It has only been recently that anthropologists have realised that their best friends are volcanoes. The ash falling from a series of eruptions can produce sequences of fossils nearly as good as those that are normally formed by silt in the sea, and their dates can be accurately measured. Skeletons preserved in this way in the Great Rift Valley of Africa have revolutionised knowledge of man’s ancestry. The first were found by the Leakey family at Olduvai in Tanzania. Expeditions were then undertaken by teams from various countries to sites further north, around Lake Turkana in Kenya, in the Omo Valley, and at Hadar in the Afar triangle in Ethiopia.
These two books describe the results of recent excavations in which the authors have been major participants. Richard Leakey is, of course, the son of a famous father and mother. Of his many discoveries perhaps the most important is the skull cautiously named only by its museum number as KNMER 1470. Until recently it was believed to be the oldest known member of the genus Homo, living 1.8 million years ago. And then along comes Donald Johanson, a young American, finding, near Hadar in Ethiopia, a whole set of hominid fossils dating back nearly twice as far, to 3.5 million years. But the work of the two groups has been by no means separate. Johanson’s chief collaborator, Tim White, was earlier engaged with Mary Leakey on excavation of footprints made by still earlier hominids 3.75 million years ago at Laetoli in Tanzania. Differences arose, however, especially over the interpretation of the fossils from Afar. As so often before, questions of naming have been involved. Those who discover interesting specimens cannot resist the temptation to have a new name attached to their fossil. In this case, Johanson and White decided that all of the Afar bones belonged to a new species, Australopithecus afarensis. But oddly they nominate as the type specimen, not one of the bones they had found, but a similar jaw from Mary Leakey’s collection made 1000 miles away at Laetoli. This has upset many people including Mrs Leakey and her son. So once again in anthropology a quarrel over names is interfering with discussion of the facts.
Johanson’s book contains much description of his finds, but it is given in a style that many will find unattractive. Indeed, it is not clear whether the book is written by Johanson at all. According to the title page, the work is attributed to ‘Donald C. Johanson and Maitland A. Edey’. The latter is ‘a former editor of Life Magazine and Time Life books’. But we hear no more of him, in the Preface or elsewhere. The whole text reads in the first person singular – Johanson. Yet if the voice is the voice of a scientist, the clothes are the clothes of Time-Life. It does not encourage one to trust the historical summary when we are told that ‘Darwin lurked in his home like a timid and anxious turtle.’ If this is the treatment given to the past, how can we be sure of the authenticity of the many verbatim accounts of discussions between Johanson and White as to the naming of fossils.
The descriptions of the expeditions and finds in war-troubled Ethiopia are dramatic, and Mr Edey has written them up well. If you liked Life, this book is for you. But there is an absurd overemphasis on the importance of these discoveries. At several points it is hinted that they may be compared to the analysis of DNA. These are indeed the oldest fairly complete near-human remains, and Johanson and his colleagues are to be congratulated on finding them. They have worked hard in giving descriptions. But these bones do not reveal any new scientific principle, nor do they fundamentally alter our attitude to our origins. Unfortunately physical anthropologists are not in a position to produce ‘hard science’, like molecular biologists: perhaps they never will be.
Richard Leakey’s book costs exactly the same as Johanson’s but is worth many times more. His 256 pages cover far more than the 409 of the other authors’, and in very much better style. The production is excellent, and there are many beautiful and instructive colour photographs. Leakey deals with the history of the subject briefly, and his few words are to the point. He gives a careful and modest description of his family’s findings and of his own. There is a good colour photograph of Johanson, and a generous tribute to him for finding the ‘absolutely fascinating’ Hadar hominids. Leakey then describes Johanson and White’s interpretation of them as a new species and states his disagreement.
Leakey believes strongly that the study of anthropology can bring great benefits in ‘helping us to avoid a frightening future’. It can teach us the ‘unity of mankind ... regardless of creed or culture’. He discusses how proper consideration of the evidence shows that ‘the popular notion of the “killer ape” is one of the most dangerous and destructive ideas that mankind has ever had.’ To give the evidence, he carries the human story far beyond the Olduvai Gorge and through the entire later course of human history: his last picture is of Hiroshima. The evidence about the times of Palaeolithic and Neolithic man and the Agricultural revolution and beyond is much too complicated to summarise fully, but Leakey manages to cover a great part of it.
Perhaps the most interesting general conclusions to be drawn are about the increasing speed of evolution. The earliest evidence of undoubted hominids is the footprints from Laetoli. These were made by three individuals apparently walking calmly while the nearby volcano Sadiman poured out ash, which quickly filled their footmarks and then solidified. One person was walking ‘Wenceslas-like’ in the steps of the one in front, and a smaller individual, presumably a child, walked by their side keeping in step. Obviously these were not the first creatures to walk on their hind legs, and there has been much speculation as to when and why the habit began.
The fossils from Afar include the nearly complete skeleton Lucy and the bones of at least 13 individuals, the ‘first family’, who seem to have died together. These bones confirm that 3.5 million years ago there were hominids with feet quite like ours, though for some reason a little curved. Perhaps these early hominids used them to climb trees. They were only about four foot tall and had brains of ape size. This with other characters is the reason for saying that they are not yet humans – not members of the genus Homo, but to be assigned to the genus Australopithecus and a new species afarensis. Johanson believes that this was the stock that later gave rise both to true man, Homo, and to the two or three other species of Australopithecus, with brains only a little larger, which lived in various parts of Africa up to about one million years ago. Leakey prefers to remain agnostic as to the earlier origin of Homo. He believes that his skull KNMER 1470 is the earliest properly to be referred to our genus – not to Homo sapiens but to the species named by his father Homo habilis. The brain of this type is larger than anything known before, but still only about half the size of modern man’s.
Skulls with still larger brains begin to appear from about one and a half million years ago, not only in Africa, but in many parts of the world – for instance, Java and Peking. These are also not quite human in shape or size, and they are put into another species, Homo erectus. The earliest of them had brains little larger than Homo habilis, but later ones were two-thirds the size of modern man, a few even more. The earliest specimens that can be put in our own species, Homo sapiens, come from less than a quarter of a million years ago, and even they include Neanderthal man, still not quite like skulls of today. Truly modern human remains only appear from deposits later than 40,000 years ago.
So we have now quite a good series of specimens with brains of increasing size – but were they a continuous series, each evolving gradually from the one before? The conventional Darwinian belief that evolution has been continuous has recently been challenged by the theory of punctuated equilibria put forward by the Harvard biologists Gould and Eldredge. This is a new version of the view held for many years by the American geneticist Sewall Wright. He holds that new species arise from favourable changes in small isolated communities, perhaps occurring under special conditions in a small number of generations. This could possibly have happened with our ancestors. Small groups, perhaps isolated by Ice Age conditions, might quickly have developed such human features as long childhood and the elements of language. Such a group may have survived where others did not.
In its extreme form, this theory almost takes us back to the Garden of Eden origin for man, if not quite to a single Adam. There is certainly evidence that some new species have arisen quite suddenly. For instance, Dr Greenwood of the British Museum has shown that five new species of fish have been formed in Lake Nabugabob since its separation from Lake Victoria less than 5000 years ago. As with so many other evolutionary questions, this is partly a matter of deciding what is a new species. In studying a series of ancestors and descendants we cannot know whether the later ones could have bred with the earlier. So the acid test of infertility between groups is impossible, and in that sense the geologist has no way to define his species.
Moreover, in asking whether there have been sudden jumps in evolution we have to decide how big a change is a ‘jump’ and how fast is ‘sudden’. There will never be a sequence of fossil skulls sufficiently complete to show all the stages of human evolution. But with recent discoveries we already have evidence that there were a number of steps in the change from ape to man. Specimens with brains of several intermediate sizes have been found. They are fewer than would be wished but as more and more come to light they suggest a gradual change over the last three million years. Probably the increase has been faster during the last million. But these are very long times and it is difficult to see how we can ever have evidence as to whether there were sudden ‘jumps’, whatever that may mean.
Evolutionary ‘advance’ consists in finding new ways of life. The particularly human way is to live socially, passing information from person to person by language. This is really an entirely new form of biological inheritance – the obtaining of information as to how to live from many individuals and not only by genetic inheritance from two parents. It has already revolutionised, not only man himself, but the whole world. And it is continuing to do so at an ever-increasing rate. So presumably the ‘jump’ that made Man was the discovery of language: but how, when and why did it begin? Probably its proper use requires a long childhood, for instruction, and social behaviour to make use of the information. These could have depended on changes of hormones. Were they associated with new types of brain that allowed speech? Leakey and Johanson both touch on these questions, but we do not know the answers.
Sudden changes in climate might have been a factor influencing change. Neither of our authors discusses fully the recent evidence that during the Ice Ages there were sometimes very rapid changes. The ice of the Arctic retains certain chemical features that tell of the conditions when it was formed long ago. In one period, about 90,000 years ago, the weather became rapidly colder, going in less than 100 years from conditions like those of today to fully glacial. Other evidence from fossils shows that this event, however caused, was world-wide. Such a change would have a tremendous effect on human life today. It could have wiped out many of the early members of our species and left only a few intelligent, cooperative and resourceful groups.
But these are only speculations. Whether or not there were sudden jumps, the evidence is clear that some early human types continued for immense periods. This, of course, is a feature which the theory of punctuated equilibria would lead us to expect. Homo erectus lived for a million years, from at least one and a half to half a million years ago, with little structural change. Their brains probably became larger during this time, and of this we should be able to collect more evidence, since fossils of this type have been found in many parts of the world. Such details will not be so spectacular as finding ‘Lucy’ or ‘the first family’, but might be more useful.
The history of Homo erectus is particularly interesting because they were the first undoubted fabricators of implements, which were as conservative in manufacture as they were in structure. It is not known who made the very earliest crudely chipped ‘Oldowan’ tools of two million years ago. Homo erectus skulls, throughout their long history, are found associated with the rather better ‘hand-axes’ known as Acheulian. As Leakey puts it, ‘these introduce an element of symmetry and sense of purpose that previously was absent.’ The making of them suggests a capacity for ordered thought and instruction (though it by no means proves it). In any case, the techniques remained almost unchanged for a million years. For this immense period, these people continued to flake their hand-axes in almost exactly the same way. But there were gradual changes towards the end.
It is not known whether Homo erectus people were the ancestors of Homo sapiens: we badly need more fossil evidence for the long period from a million to 100,000 years ago. The archaeologists have evidence of new and more economical flaking techniques only in the Mousterian period, beginning less than 200,000 years ago. Changes in technique continued slowly throughout the later Palaeolithic period, but until 40,000 years ago essentially the same tool kit of a few types of axe and scraper was in use. It was only after this that finer and more varied instruments were made, such as fish hooks, arrows, daggers and needles. Even so, we have to deal with change over periods of tens of thousands of years.
The picture that emerges is of intense conservatism, but a very slowly accelerating pace of change. This surely is a major lesson to be learned from prehistory. Change has been proceeding at a continually increasing rate. And it still is. The biological reason for this acceleration is that the genus Homo has invented and increasingly perfected an entirely new method of obtaining and using information about the world. The essence of information is order: it is the opposite of entropy or chaos. By the use of information and intelligence, enormous numbers of humans have been created. Let us rejoice and be proud of our success and not be ashamed of ourselves as too many. What we should be ashamed of is that we do not use our intelligence to distribute resources properly and provide adequately for these multitudes. Richard Leakey points out in a moving last chapter that we need to do this to avoid the many great dangers that threaten. ‘The work ... described in this book surely demonstrates that Homo sapiens derives from a single stock ... With our global perspective comes a global responsibility ... both for other members of the human race and for the many forms of life with which we share our world.’ Such admonitions are not new but they are fundamentally important. It is good to find them so firmly stated as the conclusions to a study of prehistory.