Collapse: How Societies Choose to Fail or Succeed (26 page)

beaches, for generation after generation, staring out to sea in the hopes of
sighting the canoes that had stopped coming, until even the memory of what a canoe looked like grew dim?

While the details of how human life flickered out on Pitcairn and Hen
derson remain unknown, I can't tear myself free of the mysterious drama.
In my head, I run through alternative endings of the movie, guiding my
speculation by what I know actually did happen to some other isolated soci
eties. When people are trapped together with no possibility of emigration,
enemies can no longer resolve tensions merely by moving apart. Those tensions may have exploded in mass murder, which later nearly did destroy the
colony
of Bounty
mutineers on Pitcairn itself. Murder could also have been driven by food shortage and cannibalism, as happened to the Mangarevans, Easter Islanders, and
—closer to home for Americans—the Donner Party in
California. Perhaps people grown desperate turned to mass suicide, which was recently the choice of 39 members of the Heaven's Gate cult near San Diego, California. Desperation might instead have led to insanity, the fate of some members of the Belgian Antarctic Expedition, whose ship was
trapped by ice for over a year in 1898-1899. Still another catastrophic end
ing could have been starvation, the fate of Japan's garrison stranded on
Wake Island during World War II, and perhaps exacerbated by a drought,
typhoon, tsunami, or other environmental disaster.

Then my mind turns to gentler possible endings of the movie. After a few generations of isolation on Pitcairn or Henderson, everyone in their
microsociety of a hundred or a few dozen people would have been everyone
else's cousin, and it would have become impossible to contract a marriage
not in violation of incest taboos. Hence people may just have grown old to
gether and stopped having children, as happened to California's last surviv
ing Yahi Indians, the famous Ishi and his three companions. If the small
population did ignore incest taboos, the resulting inbreeding may have
caused congenital physical anomalies to proliferate, as exemplified by deaf
ness on Martha's Vineyard Island off Massachusetts or on the remote At
lantic island of Tristan da Cunha.

We may never know which way the movies of Pitcairn and Henderson
actually ended. Regardless of the final details, though, the main outline of the story is clear. The populations of Mangareva, Pitcairn, and Henderson
all inflicted heavy damage on their environments and destroyed many of
the resources necessary for their own lives. Mangareva Islanders were nu
merous enough to survive, albeit under chronically terrifying conditions
and with a drastically reduced standard of living. But from the very begin-

CHAPTER
4

The Ancient Ones: The Anasazi and Their Neighbors

Desert farmers
■ Tree rings Agricultural strategies ■

Chaco's problems and packrats Regional integration
■

Chaco's decline and end Chaco's message
■

O

f the sites of societal collapses considered in this book, the most remote are Pitcairn and Henderson Islands discussed in the last
chapter. At the opposite extreme, the ones closest to home for
Americans are the Anasazi sites of Chaco Culture National Historical Park (
Plates 9, 10) and Mesa Verde National Park, lying in the U.S. Southwest on N
ew Mexico state highway 57 and near U.S. highway 666, respectively, less t
han 600 miles from my home in Los Angeles. Like the Maya cities that will b
e the subject of the next chapter, they and other ancient Native American r
uins are popular tourist attractions that thousands of modern First World citizens visit each year. One of those former southwestern cultures, Mim-b
res, is also a favorite of art collectors because of its beautiful pottery deco-

rated
with geometrical patterns and realistic figures: a unique tradition c
reated by a society numbering barely 4,000 people, and sustained at its p
eak for just a few generations before abruptly disappearing.

I concede that U.S. southwestern societies operated on a much smaller scale than did Maya cities, with populations of thousands rather than mil-
ions. As a result, Maya cities are far more extensive in area, have more lavish
monuments and art, were products of more steeply stratified societies
leaded by kings, and possessed writing. But the Anasazi did manage to con-s
truct in stone the largest and tallest buildings erected in North America
until the Chicago steel girder skyscrapers of the 1880s. Even though the
Anasazi lacked a writing system such as the one that allows us to date Maya
inscriptions to the exact day, we shall see that many U.S. southwestern
structures can still be dated to within a year, thereby enabling archaeologists to
understand the societies' history with much finer time resolution than is
possible for Easter, Pitcairn, and Henderson Islands.

In the U.S. Southwest we are dealing with not just a single culture
and collapse, but with a whole series of them (map, p. 142). Southwestern
cultures that underwent regional collapses, drastic reorganizations, or aban
donments at different locations and different times include Mimbres
around
a.d.
1130; Chaco Canyon, North Black Mesa, and the Virgin Anasazi
in the middle or late 12th century; around 1300, Mesa Verde and the
Kayenta Anasazi; Mogollon around 1400; and possibly as late as the 15th
century, Hohokam, well known for its elaborate system of irrigation agri
culture. While all of those sharp transitions occurred before Columbus's ar
rival in the New World in 1492, the Anasazi did not vanish as people: other
southwestern Native American societies incorporating some of their descendants persist to this day, such as the Hopi and Zuni pueblos. What ac
counts for all those declines or abrupt changes in so many neighboring
societies?

Favorite single-factor explanations invoke environmental damage,
drought, or warfare and cannibalism. Actually, the field of U.S. southwest
ern prehistory is a graveyard for single-factor explanations. Multiple factors
have operated, but they all go back to the fundamental problem that the
U.S. Southwest is a fragile and marginal environment for agriculture
—as is
also much of the world today. It has low and unpredictable rainfall, quickly
exhausted soils, and very low rates of forest regrowth. Environmental prob
lems, especially major droughts and episodes of streambed erosion, tend to recur at intervals much longer than a human lifetime or oral memory span.
Given those severe difficulties, it's impressive that Native Americans in the
Southwest developed such complex farming societies as they did. Testimony
to their success is that most of this area today supports a much sparser population growing their own food than it did in Anasazi times. It was a moving and unforgettable experience for me, while I was driving through
areas of desert dotted with the remains of former Anasazi stone houses,
dams, and irrigation systems, to see a now virtually empty landscape with just the occasional occupied house. The Anasazi collapse and other southwestern collapses offer us not only a gripping story but also an instructive
one for the purposes of this book, illustrating well our themes of human
environmental impact and climate change intersecting, environmental and population problems spilling over into warfare, the strengths but also the
dangers of complex non-self-sufficient societies dependent on imports and
exports, and societies collapsing swiftly after attaining peak population
numbers and power.

Our understanding of southwestern prehistory is detailed because of two
advantages that archaeologists in this area enjoy. One is the packrat midden method that I'll discuss below, which provides us with a virtual time capsule
of the plants growing within a few dozen yards of a midden within a few de
cades of a calculated date. That advantage has allowed paleobotanists to
reconstruct changes in local vegetation. The other advantage allows archaeologists to date building sites to the nearest year by the tree rings of the site's
wood construction beams, instead of having to rely on the radiocarbon
method used by archaeologists elsewhere, with its inevitable errors of 50 to
100 years.

The tree ring method depends on the fact that rainfall and temperature
vary seasonally in the Southwest, so that tree growth rates also vary season
ally, as true at other sites in the temperate zones as well. Hence temperate
zone trees lay down new wood in annual growth rings, unlike tropical rainforest trees whose growth is more nearly continuous. But the Southwest is
better for tree ring studies than most other temperate zone sites, because the dry climate results in excellent preservation of wooden beams from trees felled over a thousand years ago.

Here's how tree ring dating, known to scientists as
dendrochronology
(from the Greek roots
dendron =
tree, and
chronos =
time), works. If you cut
down a tree today, it's straightforward to count the rings inwards, starting
from the tree's outside (corresponding to this year's growth ring), and thereby to state that the 177th ring from the outermost one towards the
center was laid down in the year 2005 minus 177, or 1828. But it's less
straightforward to attach a date to a particular ring in an ancient Anasazi
wooden beam, because at first you don't know in what year the beam was cut. However, the widths of tree growth rings vary from year to year, depending on rain or drought conditions in each year. Hence the sequence of rings in a tree cross-section is like a message in the Morse code formerly
used for sending telegraph messages; dot-dot-dash-dot-dash in the Morse
code, wide-wide-narrow-wide-narrow in a tree ring sequence. Actually, the
ring sequence is even more diagnostic and richer in information than the
Morse code, because trees actually contain rings spanning many different widths, rather than the Morse code's choice between only a dot or a dash.

Tree ring specialists (known as dendrochronologists) proceed by noting the sequence of wider and narrower rings in a tree cut down in a known re
cent year, and also noting the sequence in beams from trees cut down at various unknown times in the past. They then match up and align ring
sequences with the same diagnostic wide/narrow patterns from different

beams. For instance, suppose that this year (2005) you cut down a tree that proves to be 400 years old (400 rings), and that has an especially distinctive sequence of five wide rings, two narrow rings, and six wide rings for the 13 years from 1643 back to 1631. If you find that same distinctive sequence starting seven years from the outermost ring in an old beam of unknown felling date with 332 rings, then you can conclude that the old beam came from a tree cut down in 1650 (seven years after 1643), and that the tree began to grow in the year 1318 (332 years before 1650). You then go on to align that beam, from the tree living between 1318 and 1650, with even older beams, and you similarly try to match up tree ring patterns and find a beam whose pattern shows that it comes from a tree that was cut down after 1318 but began growing before 1318, thereby extending your tree ring record farther back into the past. In that way, dendrochronologists have constructed tree ring records extending back for thousands of years in some parts of the world. Each such record is valid for a geographic area whose extent depends on local weather patterns, because weather and hence tree growth patterns vary with location. For instance, the basic tree ring chronology of the American Southwest applies (with some variation) to the area from northern Mexico to Wyoming.

A bonus of dendrochronology is that the width and substructure of each ring reflect the amount of rain and the season at which the rain fell during that particular year. Thus, tree ring studies also allow one to reconstruct past climate; e.g., a series of wide rings means a wet period, and a series of narrow rings means a drought. Tree rings thereby provide southwestern archaeologists with uniquely exact dating and uniquely detailed year-to-year environmental information.

The first humans to reach the Americas, living as hunter-gatherers, arrived in the U.S. Southwest by 11,000
b.c.
but possibly earlier, as part of the colonization of the New World from Asia by peoples ancestral to modern Native Americans. Agriculture did not develop indigenously in the U.S. Southwest, because of a paucity of domesticable wild plant and animal species. Instead, it arrived from Mexico, where corn, squash, beans, and many other crops were domesticated
—corn arriving by 2000
b.c.,
squash around 800
b.c.,
beans somewhat later, and cotton not until
a.d.
400. People also kept domestic turkeys, about which there is some debate whether they were first domesticated in Mexico and spread to the Southwest, or vice versa, or whether they were domesticated independently in both areas. Originally,

southwestern Native Americans just incorporated some agriculture as part
of their hunter-gatherer lifestyle, as did the modern Apache in the 18th and
19th centuries: the Apache settled down to plant and harvest crops during the growing season, then moved around as hunter-gatherers during the rest of the year. By
a.d.
1, some southwestern Native Americans had already
taken up residence in villages and become primarily dependent on agricul
ture with ditch irrigation. Thereafter, their populations exploded in num
bers and spread over the landscape until the retrenchments beginning around
a.d.
1117.

At least three alternative types of agriculture emerged, all involving dif
ferent solutions to the Southwest's fundamental problem: how to obtain enough water to grow crops in an environment most of which has rainfall
so low and unpredictable that little or no farming is practiced there today.
One of the three solutions consisted of so-called dryland agriculture, which meant relying on rainfall at the higher elevations where there really was enough rain to promote growth of crops in the fields on which the rain fell.
A second solution did not depend on rain falling directly on the field, but
instead was adopted in areas where the water table in the ground reached
close enough to the surface that plant roots could extend down into the wa
ter table. That method was employed in canyon bottoms with intermittent
or permanent streams and a shallow alluvial groundwater table, such as in
Chaco Canyon. The third solution, practiced especially by the Hohokam
and also at Chaco Canyon, consisted of collecting water runoff in ditches or
canals to irrigate fields.

While the methods used in the Southwest to obtain enough water to
grow crops were variants on those three types, people experimented in dif
ferent locations with alternative strategies for applying those methods.
The experiments lasted for almost a thousand years, and many of them succeeded for centuries, but eventually all except one succumbed to environmental problems caused by human impact or climate change. Each al
ternative involved different risks.

One strategy was to live at higher elevations where rainfall was higher, as
did the Mogollon, the people at Mesa Verde, and the people of the early
agricultural phase known as the Pueblo I phase. But that carried the risk
that it is cooler at high than at low elevations, and in an especially cool year
it might be too cold to grow crops at all. An opposite extreme was to farm at
the warmer low elevations, but there the rainfall is insufficient for dryland
agriculture. The Hohokam got around that problem by constructing the most extensive irrigation system in the Americas outside Peru, with hun-

dreds of miles of secondary canals branching off a main canal 12 miles
long, 16 feet deep, and 80 feet wide. But irrigation entailed the risk that hu
man cutting of ditches and canals could lead to sudden heavy water runoff
from rainstorms digging further down into the ditches and canals and in
cising deep channels called arroyos, in which the water level would drop be
low the field level, making irrigation impossible for people without pumps.
Also, irrigation poses the danger that especially heavy rains or floods could
wash away the dams and channels, as may indeed eventually have happened
to the Hohokam.

Another, more conservative, strategy was to plant crops only in areas
with reliable springs and groundwater tables. That was the solution initially
adopted by the Mimbres, and by people in the farming phase known as
Pueblo II at Chaco Canyon. However, it then became dangerously tempting
to expand agriculture, in wet decades with favorable growing conditions, into marginal areas with less reliable springs or groundwater. The popula
tion multiplying in those marginal areas might then find itself unable to
grow crops and starving when the unpredictable climate turned dry again.
That fate actually befell the Mimbres, who started by safely farming the
floodplain and then began to farm adjacent land above the floodplain as
their population came to saturate the fioodplain's capacity to support it.
They got away with their gamble during a wet climate phase, when they
were able to obtain half of their food requirements outside the floodplain. However, when drought conditions returned, that gamble left them with a
population double what the floodplain could support, and Mimbres society
collapsed suddenly under the stress.

Still another solution was to occupy an area for only a few decades, until
the area's soil and game became exhausted, then to move on to another
area. That method worked when people were living at low population densities, so that there were lots of unoccupied areas to which to move, and so that each occupied area could be left unoccupied again for sufficiently long
after occupation that its vegetation and soil nutrients had time to recover.
Most southwestern archaeological sites were indeed inhabited for only a few
decades, even though our attention today is drawn to a few big sites that
were inhabited continuously for several centuries, such as Pueblo Bonito in Chaco Canyon. However, the method of shifting sites after a short occupation became impossible at high population densities, when people filled up the whole landscape and there was nowhere left empty to move to.

One more strategy was to plant crops at many sites even though rainfall
is locally unpredictable, and then to harvest crops at whichever sites did get

enough rain to produce a good harvest, and to redistribute some of that
harvest to the people still living at all the sites that didn't happen to receive enough rain that year. That was one of the solutions eventually adopted at Chaco Canyon. But it involved the risk that redistribution required a com
plex political and social system to integrate activities between different sites,
and that lots of people then ended up starving when that complex system
collapsed.

The remaining strategy was to plant crops and live near permanent or
dependable sources of water, but on landscape benches above the main
floodways, so as to avoid the risk of a heavy flood washing out fields and vil
lages; and to practice a diverse economy, exploiting ecologically diverse
zones, so that each settlement would be self-sufficient. That solution,
adopted by people whose descendants live today in the Southwest's Hopi
and Zuni Pueblos, has succeeded for more than a thousand years. Some
modern Hopis and Zunis, looking at the extravagance of American society
around them, shake their heads and say, "We were here long before you
came, and we expect still to be here long after you too are gone."

All of these alternative solutions face a similar overarching risk: that a
series of good years, with adequate rainfall or with sufficiently shallow
groundwater tables, may result in population growth, resulting in turn in
society becoming increasingly complex and interdependent and no longer
locally self-sufficient. Such a society then cannot cope with, and rebuild it
self after, a series of bad years that a less populous, less interdependent,
more self-sufficient society had previously been able to cope with. As we shall see, precisely that dilemma ended Anasazi settlement of Long House
Valley, and perhaps other areas as well.

The most intensively studied abandonment was of the most spectacular and
largest set of sites, the Anasazi sites in Chaco Canyon of northwestern New
Mexico. Chaco Anasazi society flourished from about
a.d.
600 for more
than five centuries, until it disappeared some time between 1150 and 1200.
It was a complexly organized, geographically extensive, regionally inte
grated society that erected the largest buildings in pre-Columbian North
America. Even more than the barren treeless landscape of Easter Island, the
barren treeless landscape of Chaco Canyon today, with its deep-cut arroyos
and sparse low vegetation of salt-tolerant bushes, astonishes us, because the
canyon is now completely uninhabited except for a few National Park Ser
vice rangers' houses. Why would anyone have built an advanced city in that