Origin of Humankindby Richard Leakey
"“The name Leakey is synonymous with the study of human origins,” wrote The New York Times. The renowned family of paleontologistsLouis Leakey, Mary Leakey, and their son Richard Leakeyhas vastly exp"See more details below
"“The name Leakey is synonymous with the study of human origins,” wrote The New York Times. The renowned family of paleontologistsLouis Leakey, Mary Leakey, and their son Richard Leakeyhas vastly exp"
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The First Humans
Anthropologists 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 centuryand 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:
In each great region of the world, theliving mammals are closely related to the evolved species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee: and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.
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 humansbipedalism, technology, and an enlarged brainevolved in concert. He wrote:
If it be an advantage to man to have his hands and arms free and to stand firmly on his feet, . . . then I can see no reason why it should not have been more advantageous to the progenitors of man to have become more and more erect or bipedal. The hands and arms could hardly have become perfect enough to have manufactured weapons, or to have hurled stones and spears with true aim, as long as they were habitually used for supporting the whole weight of the body . . . or so long as they were especially fitted for climbing trees.
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 daggerlike 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. In 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 Wallacewho also invented the theory of natural selection, independently of Darwinbalked 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 shapethat is, an arch, broadening slightly toward the rear, and not a "U" shape, as in modern apes.
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