It has long been suspected that many of those mysterious abandonments were at least partly triggered by ecological problems: people inadvertently destroying the environmental resources on which their societies depended. This suspicion of unintended ecological suicide —ecocide— has been confirmed by discoveries made in recent decades by archaeologists, climatologists, historians, paleontologists, and palynologists (pollen scientists). The processes through which past societies have undermined themselves by damaging their environments fall into eight categories, whose relative importance differs from case to case: deforestation and habitat destruction, soil problems (erosion, salinization, and soil fertility losses), water management problems, overhunting, overfishing, effects of introduced species on native species, human population growth, and increased per-capita impact of people.

(Jared Diamond: Collapse, p. 6)

The risk of such collapses today is now a matter of increasing concern; indeed, collapses have already materialized for Somalia, Rwanda, and some other Third World countries. Many people fear that ecocide has now come to overshadow nuclear war and emerging diseases as a threat to global civilization. The environmental problems facing us today include the same eight that undermined past societies, plus four new ones: human-caused climate change, buildup of toxic chemicals in the environment, energy shortages, and full human utilization of the Earth's photynthetic capacity. Most of these 12 threats, it is claimed, will become globally critical within the next few decades: either we solve the problems by then, or the problems will undermine not just Somalia but also First World societies. Much more likely than a doomsday scenario involving human extinction or an apocalyptic collapse of industrial civilization would be "just" a future of significantly lower living standards, chronically higher risks, and the undermining of what we now consider some of our key values. Such a collapse could assume various forms, such as the worlwide spread of diseases or else of wars, triggered ultimately by scarcity of environmental resources. If this reasoning is correct, then our efforts today will determine the state of the world in which the current generation of children and young adults lives out their middle and late years.

(Jared Diamond: Collapse, p. 7)

In fact, both extreme sides in this controversy —the racists and the believers in a past Eden— are committing the error of viewing past indingenous peoples as fundamentally different from (whether inferior to or superior to) modern First World peoples. Managing environmental resources sustainably has always been difficult, ever since Homo sapiens developed modern inventiveness, efficiency, and hunting skills by around 50,000 years ago. Beginning with the first human colonization of the Australian continent around 46,000 years ago, and the subsequent prompt extinction of most of Australia's former giant marsupials and other large animals, every human colonization of a land mass formerly lacking humans —whether of Australia, North America, South America, Madagascar, the Mediterranean islands, or Hawaii and New Zealand and dozens of other Pacific islands— has been followed by a wave of extinction of large animals that had evolved without fear of humans and were easy to kill, or else succumbed to human-associated habitat changes, introduced pest species, and diseases. Any people can fall into the trap of overexploiting environmental resources, because of ubiqutous problems that we shall consider later in this book: that the resources initially seem inexhaustibly abundant; that signs of their incipient depletion become masked by normal fluctuations in resource levels between years or decades; that it's difficult to get people to agree on exercising restraint in harvesting a shared resource (the so-called tragedy of the commons, to be discussed in later chapters); and that the complexity of ecosystems often makes the consequences of some human-caused perturbation virtually impossible to predict even for a professional ecologist. Environmental problems that are hard to manage today were surely even harder to manage in the past. Especially for past non-literate peoples who couldn't read case studies of societal collapses, ecological damage constituted a tragic, unforeseen, unintended consequence of their best efforts, rather than morally culpable blind or conscious selfishness. The societies that ended up collapsing were (like the Maya) among the most creative and (for a time) advanced and successful of their times, rather than stupid and primitive.

(Jared Diamond: Collapse, pp. 9-10)

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 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 Melidected 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 enviromental 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.

(Jared Diamond: Collapse, pp. 17-18)

Part one: modern Montana.

I initially wondered whether Montana's environmental problems and polarizing disputes might involve selfish behavior on the part of individuals who advanced their own interests in full knowledge that they were simultaneously damaging the rest of Montana society. This may be true in some cases, such as the proposals of some mining executives to carry out cyanide heap-leach gold extraction despite the abundant evidence of resulting toxicity problems; the transfers of deer and elk between game farms by some farm owner despite the known resulting risk of spreading chronic wasting disease; and the illegal introductions of pike into lakers and rivers by some fishermen for their own fishing pleasure, despite the history of such transfers having destroyed many other fisheries. Even in the cases, though, I haven't interviewed individuals involved and don't know whether they could honestly claim that they thought they had been acting safely. Whenever I have actually been able to talk with Montanans, I have found their actions to be consistent with their values, even if those values clash with my own or those of other Montanans. That is, for the most part Montana's difficulties cannot be simplistically attributed to selfish evil people knowingly and reprehensibily profiting at the expense of neighbors. Instead, they involve clashes between people whose own particular backgrounds and values cause them to favor policies differing from those favored by people with different backgrounds and values. (...)

(Jared Diamond: Collapse, p. 57)

Steve Powell explained to me, "People used to expect no more of a farm than to produce enough to feed themselves; today, they want more out of life than just getting fed; they want to earn enough to send their kids to college." When John Cook was growing up on a farm with his parents, "At dinnertime, my mother was satisfied to go to the orchard and gather asparagus, and as a boy I was satisfied for fun to go hunting and fishing. Now, kids expect fast food and HBO; if their parents don't provide that, they feel deprived compared to their peers. In my days a young adult expected to be poor for the next 20 year, and only thereafter, if you were lucky, might you hope to end up more comfortably. Now, young adults expect to be comfortable early; a kid's first questions about a job are 'What are they pay, the hours, and the vacations?'" Every Montana farmer whom I know, and who loves being a farmer, is either very concerned whether any of his/her children will want to carry on the family farm, or already knows that none of them will.

(Jared Diamond: Collapse, p. 58)

It may initially have seemed absurd to select Montana as the subject of this first chapter of a book on societal collapses. Neither Montana in particular, nor the US in general, is in imminent danger of collapse. But: please reflect that half of the income of Montana residents doesn't come from their work within Montana, but instead consists of money flowing into Montana from other US states: federal government transfer payments (such as Social Security, Medicare, Medicare, Medicaid, and poverty programs) and private out-of-state funds (out-of-state pensions, earnings on real estate equity, and business income). That is, Montana's own economy already falls far short of supporting the Montana lifestyle, which is instead supported by and dependent on the rest of the US. If Montana were an isolated island, as Easter Island in the Pacific Ocean was in Polynesian times before European arrival, its present First World economy would already have collapsed, nor could it have developed that economy in the first place.

(Jared Diamond: Collapse, p. 74)

Second part: past societies. Easter Island.

The overall picture for Easter is the most extreme example of forest destruction in the Pacific, and among the most extreme in the world: the whole forest gone, and all of its tree species extinct. Immediate consequences for the islanders were losses of raw materials, losses of wild-caught foods, and decreased crop yields.

(Jared Diamond: Collapse, p. 107)

Objections to the idea that Easter Islanders may have inflicted the problems on themselves due to bad management of their natural resources:

A third objection is that Easter Islanders surely wouldn't have been so foolish as to cut down all their trees, when the consequences would have been so obvious to them. As Catherine Orliac expressed it, "Why destroy a forest that one needs for his [i.e., the Easter Islanders'] material and spiritual survival?" This is indeed a key question, one that has nagged not only Catherine Orliac but also my University of California students, me, and everyone else who has wondered about self-inflicted environmental damage. I have often asked myself, "What did the Easter Islander who cut down the last palm tree say while he was doing it?" Like modern loggers, did he shout "Jobs, not trees!"? Or: "Technology will solve our problems, never fear, we'll find a substitute for wood"? Or: "We don't have proof that there aren't palms somewhere else on Easter, we need more research, your proposed ban on logging is premature and driven by fear-mongering"? Similar questions arise for every society that has inadvertently damaged its environment. When we return to this question in Chapter 14, we shall see that there is a whole series of reasons why societies nevertheless do make such mistakes.

(Jared Diamond: Collapse, p. 114)

The Easter Islanders' isolation probably also explains why I have found that their collapse, more than the collapse of any other pre-industrial society, haunts my readers and students. The parallels between Easter Island and the whole modern world are chillingly obvious. Thanks to globalization, international trade, jet planes, and the Internet, all countries on Earth today share resources and affect each other, just as did Easter's dozen clans. Polynesian Easter Island was as isolated in the Pacific Ocean as the Earth is today in space. When the Easter Islanders got into difficulties, there was nowhere to which they could flee, nor to which they could turn for help; nor shall we modern Earthlings have recourse elsewhere if our troubles increase. Those are the reasons why people see the collapse of Easter Island society as a metaphor, a worst-case scenario, for what may lie ahead of us in our own future.

(Jared Diamond: Collapse, p. 119)

Pitcairn and Henderson islands:

Many centuries ago, immigrants came to a fertile land blessed with apparently inexhaustible natural resources. While the land lacked a few raw materials useful for industry, those materials were readily obtained by overseas trade with poorer lands that happened to have deposits of them. For a time, all the lands prospered, and their populations multiplied.

But the population of the rich land eventually multiplied beyond the numbers that even its abundant resources could support. As its forests were felled and its soils eroded, its agricultural productivity was no longer sufficient to generate export surpluses, build ships, or even to nourish its own population. With that decline of trade, shortages of the imported raw materials developed. Civil war spread, as established political institutions were overthrown by a kaleidoscopically changing succession of local military leaders. The starving populace of the rich land survived by turning to cannibalism. Their former overseas trade partners met an even worse fate: deprived of the imports on which they had depended, they in turn ravaged their own environments until no one was left alive.

Does this grim scenario represent the future of the United States and our trade partners? We don't know yet, but the scenario has already played itself out on three tropical Pacific islands. One of them, Pitcairn Island, is famous as the "uninhabited" island to which the mutineers from the HMS Bounty fled in 1790. They chose Pitcairn because it was indeed uninhabited at that time, remote, and hence offered a hiding place from the vengeful British navy searching for them. But the mutineers did find temple platforms, petroglyphs, and stone tools giving mute evidence that Pitcairn had formerly supported an ancient Polynesian population. East of Pitcairn, an even more remote island named Henderson remains uninhabited to this day. Even now, Pitcairn and Henderson are among the most inaccessible islands in the world, without any air or scheduled sea traffic, and visited only by the occasional yacht or cruise ship. Yet Henderson, too, bears abundant marks of a former Polynesian population. What happened to those original Pitcairn Islanders, and to their vanished cousins on Henderson?

(Jared Diamond: Collapse, pp. 120-121)

With too many people and too little food, Mangareva society slid into a nightmare of civil war and chronic hunger, whose consequences are recalled in detail by modern islanders. For protein, people turned to cannibalism, in the form not only of eating freshly dead people but also of digging up and eating buried corpses. Chronic fighting broke out over the precious remaining cultivable land; the winning side redistributed the land of the losers. Instead of an orderly political system based on hereditary chiefs, non-hereditary warriors took over. The thought of Lilliputian military dictatorships on eastern and western Mangareva, battling for control of an island only five miles long, could seem funny if it were not so tragic. All that political chaos alone would have made it difficult to muster the manpower and supplies necessary for oceangoing canoe travel, and to go off for a month and leave one's garden undefended, even if trees for canoes themselves had not become unavailable. With the collapse of Mangareva at its hub, the whole East Polynesia trade network that had joined Mangareva to the Marquesas, Societies, Tuamotus, Pitcairn, and Henderson disintegrated, as documented by Weisler's sourcing studies of basalt adzes.

(Jared Diamond: Collapse, pp. 120-121)

The Anasazi and their neighbors:

Why would outlying settlements have supported the Chaco center, dutifully delivering timber, pottery, stone, turquoise, and food without receiving anything material in return? The answer is probably the same as the reason why outlying areas of Italy and Britain today support our cities such as Rome and London, which also produce no timber or food but serve as political and religious centers. Like the modern Italians and British, Chacoans were now irreversibly committed to living in a complex, interdependent society. They could no longer revert to their original condition of self-supporting mobile little groups, because the trees in the canyon were gone, the arroyos were cut below field levels, and the growing population had filled up the region and left no unoccupied suitable areas to which to move. When the pinyon and juniper trees were cut down, the nutrients in the litter underneath the trees were flushed out. Today, more than 800 years later, there is still no pinyon/juniper woodland growing anywhere near the packrat middens containing twigs of the woodland that had grown there before AD 1000. Food remains in rubbish at archaeological sites attest to the growing problems of the canyon's inhabitants in nourishing themselves: bits and mice. Remains of complete headless mice in human coprolites (preserved dry feces) suggest that people were catching mice in the fields, beheading them, and popping them in whole.

(Jared Diamond: Collapse, p. 150)

The final blow for Chacoans was a drought that tree rings show to have begun around AD 1130. There had been similar droughts previously, around AD 1090 and 1040, but the difference this time was that Chaco Canyon now held more people, more dependent on outlying settlements, and with no land left unoccupied. A drought would have caused the groundwater table to drop below the level where it could be tapped by plant roots and could support agriculture; a drought would also make rainfall-supported dryland agriculture and irrigation agriculture impossible. A drought that laste more than three years would have been fatal, because modern Puebloans can store corn for only two or three years, after which it is too rotten or infested to eat. Probably the outlying settlements that had formerly supplied the Chaco political and religious centers with food lost faith in the Chacoan priests whose prayers for rain remained unanswered, and they refused to make more food deliveries. A model for the end of Anasazi settlement at Chaco Canyon, which Europeans did not observe, is what happened in the Pueblo Indian revolt of 1860 against the Spaniards, a revolt that Europeans did observe. As in Chaco Anasazi centers, the Spaniards had extracted food from local farmers by taxing them, and those food taxes were tolerated until a drought left the farmers themselves short of food, provoking them to revolt.

(Jared Diamond: Collapse, pp. 152-153)

Despite these varying proximate causes of abandonments, all were ultimately due to the same fundamental challenge: people living in fragile and difficult environment, adopting solutions that were brilliantly successful and understandable "in the short run," but that failed or else created fatal problems in the long run, when people became confronted with external environmental challenges or human-caused environmental changes that societies without written histories and without archaeologists could not have anticipated. I put "in the short run" in quotation marks, because the Anasazi did survive in Chaco Canyon for about 600 years, considerably longer than the duration of European occupation anywhere in the New World since Columbus's arrival in AD 1492. During their existence, those various southwestern Native Americans experimented with half-a-dozen alternative types of economies (pp. 140-143). It took many centuries to discover that, among those economies, only the Pueblo economy was sustainable "in the long run," i.e., for at least a thousand years. That should make us modern Americans hesitate to be too confident yet about the sustainability of our First World economy, especially when we reflect how quickly Chaco society collapsed after its peak in the decade AD 1110-1120, and how implausible the risk of collapse would have seemed to Chacoans of that decade.

(Jared Diamond: Collapse, pp. 154-155)

From that perspective, we can propose a simple answer to the long-standing either/or debate: was Chaco Canyon abandoned because of human impact on the environment, or because of drought? The answer is: it was abandoned for both reasons. Over the course of six centuries the human population of Chaco Canyon grew, its demands on the environment grew, its environmental resources declined, and people came to be living increasingly close to the margin of what the environment could support. That was the ultimate cause of abandonment. The proximate cause, the proverbial last straw that broke the camel's back, was the drought that finally pushed Chacoans over the edge, a drought that a society living at a lower population density could have survived. When Chaco society did collapse, its inhabitants could no longer reconstruct their society in the way that the first farmers of the Chaco area had built up their society. The reason is that the initial conditions of abundant nearby trees, high groundwater levels, and a smooth floodplain without arroyos had disappeared.

(Jared Diamond: Collapse, p. 156)

The Maya collapses:

A further reason for our devoting a chapter to the Maya is to provide an antidote to our other chapters on past societies, which consist disproportionately of small societies in somewhat fragile and geographically isolated environments, and behind the cutting edge of contemporary technology and culture. The Maya were none of those things. Instead, they were culturally the most advanced society (or among the most advanced ones) in the pre-Columbian New World, the only one with extensive preserved writing, and located within one of the two heartland of New World citilization (Mesoamerica). While their environment did present some problems associated with its karst terrain and unpredictably fluctuating rainfall, it does not rank as notably fragile by world standards, and it was certainly less fragile than the environments of ancient Easter Island, the Anasazi area, Greenland, or modern Australia. Lest one be misled into thinking that crashes are a risk only for small peripheral societies in fragile areas, the Maya warn us that crashes can also befall the most advanced and creative societies.

(Jared Diamond: Collapse, p. 159)

Socially stratified societies, including modern American and European society, consist of farmers who produce food, plus non-farmers such as bureaucrats and soldiers who do not produce food but merely consume the food grown by the farmers and are in effect parasites on farmers. Hence in any stratified society the farmers must grow enough surplus food to meet not only their own needs but also those of the other consumers. The number of non-producing consumers that can be supported depends on the society's agricultural productivity. In the United States today, with its highly efficient agriculture, farmers make up only 2% of our population, and each farmer can feed on the average 125 other people (American non-farmers plus people in export martkets overseas). Ancient Egyptian agriculture, although much less efficient than modern mechanized agriculture, was still efficient enough for an Egyptian peasant to produce five times the food required for himself and his family. But a Maya peasant could produce only twice the needs of himself and his family. At least 70% of Maya society consisted of peasants. That's because Maya agriculture suffered from several limitations.

First, it yielded little protein. Corn, by far the dominant crop, has a lower protein content than the Old World staples of wheat and barley. The few edible domestic animals already mentioned included no large ones and yielded much less meat than did Old World cows, sheep, pigs, and goats. The Maya depended on a narrower range of crops than did Andean farmers (who in addition to corn also had potatoes, high-protein quinoa, and many other plants, plus llamas for meat), and much narrower again than the variety of crops in China and in western Eurasia.

Another limitation was that Maya corn agriculture was less intensive and productive than the Aztecs' chinampas (a very productive type of raised-field agriculture), the raised fields of the Tiwanaku civilization of the Andes, Moche irrigation on the coast of Peru, or fields tilled by animal-drawn plows over much of Eurasia.

Still a further limitation arose from the humid climate of the Maya area, which made it difficult to store corn beyond a year, whereas the Anasazi living in the dry climate of the US Southwest could store it for three years.

Finally, unlike Andean Indias with their llamas, and unlike Old World peoples with their horses, oxen, donkeys, and camels, the Maya had no animal-powered transport or plows. All overland transport for the Maya went on the backs of human porters. But if you send out a porter carrying a load of corn to accompany an army into the field, some of that load of corn is required to feed the porter himself on the trip out, and some more to feed him on the trip back, leaving only a fraction of the load available to feed the army. The longer the trip, the less of the load is left over from the porter's own requirements. Beyond a march of a few days to a week, it becomes un-economical to send porters carrying corn to provision armies or markets. Thus, the modest productivity of Maya agriculture, and their lack of draft animals, severely limited the duration and distance possible for their military campaigns.

(Jared Diamond: Collapse, pp. 164-165)

In the Maya area as elsewhere, the past is a lesson for the present. From the time of Spanish arrival, the Central Petén's population declined further to about 3,000 in AD 1714, as a result of deaths from diseases and other causes associated with Spanish occupation. By the 1960s, the Central Petén's population had risen back only to 25,000, still less than 1% of what it had been at the Classic Maya peak. Thereafter, however, immigrants flooded into the Central Petén, building up its population to abot 300,000 in the 1980s, and ushering in a new era of deforestation and erosion. Today, half of the Petén is once again deforested and ecologically degraded. One-quarter of all the forests of Honduras were destroyed between 1964 and 1989.

(Jared Diamond: Collapse, pp. 175-176)

To summarize the Classic Maya collapese, we can tentatively identify five strands. I acknowledge, however, that Maya archaeologists still disagree vigorously among themselves —in part, because the different strands evidently varied in importance among different parts of the Maya realm; because detailed archaeological studies are available only for some Maya sites; and because it remains puzzling why most of the Maya heartland remained nearly empty of population and failed to recover after the collapse and after re-growth of forests.

With those caveats, it appears to me that one strand consisted of population growth outstripping available resources: a dilemma similar to the one foreseen by Thomas Malthus in 1798 and being played out today in Rwanda (Chapter 10), Haiti (Chapter 11), and elsewhere. As the archaeologist David Webster succintly puts it, "Too many farmers grew too many crops on too much of the landscape." Compoundin that mismatch between population and resources was the second strand: the effects of deforestation and hillside erosion, which caused a decrease in the amount of useable farmland at a time when more rather than less farmland was needed, and possibly exacerbated by an anthropogenic drought resulting from deforestation, by soil nutrient depletion and other soil problems, and by the struggle to prevent bracken ferns from overruning the fields.

The third strand consisted of increased fighting, as more and more people fought over fewer resources. Maya warfare, already endemic, peaked just before the collapse. That is not surprising when one reflects that at least 5,000,000 people, perhaps many more, were crammed into an area smaller than the state of Colorado (104,000 square miles). That warfare would have decreased further the amount of land available for agriculture, by creating no-man's lands between principalities where it was now unsafe to farm. Bringing matters to a head was the strand of climate change. The drought at the time of the Classic collapse was not the first drought that the Maya had lived through, but it was the most severe. At the time of the previous droughts, there were still uninhabited parts of the Maya landscape, and people at a site affected by drought could save themselves by moving to another site. However, by the time of the Classic collapse the landscape was now full, there was no useful unoccupied land in the vicinity on which to begin anew, and the whole population could not be accommodated in the few areas that continued to have reliable water supplies.

As our fifth strand, we have to wonder why the kings and nobles failed to recognize and solve these seemingly obvious problems undermining their society. Their attention was evidently focused on their short-term concerns of enriching themselves, waging wars, erecting monuments, competing with each other, and extracting enough food from the peasants to support all those activities. Like most leaders throughout human history, the Maya kings and nobles did not heed long-term problems, insofar as they perceived them. We shall return to this theme in Chapter 14.

(Jared Diamond: Collapse, pp. 176-177)

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