Moving Up in the World
Archaeologists seek to understand how and when people came
to occupy the Andean and Tibetan plateaus
Mark S. Aldenderfer
S
Mark S. Aldenderfer received a
doctorate in anthropology from
the Pennsylvania State
University in 1977. He taught
at the State University of New
York, Buffalo, and at
Northwestern University
before joining the anthropology
faculty at the University of
California, Santa Barbara, in
1989. Aldenderfer has studied
the early inhabitants of the
Andes for nearly two decades,
and, more recently, he has
begun anthropological investigations focused on the indigenous peoples of the Tibetan
plateau. Address: Department
of Anthropology, University of
California, Santa Barbara,
93106. Internet:
[email protected]
542
tanding some four kilometers above sea
level, the world’s highest plateaus, the Andean altiplano and the Tibetan plateau, appear
bleak, cold and uninviting. These are clearly
tough places to make a living, yet large numbers of people reside there today—and not all
are recent immigrants. Population estimates of
indigenous highlanders are difficult to come
by, but at least six or seven million reside on
the altiplano, and some two million occupy the
Tibetan plateau. Even larger numbers lived on
these highlands in the past. Educated guesses
for the pre-Columbian population in the Andes vary considerably, but it is probable that
from 10 to 12 million people were living at
high elevation in 1492. Estimates for the Tibetan plateau for the early 20th century suggest around six million inhabitants.
These large populations supported impressive cultural achievements. In South America
from 600 to 1100 A.D., the Tiwanaku polity,
with its capital in modern-day Bolivia near
Lake Titicaca, controlled much of the Titicaca
basin and surrounding lowlands on both
flanks of the Andes. And the Tibetan Empire,
with its seat of power in Lhasa, ruled much of
central Asia from the mid-7th through mid-9th
centuries A.D. The empire controlled access to
the lucrative Silk Route (which stretched from
Europe to Japan), sacked the Chinese capital
at Xian in 763 and established Buddhism as the
state religion. Although no central power
emerged on the Tibetan plateau after the collapse of the empire, in the Andes the Tiwanaku
gave way some 350 years later to the Inca.
From their homeland in the Cuzco basin (at an
elevation of some 3,600 meters), the Inca created the largest empire in the New World, which
stretched from northern Ecuador into northwestern Argentina.
These examples make it abundantly clear
that high elevations are not intrinsically inimical to the emergence and expansion of complex societies. Yet high plateaus are generally
harsh and forbidding places. That is why the
world’s earliest civilizations all developed in
American Scientist, Volume 91
lowlands. In the Andes it took almost 3,000
years for cultures on the altiplano to reach a
state of complexity comparable to what could
be found on the coast, and highly advanced
societies flourished at low elevations in China
4,000 years before anything similar emerged to
the west on the Tibetan plateau itself.
The disparity between low- and highelevation environments becomes even more
pronounced when one examines the long archaeological record of prehistoric human migrations. Viewed from this lofty perspective,
these plateaus seem to have become occupied
very late in time—in a sense, almost at the last
minute. Although the data are sketchy and incomplete and, as I shall discuss, controversial,
the high Andes were not visited until 11,000
years ago, and the Tibetan plateau has probably had people treading on it for no more than
25,000 years. Yet humans have lived at low elevations surrounding these plateaus far longer.
Finds of Homo erectus fossils, an early hominid species, are well known from low elevation
areas of China and may date to 800,000 years
ago. Along the southwestern flanks of the Himalayas, stretching from Pakistan to Nepal in a
geological formation known as the Siwalik
Hills, is a series of archeological sites that contain 500,000-year-old hand axes. To the north
of the plateau in central Mongolia, at a cave site
called Tsagaan Agui, recent archaeological research has confirmed a human presence for at
least 125,000 years. Indeed, farther to the north
and west in Siberia, vestiges of human activity
likely date to somewhere between 200,000 and
300,000 years ago. Although it is now rather
clear that these early humans were not the ancestors of today’s populations [see “We Are All
Africans,” page 496], there is no question that
the Tibetan plateau was surrounded by people
long before it was occupied.
Although human movement into the Andean highlands came very late in prehistory
because the colonization of the New World
itself came late—perhaps no earlier than
some 15,000 years ago—the pattern of migra-
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Susal Stebbins
Figure 1. Panoramic view of Jharkot (above), an ancient Nepalese village situated nearly four kilometers above sea level, aptly illustrates that people long ago settled some of
the highest places on Earth. Permanent enclaves at five kilometers’ elevation can be
found in other parts of the Tibetan plateau. At even half that height, lowlanders start to
experience a range of altitude-related ailments. Yet the natives of such high-elevation regions are able to deal with the low oxygen levels, as well as with the rigors of life in
such challenging environments. By far the two largest high-altitude regions (excluding
those in Greenland and Antarctica) are the Tibetan plateau in Asia and the Andean region of South America, which each contain vast areas higher than 2,500 meters in elevation (white areas, left). The author explores the issues of when human beings first
moved into these extreme highlands, why they migrated there and what physiological
adaptations were necessary.
tion is similar to that of Tibet. The earliest
South American sites, such as Monte Verde,
which is located in southern Chile and dates
to about 13,500 years ago, are all found at low
elevations, along both the Atlantic and Pacific coasts. Even the interior of the Amazon
basin, a notoriously difficult habitat for
hunter-gatherers, gave way earlier than the
Andean highlands.
Coping Mechanisms
What explains the tardiness of permanent human occupation and the slow emergence of
complex societies on these high plateaus? One
factor that must be considered in any explanation is that humans evolved at low elevations.
The physiological processes governing the
transmission of oxygen from the alveoli in our
lungs into the hemoglobin in our blood and
thence on to the mitochrondrial powerhouses
in our cells, developed in conditions of sealevel, or near-sea level, air. Living at high altitude thus robs the human body of the abundant oxygen for which it has evolved.
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For most lowlanders, the effects of this hypoxia, which is simply defined as getting less
than the normal amount of oxygen in inspired
air, begin at elevations around 2,500 meters.
Transient hypoxic effects (sometimes known as
“acute mountain sickness”) include headache,
nausea, hyperventilation, dizziness and rapid
fatigue. These obvious symptoms diminish for
most people after 48 hours and pose no longterm threat to health. However, the lasting effects of chronic hypoxia are more subtle: It diminishes work capacity, fertility and cognition,
and it generally slows growth and maturation
in youngsters. Hypoxia also brings on increased exposure to altitude-induced ailments,
such as chronic mountain sickness, and a host
of altitude-aggravated diseases, primarily
those of the pulmonary system.
Another key factor is that high-elevation environments are usually extreme ones. In addition to hypoxia, residents must manage in a
habitat where little grows and where what does
grow has a patchy distribution. The amount
and timing of rainfall are difficult to predict,
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2003
November–December
543
Art Wolfe/Photo Researchers, Inc.
Susal Stebbins
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percentage
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Tibetan
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Figure 2. Tibetan (top left) and Andean (top right) natives show distinctly different physiological adaptations for
high-altitude living. Tibetans cope with low levels of atmospheric oxygen by maintaining higher rates of respiration
(bottom left), whereas Andeans compensate for the thinness of the air with higher concentrations of hemoglobin
in their blood (bottom right). These two populations also differ in a trait that physiologists call “hypoxic ventilatory response,” a natural tendency to increase one’s respiration rate when challenged with low-oxygen conditions.
(Data courtesy of Cynthia M. Beall.)
and tectonic activity often disturbs the land, exposing it to erosion and landslide. Further,
high-elevation environments, even in tropical
latitudes, are usually rather cold places. This
stressor exacerbates the effects of hypoxia and
leads to increased energy demands as well as
increased mortality rates, with many people
succumbing to pulmonary infections. As altitude increases, so does the risk for frostbite, the
onset of which is hastened by the typically
strong winds. Snow blindness is also a significant hazard during the winter. In short, life at
the top of the world can be a real struggle.
To live permanently and thrive at high elevation, a person must have two things: a set of
physiological adaptations to cope with the reduced availability of oxygen and a suite of cultural adaptations to cope with the harsh environment. These include, at a minimum, fire,
effective clothing and a reliable set of tools for
eking out a living. Hunting and gathering peoples, who were the first inhabitants of the high
plateaus, also had to work out patterns of seasonal movement that minimized exposure to
environmental hazards while simultaneously
providing them with sufficient calories.
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American Scientist, Volume 91
Because their basic requirements are the
same, one might expect that Tibetan and Andean peoples are broadly similar in their adaptations to high altitude. In fact, they are not at all
alike. For example, Tibetans and Andean peoples show substantial differences in the way
their bodies cope with chronic hypoxia. Cynthia
M. Beall, an anthropologist at Case Western Reserve University, has identified three traits in
which Tibetans and Andean highlanders differ
significantly: Tibetans can maintain very high
respiratory rates while at rest (a characteristic of
acute hypoxia), whereas Andean natives, as
well as acclimatized lowlanders, have rates similar to those seen in sea-level natives. Tibetans
also show high scores in tests of something
called hypoxic ventilatory response (a reflex to increase respiratory rate under hypoxic conditions), whereas Andean natives exhibit a very
low response. Finally, the concentration of hemoglobin (the protein that carries oxygen) in Tibetan blood is no different from that found in
sea-level residents, whereas Andean natives
show very high hemoglobin concentrations.
Beall’s observations raise some interesting
questions. Does one physiological pattern work
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better than the other? Are these differences
based on natural selection? What role, if any,
has culture played in this process of biological
adaptation? Although there are no definitive answers, various explanations for these differences
have been offered. Some authors posit that the
traits that help these people cope with chronic
hypoxia are merely by-products of long-term
adaptations for greater strength or endurance
at any altitude. Other workers, such as Lorna
G. Moore of the University of Colorado at Denver and her colleagues, have argued that these
traits are indeed evolutionary adaptations to altitude and that the Tibetans have a unique set
because they have lived at high elevation much
longer than have Andean natives. In contrast,
Beall and her co-workers argue that Tibetans
and Andean natives differ because evolution
just happened to take a slightly different course
on two continents and that their present-day
distinctness may just stem from chance differences in genetic makeup of the adventurous
lowlanders who migrated upward and founded
these two populations (although she accepts
that the length of occupation at high elevation
also may have contributed). There are plenty of
ideas and opinions, but very little data with
which to test them.
Digging for Answers
Archaeology can help resolve some of these issues through careful consideration of the antiquity of life at high elevations, the probable
source of the founder populations that occupied the plateaus and the processes by which
humans colonized them.
Unfortunately, knowledge of the prehistory
of the Tibetan plateau is very sketchy. Systematic exploration did not begin there until the
1960s, when the Chinese Academy of Sciences
sent in teams of geologists to conduct surveys
of the local natural resources, during which
they found many archaeological sites at elevations ranging from 3,600 to more than 4,800
meters. It was not until the 1970s, however,
that archaeologists evaluated these sites. None
were excavated, but Chinese archaeologists attempted to gauge their age by matching them
up with sites in eastern and northern Asia that
had been securely dated. The comparisons of
artifacts led some archaeologists to conclude
that the plateau had been occupied for at least
30,000 years. Until recently, Xiao Qaidam, located on the northern fringes of the plateau,
was thought to be the oldest site. Although the
levels that contained human artifacts—simple
stone tools—were not directly dated, correlations with better-known layers nearby suggested the deposit was between 33,000 and
35,000 years old. More recent research, however, indicates that these materials are about
22,000 years old, or possibly younger.
The best current candidate for the oldest site
is called Chusang. It is located in the central
part of the plateau just to the west of Lhasa at
an elevation of 4,200 meters. Two scientists
from the University of Hong Kong, David
Zhang and S. Li, discovered this site in 1995. It
contains 19 human hand- and footprints, impressed into a single layer of mud. Size differences in the prints suggest that both adults and
children made them. The rock with these
prints is called travertine, because it began as a
soft mud full of calcium carbonate. The exact
environment of deposition is unclear from the
observations Zhang and Li recorded, but the
presence of calcium carbonate indicates that
the overlying water must have come from a
Annie Griffiths Belt/Corbis
Figure 3. Evidence that people at least visited the Tibetan plateau before 20,000 years ago—that is, during the height of the last ice age—comes
from the Chusang site near Lhasa, which contains hand- and footprints of both adults and children, impressed into mud that once collected beneath geothermally heated waters and then later solidified, leaving travertine stone (left). Such natural hot springs must indeed have been welcome oases of warmth to ice-age visitors, who could have enjoyed their balmy waters even as snow fell around them—an attractive juxtaposition for people even today, such as for some winter tourists to Yellowstone National Park (right). (Chusang image from Zhang and Li 2002,
courtesy of the American Geophysical Union.)
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2003 November–December 545
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hot spring. The prints were formed sometime
after the mud settled and before the ooze subsequently solidified, forming what is at present
a hard, calcareous deposit.
Zhang and Li also found what they describe
as a hearth near one concentration of prints.
Unfortunately, they unearthed no artifacts of
any kind, but that is not very surprising given
that they did not conduct a systematic search.
Zhang and Li were, however, quite successful
in obtaining ages for quartz crystals extracted
from the travertine and the hearth using optically stimulated luminescence dating, a method
that measures the amount of time that the sediments have remained in the dark (that is, the
time over which they have been buried). Their
study produced dates ranging between 21,000
and 22,000 years before present.
Soon after I learned of this astonishing result, I set my sights on getting to Chusang to
do more work there. I was ready to lead a team
of geologists, paleoclimatologists and archaeologists to Chusang last summer to further
study the site, but authorities halted all travel
to the plateau after the SARS (Severe Acute
Respiratory Syndrome) epidemic struck elsewhere in China. My colleagues and I are hoping for better luck this coming summer, when
we plan to try again.
If Chusang indeed proves to be older than
20,000 years, this site will have a number of
important implications. For most of the 20th
century, many geologists believed that the Tibetan plateau was covered with a thick sheet of
glacial ice during the interval between 22,000
and 18,000 years ago (a period known as the
last glacial maximum). If so, Chusang could
not have been occupied at this time. But more
recent research suggests that, although the last
Zhabu
scraper
> 20,000 years?
4,300 meters
Indian
subcontinent
Zhuluole
scraper
>20,000 years?
4,800 meters
Takla Makan desert
glacial maximum may have been very cold
and probably arid as well, no such massive ice
sheet existed. Glaciers covered the high mountain peaks but did not descend into the valley
floors. Life at Chusang must have been hard,
but it was certainly possible.
Still, getting to the central part of the Tibetan
plateau during the height of the last ice age
would have been very difficult. (It’s tricky
enough now.) So it makes sense to suppose that
people arrived somewhat earlier. From 50,000
to 25,000 years ago, climatic conditions across
the plateau were relatively benign. Geologic evidence shows that the glaciers retreated and
lake levels rose, indicating a significant increase
in precipitation compared with former times. It
is reasonable to infer that temperatures also increased. As these processes unfolded, cold
deserts transformed into steppes. This modest
greening in turn would have led to the expansion in the range and numbers of various large
ungulates native to the plateau. Importantly,
these improved conditions may have ameliorated the extreme aridity of the large basins just
to the north (the Takla Makan and Gobi
deserts), thus making movement onto the
plateau from those areas more feasible.
P. Jeffrey Brantingham of the University of
California, Los Angeles, and his Chinese colleagues Ma Haizhou and Gao Xing propose a
three-step process for the peopling of the
plateau. The first step brought a source population from the low elevation zones north of
the plateau (say, Inner Mongolia) into northwestern China no later than 25,000 years ago
and possibly earlier. The second step moved
these peoples into the eastern Qinghai lakes region (at elevations between 3,000 and 4,000
meters) after 25,000 years ago but before the
Xiao Qaidam
scraper
< 22,000 years
3,100 meters
Tibetan plateau
Chusang
hand- and footprints
∼21,000 years
4,200 meters
Figure 4. Peopling of the Tibetan plateau probably began even as the last ice age intensified. Some early evidence comes from the Chusang site,
where human hand- and footprints appear to have been made more than 20,000 years ago. Other notable early artifacts found include stone
scrapers—tools for transforming animal hides into pieces of clothing, which were needed for protection in such extreme environments.
© 2003 Sigma Xi, The Scientific Research Society. Reproduction
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546 American Scientist, Volume 91
extremes of the last glacial maximum. It is during this second migration that cultural and
physiological adaptations to high elevation
conditions commenced. The third step, movement to the higher central plateau, may have
taken place just before the onset of the last
glacial maximum, perhaps between 23,000 and
22,000 years ago. This view of events is consistent not only with the dates from Chusang but
also with at least one hypothesis about the
source of the founding population of the
plateau: Antonio Torroni of the University of
Pavia and his colleagues use mitochrondrial
DNA evidence to argue that indigenous Tibetans have a north Asian and Siberian origin
of uncertain antiquity.
There’s Llama in Them Thar Hills
The archaeological record for the colonization
of highlands is more complete in the Andes
than on the Tibetan plateau, but the evidence is
not without controversy. Although there continue to be claims that human presence in the
New World has a very deep antiquity, most archaeologists now believe that the South American continent was colonized some 15,000
years ago, or perhaps somewhat earlier, if one
believes the DNA evidence. Widely accepted
as the earliest known site of occupation in the
New World, Monte Verde in southern Chile is
dated to roughly 13,500 years ago. But Monte
Verde is a considerable distance from early
peoples’ point of entry into South America
(through the isthmus of Panama into what is
now northwestern Colombia), so most workers
suppose the initial occupation began a millennium or so earlier. A series of sites ranging in
date from about 13,000 to 11,000 years ago is
found along the Pacific coast of the continent.
Asana
scraper
9,800 years
3,350 meters
Fewer sites have been as well documented
along the Atlantic coast, but some ancient
dwelling places in northeastern Brazil are
thought to be of similar antiquity.
A number of highland sites have been said
to reflect an even earlier human presence in
South America. Among the most controversial
of these is Pikimachay, a naturally sculpted
rock shelter found in the Andean foothills at an
elevation of 2,850 meters. Excavated in the
1970s by the late Richard “Scotty” MacNeish,
former director of the Peabody Museum for
Archaeology in Andover, Massachusetts, the
earliest dates from the site range from 14,000 to
20,000 years ago. Found in its basal levels were
flake tools and the bones of an extinct species
of ground sloth presumed to have been
butchered there. However, the purported artifacts from the earliest levels are made from the
same type of stone that makes up the cave
wall, and most archaeologists who have examined them carefully are not convinced they
show clear signs of purposeful shaping. Further, none of the sloth bones (which produced
the early dates) gave evidence of burning or
modification by human hands, thus leading
most archaeologists to believe the animal
found its way into the rock shelter on its own.
A few other sites, such as Pachamachay,
Telarmachay and Guitarrero Cave, all in the
central Andean highlands, have produced radiocarbon dates in the 12,000-year range, but
the investigators who reported them suggest
they are not reliable and instead argue that the
earliest occupation of these highland sites most
likely took place between 11,500 and 11,000
years ago. If so, humans lived at the base of
the altiplano for at least 2,000 years before
moving up into the highlands.
Amazon
basin
Altiplano
Pacific
Ocean
Tuina
projectile point
∼10,000 years
2,800 meters
Monte Verde
projectile point
∼13,500 years
sea level
Guitarrero Cave
flake tool
∼10,000 years
2,580 meters
Figure 5. Peopling of the Andes took place as the last ice age waned. Monte Verde, the earliest well-documented site in the Americas, gives evidence
of habitation near sea level some 13,500 years ago. Other coastal sites to the north are known to have been occupied not much later, but it took a millennium or two for people venture into the Andean highlands, where they left behind such artifacts as stone projectile points and scrapers.
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2003 November–December 547
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Fletcher & Baylis /Photo Researchers, Inc.
Figure 6. Wild game, such as the vicuna, would have helped to draw early occupants of
the coastal regions into the highlands of South America. While still dwelling in the
lowlands, these people would have grown to depend on such animals, which probably
shifted their ranges to higher elevations as the Ice Age waned and the climate warmed.
population density
(people per square kilometer)
As is the case for Tibet, environmental factors appear to explain in great part why humans did not move into the highlands more
rapidly. After 18,000 years ago, the glaciers that
covered the high mountain peaks of the Andes began to retreat. This process, however,
was slow, and its progress depended on the local topography. In the central Andes, for example, significant deglaciation did not take
place until about 12,000 years ago, whereas in
the Lake Titicaca basin, it happened about
1,000 years earlier. At the time, temperatures
throughout the Andes hovered some five to
eight degrees Celsius colder than today. On the
western flanks of the Andes, snowlines
reached 500 meters below their current position (at 4,800 meters), and plants adapted to
the cold grew well below their modern ranges.
Compared with the Pacific coast, with its abundance of fish and now-extinct land mammals,
these valleys would have had little to offer early hunter-gatherers.
After 12,000 years ago, temperatures continued to increase, but rainfall diminished. By
10,000 years ago, changes in wind circulation
across South America created a rain shadow
on the western flanks of the Andes, leading to
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the formation of the hyperarid Atacama
Desert. Glaciers (here and elsewhere in the
world) melted, raising sea level by more than
100 meters from its lowest point. Inundation
of the coasts would have affected the people
living along them. Fresh water, once abundant,
became scarce and was found only in small
springs or in permanent streams descending
from the mountains. Many animals, especially
large-bodied mammals once common in the
Pleistocene, became extinct. But all was not
bleak. The alpine valleys of South America witnessed a rebirth, as various lowland plants and
animals moved into them. This biological
wealth, combined with the water the valleys
contained, offered lowland hunters and gatherers a new niche into which they could expand, one of considerable potential.
Although the events I have outlined here are
admittedly somewhat speculative, work I did
more than a decade ago at Asana, an archaeological site in southern Peru, provides a good
basis for this reconstruction. The site is located
at an elevation of 3,350 meters and lies approximately 40 kilometers to the west of the altiplano. Although the mouth of the river that
drains this area was occupied as early as 10,500
years ago, people moved into the highlands
only about 9,800 years ago.
The archaeological evidence from the earliest levels at Asana reflects very limited activity,
possibly of bands of hunters or small families
residing at the site for very short periods of
time. These groups probably maintained more
permanent camps farther down the valley.
They would have experienced acute hypoxia
as well as reduced work capacity, thus making
it difficult for them to get very much out of the
time spent at altitude.
This strategy of brief visits soon gave way,
however, probably within a span of about 500
years, to a pattern of longer-term occupancy
and exploitation of highland resources. By 9,300
years ago, not only were larger groups living at
the site, they stayed there longer and performed
a wider range of activities compared with their
predecessors. One of the most common tasks
was the making of high-quality leather clothing, which would have been a necessity as people began living there permanently. There is also
clear evidence that at this time these foragers
began exploring the altiplano to the east, which
stood at even greater elevations.
Some of these pioneers would have discovered that living permanently at altitude was
beneficial, in that it allowed them to acclimatize
and thus increased their work capacity. But
there was a hidden cost too: the higher caloric
demand, which would have been especially
problematic for pregnant or lactating women.
Infant mortality probably rose significantly, at
least until women of child-bearing age made the
requisite biological adaptation to chronic hy-
Figure 7. Demographic analysis of present-day world population shows that regions between 2,200 and 2,300 meters in elevation are quite densely settled—second only to the
coasts. This tendency for people to gravitate to such highlands may reflect the richness
of the volcanic soil that blankets many such locales, or it may demonstrate the desire of
their residents to avoid the heat and mosquito-borne illnesses of tropical lowlands.
Population density does, however, taper off as elevation increases beyond what human physiology can readily accommodate. (Data from Cohen and Small 2002.)
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548 American Scientist, Volume 91
poxia. It seems that this impediment, combined
with the low productivity of the region compared with lower elevations, slowed population
growth in the highlands—until people eventually learned to domesticate plants and animals.
Some archaeologists have speculated that the
domestication of maize brought a second wave
of colonists to parts of the South American highlands sometime around 3,500 years ago.
Waves of Grain
Anthropologists working on the Tibetan
plateau have hypothesized that there, too, the
initial entry was followed by at least one additional migration, this time of village agriculturalists rather than hunting and gathering
peoples. Bing Su of the University of Cincinnati and his colleagues, using analyses of DNA
obtained from the Y chromosome, argue that
the modern inhabitants of the Tibetan plateau
arrived just after 6,000 years ago from a source
in the upper Yellow River basin. They propose
that the plateau became increasingly populated as new communities budded off from established ones—a process stoked by the exploitation of domesticated plants and animals.
Their conclusion has important implications,
because it would substantially shorten the time
available for natural selection to have allowed
these people to adapt to the hypoxic conditions
encountered at elevation. Moreover, if Su’s
model is correct, the length of time Tibetans
have been at altitude is similar to that of Andean natives, which lends support to the notion that the two distinct adaptations to chronic hypoxia have more to do with the nature of
the founding populations than the amount of
time that evolution has had to operate.
Although no cultural adaptation can overcome the effects of chronic hypoxia, it is clear
that the appearance of domesticated plants and
animals on the high plateaus made it possible
for these populations to grow substantially and
for complex societies to emerge during the first
millennium A.D. And what of the present era?
In Peru, many of the young highlanders have
been migrating to the lowlands, particularly to
coastal cites, in huge numbers since the 1970s.
The highlands thus contain an increasing proportion of elderly people, most living in desperate poverty. In Tibet, a third wave of migration, this time of Han Chinese immigrants, has
seriously disrupted traditional ways of life on
the plateau.
There is no question that modern clothing,
improved insulation and building materials,
and access to effective medicines have aided
the modern immigrants (along with many of
the natives), making their lives at high elevation more tolerable. My guess is that of these,
the one that has made the greatest difference is
modern medicine. Antibiotics are accessible in
both Peru and Bolivia, and, to a lesser extent, in
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Tibet, and these have reduced infant mortality
substantially. Improved prenatal care for expectant mothers has also helped, as has better
nutrition.
It is no surprise, then, that many people today are able to thrive at high elevations. But it
is a surprise that these challenging regions
prove to be especially attractive places to live.
Joel E. Cohen of Rockefeller University and
Christopher Small of Columbia University
have shown that although the most densely
populated stratum in the world lies within 100
meters of sea level, second place goes to the
zone between 2,200 and 2,300 meters in elevation. They speculate that this pattern might
have something to do with the desire to avoid
mosquito-borne diseases so prevalent in many
tropical lowlands or with the great fertility of
volcanic soils found in many highland locales.
It would thus seem that dwelling near the top
of the world remains, for one reason or another, an appealing way of life.
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2003
November–December
549