It is obvious that humans are unlike all animals. It is also obvious that we are a species of big mammal, down to the minutest details of our anatomy and our molecules. That contradiction is the most fascinating feature of the human species. It is familiar, but we still have difficulty grasping how it came to be and what it means.
On the one hand, between ourselves and all other species lies a seemingly unbridgeable gulf that we acknowledge by defining a category called 'animals'. It implies that we consider centipedes, chimpanzees, and clams to share decisive features with each other but not with us, and to lack features restricted to us. Among these characteristics unique to us are the abilities to talk, write, and build complex machines. We depend completely on tools, not just on our bare hands, to make a living. Most of us wear clothes and enjoy art, and many of us believe in a religion. We are distributed over the whole Earth, command much of its energy and production, and are beginning to expand into the ocean depths and into space. We are also unique in darker attributes, including genocide, delight in torture, addictions to toxic drugs, and extermination of other species by the thousands. While a few animal species have one or two of these attributes in rudimentary form (like tool use), we still far eclipse animals even in those respects.
Thus, for practical and legal purposes, humans are not animals. When Darwin intimated in 1859 that we had evolved from apes, it is no wonder that most people initially regarded his theory as absurd and continued to insist that we had been separately created by God. Many people, including a quarter of all American college graduates, still hold to that belief today. On the other hand, we obviously are animals, with the usual animal body parts, molecules, and genes. It is even clear what particular type of animal we are. Externally, we are so similar to chimpanzees that eighteenth-century anatomists who believed in divine creation could already recognize our affinities. Just imagine taking some normal people, stripping off their clothes, taking away all their other possessions, depriving them of the power of speech, and reducing them to grunting, without changing their anatomy at all. Put them in a cage in the zoo next to the chimp cages, and let the rest of us clothed and talking people visit the zoo. Those speechless caged people would be seen for what we all really are: a chimp that has little hair and walks upright. A zoologist from outer space would immediately classify us as just a third species of chimpanzee, along with the pygmy chimp of Zaire and the common chimp of the rest of tropical Africa.
Molecular genetic studies over the last half-a-dozen years have shown that we continue to share over ninety-eight per cent of our genes with the other two chimps. The overall genetic distance between us and chimps is even smaller than the distance between such closely related bird species as red-eyed and white-eyed vireos, or willow warblers and chiffchaffs. So we still carry most of our old biological baggage with us. Since Darwin's time, fossilized bones of hundreds of creatures variously intermediate between apes and modern humans have been discovered, making it impossible for a reasonable person to deny the overwhelming evidence. What once seemed absurd—our evolution from apes—actually happened.
Yet the discoveries of many missing links have only made the problem more fascinating, without fully solving it. The few bits of new baggage we acquired—the two per cent of our genes that differ from those of chimps—must have been responsible for all of our seemingly unique properties. We underwent some small changes with big consequences rather quickly and recently in our evolutionary history. In fact, as recently as a hundred thousand years ago that zoologist from outer space would have viewed us as just one more species of big mammal. Granted, we had a couple of curious behavioural habits, notably our control of fire and our dependence on tools, but those habits would have seemed no more curious to the extraterrestrial visitor than would the habits of beavers and bowerbirds. Somehow, within a few tens of thousands of years—a time that is almost infinitely long when measured against one person's memory but is only a tiny fraction of our species' separate history—we had begun to demonstrate the qualities that make us unique and fragile.
What were those few key ingredients that made us human? Since our unique properties appeared so recently and involved so few changes, those properties or at least their precursors must already be present in animals. What are those animal precursors of art and language, of genocide and drug abuse?
Our unique qualities have been responsible for our present biological success as a species. No other large animal is native to all the continents, or breeds in all habitats from deserts and the Arctic to tropical rainforests. No large wild animal rivals us in numbers. But among our unique qualities are two that now jeopardize our existence: our propensities to kill each other and to destroy our environment. Of course, both propensities occur in other species: lions and many other animals kill their own kind, while elephants and others damage their environment. However, these propensities are much more threatening in us than in other animals because of our technological power and exploding numbers.
There is nothing new about prophecies to the effect that the end of the world is near if we do not repent. What is new is that such a prophecy is now true, for two obvious reasons. First, nuclear weapons give us the means to wipe ourselves out quickly: no humans possessed this means before.
Second, we already appropriate about forty per cent of the Earth's net productivity (that is, the net energy captured from sunlight). With the world's human population now doubling every forty-one years, we will soon have reached the biological limit to growth, at which point we will have to start fighting each other in deadly earnest for a slice of the world's fixed pie of resources. In addition, given the present rate at which we are exterminating species, most of the world's species will become extinct or endangered within the next century, but we depend on many species for our own life support.
Why rehearse these familiar depressing facts? Why try to trace the animal origins of our destructive qualities? If they really are part of our evolutionary heritage, that seems to imply that they are genetically fixed and hence unchangeable.
In fact, our situation is not hopeless. Perhaps the urge to murder strangers or sexual rivals is innate in us, but that still has not prevented human societies from attempting to thwart those instincts, and from succeeding in sparing most people the fate of being murdered. Even taking two world wars into account, proportionately far fewer people have suffered violent deaths in twentiethcentury industrialized states than in stone-age tribal societies. Many modern populations enjoy longer lifespans than did humans of the past. Environmentalists do not always lose in battles with developers and destroyers. Even some genetic infirmities, such as phenylketonuria andjuvenile-onset diabetes, can now be mitigated or cured. Therefore, my purpose in rehearsing our situation is to help us avoid repeating our mistakes—to use knowledge of our past and our propensities in order to change our behaviour. That is the hope behind the dedication of this book. My twin sons were born in 1987 and will reach my present age in the year 2040. What we are doing now is shaping their world.
It is not the goal of this book to propose specific solutions to our predicament, because the solutions we should adopt are already clear in broad outline. Some of those solutions include halting population growth, limiting or eliminating nuclear weapons, developing peaceful means for solving international disputes, reducing our impact on the environment, and preserving species and natural habitats. Many excellent books make detailed proposals on how to carry out these policies. Some of these policies are being implemented in some cases now; we 'just' need to implement them consistently. If we all became convinced today that they were essential, we would already know enough to start carrying them out tomorrow. What is lacking is the necessary political will. Hence I seek to foster that will, by tracing in this book our history as a species. Our problems have deep roots tracing back to our animal ancestry. They have been growing for a long time with our increasing power and numbers, and are now steeply accelerating. We can convince ourselves of the inevitable outcome of our current shortsighted practices just by examining the many past societies that destroyed themselves by destroying their own resources, despite having less potent means of self-destruction than ours. Political historians justify the study of individual states and rulers by the opportunity to learn from the past. That justification applies even more so to the study of our history as a species, because the lessons of that study are simpler and clearer.
The story of our rise and fall divides into five natural parts. In the first part (Chapters One and Two) we shall follow our history from several million years ago until just before the appearance of agriculture ten thousand years ago. These two chapters deal with the evidence of bones, tools, and genes—the evidence that is preserved in the archaeological and biochemical record, and that gives us our most direct information about how we have changed. Fossilized bones and tools can often be dated, permitting us to deduce just when we changed. We shall examine the basis of the conclusion that we are still ninety-eight per cent chimps in our genes, and try to figure out what in the remaining two per cent was responsible for our great leap forward. The second part (Chapters Three to Seven) deals with changes in the human life-cycle, which were as essential to the development of language and art as were the skeletal changes discussed in Part One. It is restating the obvious to mention that we feed our children after the age of weaning, instead of leaving them to find food on their own; that most adult men and women associate in couples; that most fathers as well as mothers care for their children; that many people live long enough to experience being grandparents; and that women undergo menopause. To us, these traits are the norm, but by the standards of our closest animal relatives they are bizarre. They constitute major changes from our ancestral condition, PROLOGUE though they do not fossilize and so we do not know when they arose. For that reason they receive much briefer treatment in human paleontology texts than do our changes in brain size and pelvis, but they were crucial to our uniquely human cultural development, and merit equal attention. With Parts One and Two having surveyed the biological underpinnings of our cultural flowering, Part Three (Chapters Eight to Twelve) considers the cultural traits that we believe distinguish us from animals. Those that come to mind first are the ones of which we are proudest: language, art, technology, and agriculture, the hallmarks of our rise. Yet our distinguishing cultural traits also include black marks on our record, such as abuse of toxic chemicals. While one can debate whether all these hallmarks rank as uniquely human, they at least constitute huge advances on animal precursors. But animal precursors there must have been, since these traits flowered only recently on an evolutionary time scale. What were those precursors? Was their flowering inevitable in the history of life on Earth, for example, so inevitable that we expect there to be many other planets out in space, inhabited by creatures as advanced as ourselves? Besides chemical abuse, our self-destructive traits include two serious enough that they may lead to our fall. Part Four (Chapters Thirteen to Sixteen) considers the first of these: our propensity for xenophobic killing of other human groups. This trait has direct animal precursors—namely, the contests between competing individuals and groups that, in many species besides our own, may be resolved by murder. We have merely used our technological prowess to improve our killing power. In Part Four we shall consider the xenophobia and extreme isolation that marked the human condition before the rise of political states began to make us more homogenous culturally. We shall see how technology, culture, and geography affected the outcome of two of the most familiar historical sets of contests between human groups. We shall then survey the worldwide recorded history of xenophobic mass murder. This is painful material, but here above all is an example of how our refusal to face up to our history condemns us to repeat past mistakes on a more dangerous scale. The other dark trait that now threatens our survival is our accelerating assault on our environment.
This too has its direct animal precursors. Animal populations that for one reason or another escaped control by predators and parasites have in some cases also escaped their own internal controls on their numbers, multiplied until they damaged their resource base, and occasionally have eaten their way into extinction. Such a risk applies with special force to humans, because predation on us is now negligible, no habitat is beyond our influence, and our power to kill individual animals and destroy habitats is unprecedented. Unfortunately, many people still cling to the Rousseau-esque fantasy that this tendency appeared in us only with the Industrial Revolution, before which we lived in harmony with Nature. If that were true, we would have nothing to learn from the past except how virtuous we once were, and how evil we have now become. Hence Part Five (Seventeen to Nineteen) seeks to dismantle this fantasy by facing up to our long history of environmental mismanagement. In Part Five as in Part Four, the emphasis is on recognizing that our present situation is not novel, except in degree. The experiment has already been run many times, and the outcome is there for us to learn from.
This book concludes with an epilogue that traces our rise from animal status. It also traces the acceleration in our means to bring about our fall. I would not have written this book if I thought that the risk was remote, but I also would not have written it if I considered our situation hopeless. Lest any readers get so discouraged by our track record and present predicament that they overlook this message, I point out the hopeful signs and the ways in which we can learn from the past. For those of you who would like suggestions for further reading, a section at the end will guide you to more books and articles on the material of each chapter. A volume that ranges over such a broad canvas as this one has to be selective. Every reader is bound to find some absolutely crucial favourite subjects omitted and some other subjects pursued in inordinate detail. So that you will not feel you were misled, I shall lay out at the start my own particular interests, and where they come from.
My father is a physician, my mother a musician with a gift for languages. Whenever I was asked as a child about my career plans, my response was that I wanted to be a doctor like my father. By my last year in college, that goal had become gently transformed into the related goal of medical research, and so I trained in physiology, the area in which I now teach and do research at the University of California Medical School in Los Angeles.
However, I had also become interested at the age of seven in bird-watching, and I had been fortunate to go to a school that let me delve into languages and history. After I got my PhD., the prospect of devoting the rest of my life to the single professional interest of physiology began to look increasingly oppressive. At that point a happy constellation of events and people gave me the chance to spend a summer in the highlands of New Guinea. Ostensibly, the purpose of my trip—was to measure nesting success of New Guinea birds, a project that collapsed dismally within a few weeks when I found myself unable to locate even a single bird's nest in the jungle. Yet the real purpose of the trip succeeded completely: to indulge my thirst for adventure and bird-watching in one of the wildest remaining parts of the world. What I saw then of New Guinea's fabulous birds, including its bowerbirds and birds of paradise, led me to develop a parallel second career in bird ecology, evolution, and biogeography. Since then, I have returned to New Guinea and the neighbouring Pacific islands a dozen times to pursue my bird research.
I found it hard to work in New Guinea amid the accelerating destruction of the birds and forests that I loved, without getting involved in conservation biology. So I began to combine my academic research with practical work as a consultant for governments, by applying what I knew about animal distributions to designing national park systems and surveying their proposed national parks. It was also hard to work in New Guinea, where languages replace each other every twenty miles, and where learning bird names in each local language proved to be the key to tapping New Guineans' encyclopedic knowledge of their birds, without returning to my earlier interest in languages. Most of all, it was hard to study the evolution and extinction of bird species without wanting to understand the evolution and possible extinction of Homo sapiens, by far the most interesting species of all. That interest, too, was especially difficult to ignore in New Guinea, with its enormous human diversity.
Those are the paths by which I came to be interested in the particular aspects of humans that are emphasized in this book. I do not feel as if I am thereby making excuses for inappropriately slanted coverage. Numerous excellent books by anthropologists and archaeologists already discuss human evolution in terms of tools and bones, which this book can therefore summarize more briefly. However, those other volumes devote much less space to my particular interests of the human life-cycle, human geography, human impact on the environment, and humans as animals. Those subjects are as central to human evolution as are the more traditional subjects involving tools and bones.
What may at first seem here to be a plethora of examples drawn from New Guinea is also, I believe, appropriate. Granted, New Guinea is just one island, located in a particular part of the world (the tropical Pacific), and hardly providing a random cross-section of modern humanity. But New Guinea harbours a much bigger slice of humanity than you would at first guess from its area. About a thousand of the world's approximately 5,000 languages are spoken only in New Guinea. Much of the cultural diversity that survives in the modern world is contained within New Guinea. All highland peoples in New Guinea's mountainous interior were stone-age farmers until very recently, while many lowland groups were nomadic hunter-gatherers and fishermen practising somewhat casual agriculture. Local xenophobia was extreme, cultural diversity correspondingly so, and travel outside one's tribal territory would have been suicidal. Many of the New Guineans who have worked with me are deadly and expert hunters who lived out their childhood in the days of stone tools and xenophobia. Thus, New Guinea is as good a model as we have left today of what much of the rest of the human world was like until recently.