Collapse

Pitcairn Island in the South Pacific lies near the extreme eastern edge of Polynesian seafaring society. When the HMS Bounty mutineers escaped to Pitcairn in 1790, they found “temple platforms, petroglyphs, and stone tools giving mute evidence that Pitcairn had formerly supported an ancient Polynesian population” (120). Where did those people go?

That society, and one on the neighboring island of Henderson, disappeared mainly because their chief trading partner, Mangareva Island, suffered an environmental catastrophe.

Mangareva boasts many resources but no materials for good tool-making. Pitcairn has volcanic glass and fine-grained basalt for cutting tools and adzes, but it’s too small for much agriculture; today it supports only 52 residents. Henderson, the largest of the three islands, is a raised coral reef with limited fresh water, little soil, and no tool-making stones, but it supports decent reef fishing and good bird hunting. For centuries a few dozen people lived there in caves.

The three islands traded extensively between AD 1000 and 1450; Mangareva, in turn, exchanged goods with islands further west. Mangarevans cleared their upland forests for cultivation; over the centuries this caused soil erosion, lack of wood for canoes, and finally starvation, cannibalism, and war.

Trade also collapsed—carbon-dated trash pits on Henderson and Pitcairn indicate that trade had ceased by AD 1500—leading to the strangulation of the environmentally stressed Pitcairn and Henderson colonies. In 1606, European visitors saw no one on Henderson, and the 1790 Bounty landing found Pitcairn uninhabited.

Widespread trade between widely dispersed societies occurs all over the interconnected modern world. Ecological stresses affect most of these places, and a breakdown in trade due to environmental failure could prove disastrous, especially for the smaller populations.

Between AD 1130 and 1500, several peoples who lived in the North American Southwest and Northern Mexico—Anasazi, Kayenta, Hohokam, Mimbres, and Mogollon—collapsed, their peoples vanished or dispersed.

Scientists use many clues to reconstruct what happened. One important technique is dendrochronology, the study of tree rings, one per year, which vary in size according to annual rainfall. The resulting pattern of rings can tell researchers when a tree was born and felled, which also determines the age of any building built with the tree’s wood. Tree rings suggest past climate trends: “a series of wide rings means a wet period, and a series of narrow rings means a drought” (139).

The earliest settlers arrived at least 11,000 years ago into a desert region bereft of domesticable plants and animals. Between 2,000 BC and AD 400, corn, squash, beans, and cotton were imported from ancient Mexico, and farming began in earnest in the first century AD. The population flourished for more than a thousand years.

Farming in the arid region relied on three main water-management techniques: high-altitude farming beneath mountain rains, floodplain planting above shallow water tables, and ditch or canal runoff irrigation.

The Hohokam dug ditches off a main canal 12 miles long, but occasional flooding could erode and destroy the system. The Mimbres did well for a time with floodplain agriculture and, during a wet period, in farming areas above the plain. This helped their population grow, but when a dry period set in, many of them starved. Another technique was to plant everywhere and harvest crops where rains turned out to be adequate; Chaco Canyon peoples did this, but it was a complex process, and organizational breakdowns led to starvation.

The Hopi and Zuni practiced floodplain farming on benches above the floodways, with each area being “locally self-sufficient” (43), for a thousand years. Among the region’s earlier societies, good rains brought population increases and greater interdependency, while drought resulted in local trade breakdowns and famine.

Chaco Canyon catches rainfall runoff, contains a range of useful plants and animals, and a long growing season; the Anasazi who lived there from AD 600 to 1200 took advantage of the bounty to develop a complex society with the tallest buildings, at six stories, anywhere north of Mexico until the first Chicago skyscrapers in the late 1800s.

Chaco residents built dams to catch storm runoff, planted near dams that happened to catch some rain, and shared crops with less fortunate neighbors. Carbon-dating of packrat middens—rats’ nests with trash preserved for centuries in the dry climate—shows that piñon pine and juniper were plentiful early in Anasazi history but gone by the end, suggesting that logging had deforested the region by AD 1000. Chaco residents thereafter journeyed to forests 50 miles away to obtain logs.

As the area capital, Chaco Canyon received many goods, including luxuries, from outlying areas but produced little in return. Overpopulated and deforested, its water supply and farmland damaged by arroyo cutting and an extended drought, Chaco and neighboring villages fell into warfare, starvation, and cannibalism. Residents’ scattered bones show signs of being boiled and cracked open for their marrow; dried human feces found nearby contain human muscle protein.

Four of Diamond’s five contributors to societal collapse affected the Anasazi outcome: human-caused environmental stresses included deforestation and misuse of water and soil; climatic change led to drought; trade collapsed; and religious and political factors remained unchanged beyond the breaking point. Only external warfare is absent from the tragedy.

Modern human societies enjoy ecologically expensive, interconnected lifestyles with weaknesses that might cause a collapse not unlike that suffered by the Anasazi.

The Classic Maya civilization spread across modern Yucatan, Guatemala, Belize, and Honduras, flourishing between AD 250 and 760. This large, advanced society then collapsed between AD 760 and 910, leaving major cities, buildings, artwork, and writing largely untouched, with scattered descendants living nearby. The ruins are archaeologically “pure,” and ancient Mayan and colonial documents help piece together the mystery of the civilization’s disappearance.

Four of the five basic causes of collapse figure in the Maya demise: Environmental degradation, droughts, warfare, and a warlike monumental culture all contributed to the eventual failure. Trade items, on the other hand, remained plentiful during and beyond the collapse.

The Mayans lived not in a jungle but in a seasonally wet tropical forest. Droughts were frequent; domesticable plants and animals were few; agricultural techniques were limited; the main crops were corn and beans; and there were no metal tools. The Mayans nonetheless lived densely, with as many as 1,500 people per square mile. Food supply lines were short—everything was carried by humans—and warfare was limited to local battles between cities.

In one southern Maya urban area, Copan, the population expanded from fertile bottomlands up into the nearby, less fertile hills. The population, along with palace construction, peaked between 650 and 800 AD. Hillside crop planting and deforestation caused soil erosion that flooded the bottomlands with infertile soil. By 950 AD, Copan’s population had declined by half; in 1250, no one remained. Most nearby Mayan city-states rose and fell during roughly the same period, though urban centers in the far Northern Yucatan Peninsula with more reliable water supplies lasted longer.

Warfare was chronic in the decades before the collapse. Writing and murals depict wars and conquests; kings were captured and tortured. The worst drought in 7,000 years began in AD 760, peaked in AD 800, and accompanied the collapse. Cities failed in clusters during the worst drought years of AD 760, 810-820, 860, and 910. The southern lowlands lost 99% of their human population, dropping from 3 million to 30,000. Some survivors moved to Yucatan, and a few hundred thousand still occupied the Mayan region at the time of the Spanish conquest.

Petén, a large area south of Yucatan in today’s Guatemala, once central to Mayan society, had only 25,000 residents in 1964. Between then and 1989, more than 300,000 immigrants poured into the region, causing a new cycle of deforestation, and half the forests are now gone. In nearby Honduras, a quarter of the forests have similarly been knocked down.