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  Eventually, it was the barbarians rather than Romans who won the battles: what was the fundamental reason for that shift in fortune? Was it because of changes in the barbarians themselves, such that they became more numerous or better organized, acquired better weapons or more horses, or profited from climate change in the Central Asian steppes? In that case, we would say that barbarians really could be identified as the fundamental cause of Rome’s fall. Or was it instead that the same old unchanged barbarians were always waiting on the Roman Empire’s frontiers, and that they couldn’t prevail until Rome became weakened by some combination of economic, political, environmental, and other problems? In that case we would blame Rome’s fall on its own problems, with the barbarians just providing the coup de grâce. This question continues to be debated. Essentially the same question has been debated for the fall of the Khmer Empire centered on Angkor Wat in relation to invasions by Thai neighbors, for the decline in Harappan Indus Valley civilization in relation to Aryan invasions, and for the fall of Mycenean Greece and other Bronze Age Mediterranean societies in relation to invasions by Sea Peoples.

  The fourth set of factors is the converse of the third set: decreased support by friendly neighbors, as opposed to increased attacks by hostile neighbors. All but a few historical societies have had friendly trade partners as well as neighboring enemies. Often, the partner and the enemy are one and the same neighbor, whose behavior shifts back and forth between friendly and hostile. Most societies depend to some extent on friendly neighbors, either for imports of essential trade goods (like U.S. imports of oil, and Japanese imports of oil, wood, and seafood, today), or else for cultural ties that lend cohesion to the society (such as Australia’s cultural identity imported from Britain until recently). Hence the risk arises that, if your trade partner becomes weakened for any reason (including environmental damage) and can no longer supply the essential import or the cultural tie, your own society may become weakened as a result. This is a familiar problem today because of the First World’s dependence on oil from ecologically fragile and politically troubled Third World countries that imposed an oil embargo in 1973. Similar problems arose in the past for the Greenland Norse, Pitcairn Islanders, and other societies.

  The last set of factors in my five-point framework involves the ubiquitous question of the society’s responses to its problems, whether those problems are environmental or not. Different societies respond differently to similar problems. For instance, problems of deforestation arose for many past societies, among which Highland New Guinea, Japan, Tikopia, and Tonga developed successful forest management and continued to prosper, while Easter Island, Mangareva, and Norse Greenland failed to develop successful forest management and collapsed as a result. How can we understand such differing outcomes? A society’s responses depend on its political, economic, and social institutions and on its cultural values. Those institutions and values affect whether the society solves (or even tries to solve) its problems. In this book we shall consider this five-point framework for each past society whose collapse or persistence is discussed.

  I should add, of course, that just as climate change, hostile neighbors, and trade partners may or may not contribute to a particular society’s collapse, environmental damage as well may or may not contribute. It would be absurd to claim that environmental damage must be a major factor in all collapses: the collapse of the Soviet Union is a modern counter-example, and the destruction of Carthage by Rome in 146 B.C. is an ancient one. It’s obviously true that military or economic factors alone may suffice. Hence a full title for this book would be “Societal collapses involving an environmental component, and in some cases also contributions of climate change, hostile neighbors, and trade partners, plus questions of societal responses.” That restriction still leaves us ample modern and ancient material to consider.

  Issues of human environmental impacts today tend to be controversial, and opinions about them tend to fall on a spectrum between two opposite camps. One camp, usually referred to as “environmentalist” or “pro-environment,” holds that our current environmental problems are serious and in urgent need of addressing, and that current rates of economic and population growth cannot be sustained. The other camp holds that environmentalists’ concerns are exaggerated and unwarranted, and that continued economic and population growth is both possible and desirable. The latter camp isn’t associated with an accepted short label, and so I shall refer to it simply as “non-environmentalist.” Its adherents come especially from the world of big business and economics, but the equation “non-environmentalist” = “pro-business” is imperfect; many businesspeople consider themselves environmentalists, and many people skeptical of environmentalists’ claims are not in the world of big business. In writing this book, where do I stand myself with the respect to these two camps?

  On the one hand, I have been a bird-watcher since I was seven years old. I trained professionally as a biologist, and I have been doing research on New Guinea rainforest birds for the past 40 years. I love birds, enjoy watching them, and enjoy being in rainforest. I also like other plants, animals, and habitats and value them for their own sakes. I’ve been active in many efforts to preserve species and natural environments in New Guinea and elsewhere.

  For the past dozen years I’ve been a director of the U.S. affiliate of World Wildlife Fund, one of the largest international environmentalist organizations and the one with the most cosmopolitan interests. All of those things have earned me criticism from non-environmentalists, who use phrases such as “fearmonger,” “Diamond preaches gloom and doom,” “exaggerates risks,” and “favors endangered purple louseworts over the needs of people.” But while I do love New Guinea birds, I love much more my sons, my wife, my friends, New Guineans, and other people. I’m more interested in environmental issues because of what I see as their consequences for people than because of their consequences for birds.

  On the other hand, I have much experience, interest, and ongoing involvement with big businesses and other forces in our society that exploit environmental resources and are often viewed as anti-environmentalist. As a teenager, I worked on large cattle ranches in Montana, to which, as an adult and father, I now regularly take my wife and my sons for summer vacations. I had a job on a crew of Montana copper miners for one summer. I love Montana and my rancher friends, I understand and admire and sympathize with their agribusinesses and their lifestyles, and I’ve dedicated this book to them. In recent years I’ve also had much opportunity to observe and become familiar with other large extractive companies in the mining, logging, fishing, oil, and natural gas industries. For the last seven years I’ve been monitoring environmental impacts in Papua New Guinea’s largest producing oil and natural gas field, where oil companies have engaged World Wildlife Fund to provide independent assessments of the environment. I have often been a guest of extractive businesses on their properties, I’ve talked a lot with their directors and employees, and I’ve come to understand their own perspectives and problems.

  While these relationships with big businesses have given me close-up views of the devastating environmental damage that they often cause, I’ve also had close-up views of situations where big businesses found it in their interests to adopt environmental safeguards more draconian and effective than I’ve encountered even in national parks. I’m interested in what motivates these differing environmental policies of different businesses. My involvement with large oil companies in particular has brought me condemnation from some environmentalists, who use phrases such as “Diamond has sold out to big business,” “He’s in bed with big businesses,” or “He prostitutes himself to the oil companies.”

  In fact, I am not hired by big businesses, and I describe frankly what I see happening on their properties even though I am visiting as their guest.

  On some properties I have seen oil companies and logging companies being destructive, and I have said so; on other properties I have seen them being careful, and that was what I said. M
y view is that, if environmentalists aren’t willing to engage with big businesses, which are among the most powerful forces in the modern world, it won’t be possible to solve the world’s environmental problems. Thus, I am writing this book from a middle-of-the-road perspective, with experience of both environmental problems and of business realities.

  How can one study the collapses of societies “scientifically”? Science is often misrepresented as “the body of knowledge acquired by performing replicated controlled experiments in the laboratory.” Actually, science is something much broader: the acquisition of reliable knowledge about the world. In some fields, such as chemistry and molecular biology, replicated controlled experiments in the laboratory are feasible and provide by far the most reliable means to acquire knowledge. My formal training was in two such fields of laboratory biology, biochemistry for my undergraduate degree and physiology for my Ph.D. From 1955 to 2002 I conducted experimental laboratory research in physiology, at Harvard University and then at the University of California in Los Angeles.

  When I began studying birds in New Guinea rainforest in 1964, I was immediately confronted with the problem of acquiring reliable knowledge without being able to resort to replicated controlled experiments, whether in the laboratory or outdoors. It’s usually neither feasible, legal, nor ethical to gain knowledge about birds by experimentally exterminating or manipulating their populations at one site while maintaining their populations at another site as unmanipulated controls. I had to use different methods. Similar methodological problems arise in many other areas of population biology, as well as in astronomy, epidemiology, geology, and paleontology.

  A frequent solution is to apply what is termed the “comparative method” or the “natural experiment”—i.e., to compare natural situations differing with respect to the variable of interest. For instance, when I as an ornithologist am interested in effects of New Guinea’s Cinnamon-browed Melidectes Honeyeater on populations of other honeyeater species, I compare bird communities on mountains that are fairly similar except that some do and others don’t happen to support populations of Cinnamon-browed Melidectes Honeyeaters. Similarly, my books The Third Chimpanzee: The Evolution and Future of the Human Animal and Why Is Sex Fun? The Evolution of Human Sexuality compared different animal species, especially different species of primates, in an effort to figure out why women (unlike females of most other animal species) undergo menopause and lack obvious signs of ovulation, why men have a relatively large penis (by animal standards), and why humans usually have sex in private (rather than in the open, as almost all other animal species do). There is a large scientific literature on the obvious pitfalls of that comparative method, and on how best to overcome those pitfalls. Especially in historical sciences (like evolutionary biology and historical geology), where it’s impossible to manipulate the past experimentally, one has no choice except to renounce laboratory experiments in favor of natural ones.

  This book employs the comparative method to understand societal collapses to which environmental problems contribute. My previous book (Guns, Germs, and Steel: The Fates of Human Societies) had applied the comparative method to the opposite problem: the differing rates of buildup of human societies on different continents over the last 13,000 years. In the present book focusing instead on collapses rather than on buildups, I compare many past and present societies that differed with respect to environmental fragility, relations with neighbors, political institutions, and other “input” variables postulated to influence a society’s stability. The “output” variables that I examine are collapse or survival, and form of the collapse if a collapse does occur. By relating output variables to input variables, I aim to tease out the influence of possible input variables on collapses.

  A rigorous, comprehensive, and quantitative application of this method was possible for the problem of deforestation-induced collapses on Pacific islands. Prehistoric Pacific peoples deforested their islands to varying degrees, ranging from only slight to complete deforestation, and with societal outcomes ranging from long-term persistence to complete collapses that left everybody dead. For 81 Pacific islands my colleague Barry Rolett and I graded the extent of deforestation on a numerical scale, and we also graded values of nine input variables (such as rainfall, isolation, and restoration of soil fertility) postulated to influence deforestation. By a statistical analysis we were able to calculate the relative strengths with which each input variable predisposed the outcome to deforestation. Another comparative experiment was possible in the North Atlantic, where medieval Vikings from Norway colonized six islands or land masses differing in suitability for agriculture, ease of trade contact with Norway, and other input variables, and also differing in outcome (from quick abandonment, to everybody dead after 500 years, to still thriving after 1,200 years). Still other comparisons are possible between societies from different parts of the world.

  All of these comparisons rest on detailed information about individual societies, patiently accumulated by archaeologists, historians, and other scholars. At the end of this book I provide references to the many excellent books and papers on the ancient Maya and Anasazi, the modern Rwandans and Chinese, and the other past and present societies that I compare. Those individual studies constitute the indispensable database for my book. But there are additional conclusions that can be drawn from comparisons among those many societies, and that could not have been drawn from detailed study of just a single society. For example, to understand the famous Maya collapse requires not only accurate knowledge of Maya history and the Maya environment; we can place the Maya in a broader context and gain further insights by comparing them with other societies that did or didn’t collapse, and that resembled the Maya in some respects and differed from them in other respects. Those further insights require the comparative method.

  I have belabored this necessity for both good individual studies and good comparisons, because scholars practicing one approach too often belittle the contributions of the other approach. Specialists in the history of one society tend to dismiss comparisons as superficial, while those who compare tend to dismiss studies of single societies as hopelessly myopic and of limited value for understanding other societies. But we need both types of studies if we are to acquire reliable knowledge. In particular, it would be dangerous to generalize from one society, or even just to be confident about interpreting a single collapse. Only from the weight of evidence provided by a comparative study of many societies with different outcomes can one hope to reach convincing conclusions.

  So that readers will have some advance idea where they are heading, here is how this book is organized. Its plan resembles a boa constrictor that has swallowed two very large sheep. That is, my discussions of the modern world and also of the past both consist of a disproportionately long account of one society, plus briefer accounts of four other societies.

  We shall begin with the first large sheep. Part One comprises a single lengthy chapter (Chapter 1), on the environmental problems of southwestern Montana, where Huls Farm and the ranches of my friends the Hirschys (to whom this book is dedicated) are located. Montana has the advantage of being a modern First World society whose environmental and population problems are real but still relatively mild compared to those of most of the rest of the First World. Above all, I know many Montanans well, so that I can connect the policies of Montana society to the often-conflicting motivations of individual people. From that familiar perspective of Montana, we can more easily imagine what was happening in the remote past societies that initially strike us as exotic, and where we can only guess what motivated individual people.

  Part Two begins with four briefer chapters on past societies that did collapse, arranged in a sequence of increasing complexity according to my five-point framework. Most of the past societies that I shall discuss in detail were small and peripherally located, and some were geographically bounded, or socially isolated, or in fragile environments. Lest the reader thereby be misled into concluding tha
t they are poor models for familiar big modern societies, I should explain that I selected them for close consideration precisely because processes unfolded faster and reached more extreme outcomes in such small societies, making them especially clear illustrations. It is not the case that large central societies trading with neighbors and located in robust environments didn’t collapse in the past and can’t collapse today. One of the past societies that I do discuss in detail, the Maya, had a population of many millions or tens of millions, was located within one of the two most advanced cultural areas of the New World before European arrival (Mesoamerica), and traded with and was decisively influenced by other advanced societies in that area. I briefly summarize in the Further Readings section for Chapter 9 some of the many other famous past societies—Fertile Crescent societies, Angkor Wat, Harappan Indus Valley society, and others—that resembled the Maya in those respects, and to whose declines environmental factors contributed heavily.

  Our first case study from the past, the history of Easter Island (Chapter 2), is as close as we can get to a “pure” ecological collapse, in this case due to total deforestation that led to war, overthrow of the elite and of the famous stone statues, and a massive population die-off. As far as we know, Easter’s Polynesian society remained isolated after its initial founding, so that Easter’s trajectory was uninfluenced by either enemies or friends. Nor do we have evidence of a role of climate change on Easter, though that could still emerge from future studies. Barry Rolett’s and my comparative analysis helps us understand why Easter, of all Pacific islands, suffered such a severe collapse.