him initially, but he was correct), and the second concerned the manner or form of that evolution. Darwin’s version of the manner of our evolution dominated the science of anthropology up until a few years ago, and it turned out to be wrong.

The cradle of humankind, said Darwin, was Africa. His reasoning was simple:

We have to remember that when Darwin wrote these words no early human fossils had been found anywhere; his conclusion was based entirely on theory. In Darwin’s time, the only known human fossils were of Neanderthals, from Europe, and these represent a relatively late stage in the human career.

Anthropologists disliked Darwin’s suggestion intensely, not least because tropical Africa was regarded with colonial disdain: the Dark Continent was not viewed as a fit place for the origin of so noble a creature as
Homo sapiens
. When additional human fossils began to be discovered in Europe and in Asia at the turn of the century, yet more scorn was heaped on the idea of an African origin. This attitude prevailed for decades. In 1931, when my father told his intellectual mentors at Cambridge University that he planned to search for human origins in East Africa, he came under great pressure to concentrate his attention on Asia instead. Louis Leakey’s conviction was based partly on Darwin’s argument and partly, no doubt, on the fact that he was born and raised in Kenya. He ignored the advice of the Cambridge scholars and went on to establish East Africa as a vital region in the history of our early evolution. The vehemence of anthropologists’ anti-Africa sentiment now seems quaint to us, given the vast numbers of early human fossils that have been recovered in that continent in recent years. The episode is also a reminder that scientists are often guided as much by emotion as by reason.

Darwin’s second major conclusion in
The Descent of Man
was that the important distinguishing features of humans—bipedalism, technology, and an enlarged brain—evolved in concert. He wrote:

Here, Darwin was arguing that the evolution of our unusual mode of locomotion was directly linked to the manufacture of stone weapons. He went further and linked these evolutionary changes to the origin of the canine teeth in humans, which are unusually small compared to the dagger-like canines of apes. “The early forebears of man were ... probably furnished with great canine teeth,” he wrote in
The Descent of Man;
“but as they gradually acquired the habit of using stones, clubs, or other weapons for fighting with their enemies or their rivals, they would use their jaws and teeth less and less. La this case, the jaws, together with the teeth, would become reduced in size.”

These weapon-wielding, bipedal creatures developed a more intense social interaction, which demanded more intellect, argued Darwin. And the more intelligent our ancestors became, the greater was their technological and social sophistication, which in turn demanded an ever-larger intellect. And so on, as the evolution of each feature fed on the others. This hypothesis of linked evolution was a very clear scenario of human origins, and it became central to the development of the science of anthropology.

According to this scenario, the original human species was more than merely a bipedal ape: it already possessed some features we value in
Homo sapiens
. The image was so powerful and plausible that anthropologists were able to weave persuasive hypotheses around it for a very long time. But the scenario went beyond science: If the evolutionary differentiation of humans from apes was both abrupt and ancient, a considerable distance was inserted between us and the rest of nature. For those with a conviction that
Homo sapiens
is a fundamentally different kind of creature, this viewpoint offered comfort.

Such a conviction was common among scientists in Darwin’s time, and well into this century, too. For instance, the nineteenth-century English naturalist Alfred Russel Wallace—who also invented the theory of natural selection, independently of Darwin—balked at applying the theory to those aspects of humanity we most value. He considered humans too intelligent, too refined, too sophisticated to have been the product of mere natural selection. Primitive hunter-gatherers would have had no biological need for these qualities, he reasoned, and so they could not have arisen by natural selection. Supernatural intervention, he felt, must have occurred to make humans so special. Wallace’s lack of conviction in the power of natural selection greatly upset Darwin.

The Scottish paleontologist Robert Broom, whose pioneering work in South Africa in the 1930s and 1940s helped establish Africa as the cradle of mankind, also expressed strong views on human distinctiveness. He believed that
Homo sapiens
was the ultimate product of evolution and that the rest of nature had been shaped for its comfort. Like Wallace, Broom looked to supernatural forces in the origin of our species.

Scientists such as Wallace and Broom were struggling with conflicting forces, one intellectual, the other emotional. They accepted the fact that
Homo sapiens
derived ultimately from nature through the process of evolution, but their belief in the essential spirituality, or transcendent essence, of humanity led them to construct explanations for evolution which maintained human distinctiveness. The evolutionary “package” embodied in Darwin’s 1871 description of human origins offered such a rationalization. Although Darwin did not invoke supernatural intervention, his evolutionary scenario made humans distinct from mere apes right from the beginning.

Darwin’s argument remained influential until a little more than a decade ago, and was effectively responsible for a major dispute over when humans first appeared. I will describe the incident briefly, because it illustrates the seductiveness of Darwin’s linked-evolution hypothesis. It also marks the end of its sway over anthropological thinking.

In 1961, Elwyn Simons, then at Yale University, published a landmark scientific paper in which he announced that a small apelike creature named
Ramapithecus
was the first known hominid species. The only fossil remains of
Ramapithecus
known at the time were parts of an upper jaw that had been found by a young Yale researcher, G. Edward Lewis, in India in 1932. Simons saw that the cheek teeth (the premolars and molars) were somewhat humanlike, in that they were flat rather than pointed, as ape teeth are. And he saw that the canines were shorter and blunter than those of apes. Simons also asserted that the reconstruction of the incomplete upper jaw would show it to be humanlike in shape—that is, an arch, broadening slightly toward the rear, and not a “U” shape, as in modern apes.

At this time, David Pilbeam, a British anthropologist from Cambridge University, joined Simons at Yale, and together they described these supposedly humanlike anatomical features of the
Ramapithecus
jaw. They went further than anatomy, however, and suggested, on the strength of the jaw fragments alone, that
Ramapithecus
walked upright on two feet, hunted, and lived in a complex social environment. Their reasoning was like Darwin’s: the presence of one putative hominid feature (tooth shape) implied the existence of the rest. Thus, what was thought to be the very first hominid species came to be viewed as a cultural animal—that is, as a primitive version of modern humans rather than as an acultural ape.

The sediments from which the original
Ramapithecus
fossils were recovered were ancient, as were those yielding subsequent similiar discoveries in Asia and Africa. Simons and Pilbeam therefore concluded that the first humans appeared at least 15 million years ago, and possibly 30 million years ago, and this view was accepted by the vast majority of anthropologists. Moreover, the belief in so ancient an origin placed a comforting distance between humans and the rest of nature, which many welcomed.

In the late 1960s, two biochemists at the University of California, Berkeley, Allan Wilson and Vincent Sarich, came to a very different conclusion about when the first human species evolved. Instead of working with fossils, they compared the structure of certain blood proteins from living humans and African apes. Their aim was to determine the degree of structural difference between human and ape proteins—a difference that should increase at a calculable rate with time, as a result of mutation. The longer humans and apes had been separate species, the greater the number of mutations that would have accumulated. Wilson and Sarich calculated the mutation rate and were therefore able to use their blood-protein data as a molecular clock.

According to the clock, the first human species evolved only about 5 million years ago, a finding that was dramatically at variance with the 15 to 30 million years of prevailing anthropological theory. Wilson and Sarich’s data also indicated that the blood proteins of humans, chimpanzees, and gorillas are equally different from each other. In other words, some kind of evolutionary event 5 million years ago caused a common ancestor to split in three directions simultaneously—a split that led to the evolution not only of modern humans but of modern chimpanzees and modern gorillas. This, too, was contrary to what most anthropologists believed. According to conventional wisdom, chimpanzees and gorillas are each other’s closest relatives, with humans standing a great distance apart. If the interpretation of the molecular data was valid, then anthropologists would have to accept a much closer biological relationship between humans and apes than most believed.

An almighty dispute erupted, with anthropologists and biochemists criticizing each other’s professional techniques in the strongest of language. Wilson and Sarich’s conclusion was criticized on the ground, among others, that their molecular clock was erratic and therefore could not be relied upon to give an accurate time for past evolutionary events. Wilson and Sarich, for their part, argued that anthropologists placed too much interpretive weight on small, fragmentary anatomical features, and were thus led to invalid conclusions. I sided with the anthropological community at the time, believing Wilson and Sarich to be incorrect.

The debate raged for more than a decade, during which time more and more molecular evidence was produced—by Wilson and Sarich and also independently by other researchers. The great majority of these new data supported Wilson and Sarich’s original contention. The weight of this evidence began to shift anthropological opinion, but the change was slow. Finally, in the early 1980s, discoveries of much more complete specimens of
Ramapithecus-like
fossils, by Pilbeam and his team in Pakistan and by Peter Andrews, of London’s Natural History Museum, and his colleagues in Turkey, settled the issue (see
figure 1.1
).

The original
Ramapithecus
fossils are indeed humanlike in some ways, but the species was not human. The task of inferring an evolutionary link based on extremely fragmentary evidence is more difficult than most people realize, and there are many traps for the unwary. Simons and Pilbeam had been ensnared in one of those traps: anatomical similarity does not unequivocally imply evolutionary relatedness. The more complete specimens from Pakistan and Turkey revealed that the putative humanlike features were superficial. The jaw of
Ramapithecus
was V-shaped, not an arch; this and other features indicated that it was a species of primitive ape (the jaw of modern apes is U-shaped).
Ramapithecus
had lived a life in the trees, like its later relative the orangutan, and was not a bipedal ape, still less a primitive hunter-gatherer. Even diehard
Rama-pithecus-dLS-hommid
anthropologists were persuaded by the new evidence that they had been wrong and Wilson and Sarich had been right: the first species of bipedal ape, the founding member of the human family, had evolved relatively recently and not in the deep past.