Richard Wrangham

Killer species

Human social behavior varies so much

that our plasticity can sometimes seem
in½nite. But human variation has obvi-
ous limits when we compare ourselves
with our primate relatives. Napoleon
may have claimed that he always had
to give in to his wife, the Empress Jose-
phine, but there are no human societies
that follow the lemur pattern of all males
invariably subordinating themselves to
all females. Nor do women anywhere
entice all their male counterparts in their
community to mate with them every
月, as female chimpanzees do. Just
as other species have their particular so-
cial tendencies, 换句话说, so does
ours. Features characteristic of human
society include social communities com-
posed of individuals who associate at

Richard Wrangham, professor of biological an-
thropology at Harvard University, has studied
chimpanzees in Gombe (with Jane Goodall) 和
in Kibale, as well as vervet monkeys and gelada
baboons. His book “Demonic Males: Apes and
the Origins of Human Violence” (1996) popular-
ized ideas he developed in research focused on the
influence of ecology on the evolution of primate
social behavior. 他曾是该协会的院士
美国学院自 1993.

将要, multilevel ties among communities,
mothers forming mating bonds, coali-
tions of males ½ghting over territory,
等等.

That all humans share some character-
istic social tendencies may be unremark-
able in comparison with other species,
but it provides valuable insight into be-
havioral evolution. In this essay I will
focus on a few features we share with
our closest ape relatives, but that are
otherwise found rarely. 尤其,
we share the tendency for coalitions of
related males to cooperate in defending
a shared territory; and we kill our ene-
mies. These are unusual patterns in oth-
er primates, so the question is why they
should be prominent in humans and our
close kin.

One hypothesis is phylogenetic iner-
tia, the nonadaptive retention of an an-
cestral trait. Phylogenetic inertia is a
possibility whenever closely related spe-
cies behave alike. 例如, horses
and zebras both live in groups of unre-
lated females and single stallions within
larger herds. Breeding wolves and coy-
otes live as isolated monogamous pairs
aided by nonbreeding helpers. 男性
hornbills of many different species
imprison their mating partners in a se-
cluded breeding hole. There are many
such examples of social systems corre-

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理查德
Wrangham
在
人类
自然

lated with phylogeny, and in theory
these could result from species failing to
adapt their behavior to new circum-
姿态.

However attractive the notion of phy-

logenetic inertia might seem, it suffers
from the problem of explaining why
adaptive changes in social behavior
should be constrained. The hypothesis
of adaptive socioecology is therefore a
strong a priori alternative to phylogenet-
ic inertia. Adaptive socioecology posits
that a similar lifestyle is the key to simi-
lar behavior among closely related spe-
化学系, whether it be grass-eating for hors-
es and zebras, den-living for wolves and
coyotes, or a shortage of suitable nesting
holes for different species of hornbills.
Adaptive socioecology rests on the no-
tion that social systems can change rap-
idly in response to a novel ecology.

Baboons offer a particularly tidy ex-
ample of adaptive socioecology, 因为
even within a single species genetically
based differences in psychology have
evolved in apparent response to a specif-
ic ecological change. East Africa’s olive
baboons live in lush grasslands where
the abundance of food permits large, 共-
operative groups of female kin that aid
each other in competition against other
女性. Too large to be monopolized by
a single male, a group generally includes
ten or more unrelated males that join
as adolescents. Female olive baboons re-
spond to the plethora of males by mating
widely within the group, thereby garner-
ing protection for their offspring from
the numerous possible fathers. A rich
food supply thus promotes large, 多-
male groups of promiscuous and kin-
bonded females.

Hamadryas baboons, 相比之下, oc-
cupy semideserts in northeast Africa and
Arabia. They resemble olive baboons
closely, being only marginally smaller,
with somewhat more colorful males. 在

their dry habitat, food is so sparse that in
bad seasons the large groups fragment
by day in search of forage. But females
can’t survive without a defending male,
so each stays in a small subgroup with a
单身男性, to whom she becomes faith-
fully bonded and whom she allows to
herd her when other males are near. 到
prevent other males from stealing their
females when the subgroups reunite at
sleeping sites, males form defensive alli-
ances with each other. A poor food sup-
ply thus leads to small families of acqui-
escent female hamadryas attached to a
network of bonded males.

The contrasting baboon social pat-
terns conform to the respective ecologi-
cal pressures. These differences could
in theory emerge merely as the baboons’
developmental response to their imme-
diate environments, but there is evi-
dence of strong genetic influence. 因此
even after many generations in captivity,
baboons of the two subspecies form the
same kinds of social groups as their wild
祖先. The same differentiation is
dramatically echoed among naturally
occurring hybrids in Ethiopia, for which
physical features and behavior are corre-
lated. Females that look more like olive
baboons, 例如, strongly resist
male efforts to herd them. 相比之下,
those that look more like hamadryas
readily accept a male’s herding. Differ-
ences in serotonin levels between males
of the two subspecies of baboons con-
form to the different patterns of aggres-
锡安.

Olive and hamadryas baboons differ-
entiated from each other around three
hundred thousand years ago. 即使-
out any notable anatomical evolution,
所以, three hundred thousand years
and a changed ecology are enough for
radical adaptation in social behavior, 在-
cluding patterns of grouping, kin rela-
系统蒸发散, and feeding competition.

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Killer
物种

为什么, 然后, should humans be in the
least similar to our cousin apes? 奇姆-
panzees and bonobos are separated from
humans not only by ½ve to six million
年, but by enormous changes in ecol-
ogy and ability, including raw biological
differences in diet, locomotion, and sex-
uality, as well as by the re½ned influ-
ences of language and culture. Against
this background, signi½cant social sim-
ilarities with our cousin apes are puz-
zling. While phylogenetic inertia is an
explanation of last resort, adaptive so-
cioecology is at ½rst glance improbable.
正如我们将看到的, 然而, hidden ecologi-
cal similarities suggest that contrary to
the apparent differences between hu-
mans and other apes, our shared social
features derive from parallel ecological
pressures.

Though human hunter-gatherers (还

called foragers) offer the most appropri-
ate comparison with other species, 他们的
lifestyle and social relations differ about
as much from those of our cousin apes as
any other people’s. Foragers dig for roots
and collect fruits, hunt large game, cook
their food, construct simple housing,
and defend themselves with spears or
other weapons. They tend to occupy
temporary camps for several weeks at a
时间, housing a group of perhaps twenty
to forty people, and they relocate these
camps when the women ½nd it hard to
get enough food within a reasonable
day’s walk. The members of a camp are
part of a larger social community that
might include a few hundred or even a
thousand or more people. At certain
times of the year this community gath-
ers for a few days, when feasts and cere-
monies allow social relationships to be
re-formed across the wider network of
the tribe. And as is true for every other
human society, cultural rules pervade
life among such communities. None of
this is very ape-like.

Chimpanzees and bonobos are the
species of apes that are closest to hu-
芒斯. Both are quadrupedal, forest-liv-
ing fruit-eaters that climb for most of
their food, sleep in trees exposed to the
rain, and use only the simplest tools
(some populations use none). 他们的
communities are limited to the set of
individuals that live suf½ciently close
that they might meet by chance. 这些
communities are formed around a core
of related males, and there are no bonds
among mates.

Yet different as humans and these apes

是, all three species live in social com-
munities with no ½xed associations of
individuals other than those between
mothers and their dependent offspring
–a rare trait in the context of most other
primates. 因此, during the day,
individuals of these species can decide
for themselves where to go. 在实践中,
among hunter-gatherers most women
forage every day in the company of oth-
er women from their temporary camp,
much as most male chimpanzees spend
the day in the company of chosen allies.
But in both cases, there are options. A
woman might choose to make a tryst,
stay in the camp, or walk alone. A male
chimpanzee might equally well opt to
travel alone for hours or days at a time.
Such individual choice within a de-
½ned social network occurs in only one
other group of primates: the atelines,
South American monkeys distantly re-
lated to apes. In addition to community
组织, those species share a sec-
ond rare similarity with humans, 奇姆-
潘吉斯, and bonobos: their males form
coalitions to defend territory.

There are other ways in which the
atelines (spider monkeys, woolly mon-
keys, and muriqui) are the most ape-like
group of monkeys: their large size rela-
tive to other South American monkeys,
relatively ef½cient travel, mobile shoul-
德斯, and diet of ripe fruit and soft

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理查德
Wrangham
在
人类
自然

树叶. It has therefore been suggested
that resemblances between the social
behavior of atelines and that of the apes
have resulted from parallel adaptations
for harvesting ripe fruit, a resource that
induces intense feeding competition, 在-
dependent travel, and territorial de-
fense.1 In line with this suggestion, 这
protean grouping patterns of humans
may be similarly derived from an evolu-
tionary commitment to high-quality
foods.

Whatever its precise cause, com-

bination of social communities with
small and frequently changing sub-
groups appears to be an important pre-
condition for one of the most striking
similarities between humans and any
other primates: the territorial aggression
observed in humans and chimpanzees
alike.

Warfare is often de½ned in a way that
suggests it is unique to humans, for in-
姿态, as an interaction involving cul-
turally sanctioned plans or weapons or
organized ½ghting between large groups.
But of course the behavior that underlies
human warfare is not unique, 作为
chimpanzee case makes clear.

Most encounters between chimpan-

zee communities involve males. 那里
can be as many as thirty-½ve males in
a community, but the average is ten to
twelve, and most parties (temporary
subgroups) have about half that number.
Interactions with neighboring commu-
nities are never friendly and are often
dangerous.

But even so, males sometimes seek out
opportunities to engage with neighbors.
They routinely conduct border patrols

1 Colin A. Chapman, Richard Wrangham, 和
Lauren J. Chapman, “Ecological Constraints on
Group Size: An Analysis of Spider Monkey and
Chimpanzee Subgroups,” Behavioral Ecology and
Sociobiology 36 (1995): 59–70.

and may penetrate beyond the zone of
relative safety, looking carefully as they
去. Sometimes they climb a tree and face
the neighboring range, as if listening for
rivals. Occasionally they make deep
invasions.

Most encounters that result from
these behaviors happen by chance
when nearby parties surprise each other
at close range–a few hundred yards, 说.
Calls from strangers prompt immediate
tension. Sometimes the listeners briefly
freeze, but more often they let out a vol-
ley of shouts and quickly move. If they
are numerous, they advance. 如果不,
they retreat toward the heart of their
territory.2

But when they meet at close range and

the numbers of males on each side are
similar they’re more likely to stand their
地面. 通常, chimpanzees in the
battleground hurtle unpredictably
through the brush, pausing after each
rush to look and listen tensely around,
often standing bipedal with one hand
on a small tree. For them one decision
might be a matter of success or death.
Their pauses allow them to gauge who’s
在哪里, to ½nd an ally, or to see uncer-
tainty in the enemy. After a stop, 独自的
or in a small tight group of two or three,
they charge off on a new run across the
battle area. Occasionally one of them
gets hit by a passing rusher, but mostly
the chimpanzees from each community
charge backwards and forwards from
safe spots as each side tries to frighten
the other into retreat. The air is thick

2 Michael L. Wilson, Marc D. Hauser, 和
Richard W. Wrangham, “Does Participation
in Intergroup Conflict Depend on Numerical
Assessment, Range Location, or Rank for Wild
Chimpanzees?” Animal Behaviour 61 (2001):
1203–1216, describe playback experiments
showing that when a call is heard from a single
stranger, chimpanzees move forward only if
there are at least three males in the listening
派对, and that otherwise they retreat.

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Killer
物种

with screams and emotion. It’s hard to
tell exactly what’s happening; it’s dif½-
cult even to identify the males in the me-
lee of speed and power and fully erected
hair. Their screams and barks can go on
with hardly a pause for forty-½ve min-
utes.

到底, the party with fewer males
generally retreats. The result can be im-
重要的. For several weeks, the losing
community tends to avoid an area that
would otherwise have provided access
to a preferred food; this could mean the
difference between a few weeks of eating
from a rich fruit crop, and being forced
onto a poor diet that causes delayed re-
sponse and threatens infant survival.

Of more immediate importance, 这些
battles sometimes lead to a lone partici-
pant being caught by several of his ri-
vals. The result tends to be remarkably
lopsided. While the aggressors are un-
likely even to be scratched, the victim
may be killed on the spot, or bruised,
bitten, and torn so badly that he survives
for only a few days or weeks. 相同
result can follow from border patrols
or deep invasions. Overwhelming num-
bers mean the attackers are safe. 一些
males each hold a hand or foot of the ri-
val. The immobilized victim can then be
damaged at will.

Observations from ½ve study sites
now allow the ½rst rough estimates of
death rates from intergroup killing
among chimpanzees. 之间 1963
(when we have Jane Goodall’s ½rst de-
mographic data from Gombe) 和 2002,
a total of about 145 data-years of obser-
vation were logged across the ½ve long-
term sites. During that time, forty-six
intercommunity kills were observed or
suspected. Thirty-one involved mem-
bers of the study communities (twenty-
four adult males, one adult female, six
婴儿). When the number of chimpan-
zees in each community is taken into

帐户, these ½gures yield a median
death rate from intergroup aggression of
140 每 100,000, which rises to 356 每
100,000 if we include suspected cases in
addition to those observed or con½dent-
ly inferred.3

The chimpanzee data resemble death
rates from war among traditional subsis-
tence societies. 因此, based on a world-
wide compilation by Lawrence Keeley,
Michael Wilson and I have assembled
demographic data for thirty-two po-
litically independent peoples. 这些
include twelve hunter-gatherer and
twenty gardening or farming cultures.
For hunter-gatherers, annual war death
rates averaged 165 每 100,000, 关于
the same as the intergroup killing rate
for chimpanzees. For the subsistence
farmers, the toll rose to a startling 595
每 100,000, somewhat above the up-
per estimate for chimpanzees (356
每 100,000).4 The sampled cultures
range from relatively peaceful people
such as the Semai of Malaysia to the
famously dangerous Dani of New Guin-
ea, among whom at least 28 的百分比
men’s deaths, 和 2 percent of women’s,
occurred in war.5 Understanding why
there is such a range is an important
challenge for the future. For the mo-
蒙特, 然而, we can conclude that

3 Rates are calculated from data presented in
Michael L. Wilson and Richard W. Wrangham,
“Intergroup Relations in Chimpanzees,“ 年度的
Review of Anthropology 32 (2003): 363–392. 为了
adult males as a separate class, the equivalent
rates are between 0.38 和 1.30 percent per
年.

4 劳伦斯·H. Keeley, War Before Civilization
(纽约: 牛津大学出版社, 1996).

5 Karl G. Heider, The Dugum Dani: A Papuan
Culture in the Highlands of West New Guinea
(芝加哥: Aldine Publishing Company, 1970),
128, recorded for Dani living in the Grand Val-
ley of Balim River in the central highlands of
western New Guinea.

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理查德
Wrangham
在
人类
自然

death rates from intergroup aggression
among small independent communities
are broadly similar for humans and
黑猩猩.

Shockingly, death rates in the modern

era tend to be lower even when periods
of major war are included. During the
二十世纪, 例如, 格尔-
许多, 俄罗斯, and Japan each experi-
enced rates of war deaths that were less
than half the average hunter-gatherer
速度. The contrast reflects a difference in
the practice of war between prestate and
state societies. In prestate societies all
men are warriors, and all women are vul-
nerable. In state societies, 相比之下,
fewer people are directly exposed to vio-
伦斯 (even though civilians and chil-
dren often suffer worse casualties than
the military) because armies ½ght on
behalf of the larger group.6

There’s only one other mammal
whose intergroup killing has been ob-
served frequently enough to have been
calculated. The discovery would have
been a surprise to Konrad Lorenz, A
founding father of ethology. Lorenz
thought wolves would not kill wolves,
because he saw captive dominants treat-
ing helpless subordinates in a kindly
方式. So he argued that wolves must
have been selected for inhibition. 他是
right in one sense: within social groups,
wolves normally control their emotions
出色地. But Lorenz didn’t know about
wolves in the wild, where food is scarce
and every group is surrounded by its
neighbors.

Wolves of neighboring groups don’t

hold back. David Mech and his col-
leagues studied packs in the glacial up-
lands of Alaska’s Denali National Park,

6 Death rates in the twentieth century were
presented by Keeley, War Before Civilization.
Carolyn Nordstrom, “Deadly Myths of Aggres-
锡安,” Aggressive Behavior 24 (1998): 147–159.

代达罗斯瀑布 2004

an area they considered to be free of hu-
man influences. Based on twenty-two
killings in at least seventeen packs, 他们
estimated that 39 到 65 percent of adult
wolves were killed by other packs. 我们
can expect variation in such rates across
人口, but at least in Minnesota a
similar ½gure emerged: 43 的百分比
wolves not killed by humans were killed
by other wolves.7

These data were presented as percent-
ages of deaths from violence, 而不是
as an annual death rate. Human data
have sometimes been compiled in the
same way, and show that only the most
extreme of human cultures match the
killing rate of wolves. The highest hu-
man death rate from violence has been
recorded in eastern Ecuador, where an-
thropologist James Yost and colleagues
collected data on causes of death for
Waorani horticulturalists living in dis-
persed villages of less than a hundred
人们. Based on 551 deaths, they found
that homicide took the lives of 49 每-
cent of women and 64 percent of men,
close to the ½gure for Denali wolves.8

Other prestate societies show slightly
lower ½gures. More such data have been
collected from highland New Guinea
than from any other part of the world,
because many of the people living there
continued to practice local war until re-
cently. These people include the Tauna

7 L. David Mech, Layne G. Adams, 托马斯·J.
Meier, 约翰·W. 伯奇, and Bruce W. 戴尔, 这
Wolves of Denali (明尼阿波利斯: 大学
Minnesota Press, 1998).

8 詹姆斯·A. Yost and Patricia M. Kelley, “Shot-
枪, Blowguns, and Spears: The Analysis
of Technological Ef½ciency,” in Raymond B.
Hames and William T. Vickers, 编辑。, Adaptive
Responses of Native Amazonians (纽约:
学术出版社, 1983), 189–224. The recorded
deaths include an unrecorded proportion of
killings within villages, so these ½gures do not
correspond exactly to the wolf data.

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Killer
物种

Awa, 和 16 percent of women and 30
percent of men (的 206 deaths) 垂死
from homicide; the Usurufa, 和 12 每-
cent of women and 32 percent of men
(的 514 deaths); the Mae Enga, 和
或许 2 到 3 percent of women and 35
percent of men (的 261 deaths); 和
Huli, 和 1 percent of women and 20
percent of men (的 769 deaths).

For hunter-gatherers, fewer data are
可用的, but the picture is as expected
from the annual kill rate. Homicides
发生, but at lower rates than among
horticultural farmers.9 There are the
Aché of Paraguay, among whom homi-
cide has been responsible for the deaths
的 14 percent of women and 15 百分
of men (的 115 deaths); the Hiwi of Ven-
ezuela, 和 17 percent of women and 14
percent of men (的 124 deaths); 和
Agta of the Philippines, 和 3 百分
of women and 14 percent of men (的 78
deaths).

The point about these ½gures isn’t to
claim any particular numerical averages.
It’s merely to say that with chimpanzees,
wolves, and humans the big picture is
consistent: in typical populations of
these three species, it can be mortally
dangerous to meet the neighbors.

That’s why they all have war zones.

War zones are the border areas where

territories abut, danger lurks, 和派对
rarely go. Low rates of foraging mean
that war zones can become lands of
plenty–rich in tempting resources.

The Upper Missouri War Zone, a cor-
ridor ½ve hundred kilometers long and
two hundred forty kilometers wide, 曾是
a focal area for the intertribal aggression
of numerous indigenous groups, 包括-

ing the Nez Perce, Crow, and Shoshone.
Lewis and Clark described the presence
there of “immence [原文如此] quantities of
buffalo in every direction”;10 the herbi-
vores bene½ted from the low human
predation pressure resulting from the
dangers of hunting in these contested
ranges. So the feared war zone became
a game sink. Territorial tension some-
times works the same way today. 这
Demilitarized Zone (dmz) separating
North and South Korea is so empty of
people that it has particularly high bio-
diversity, and supports large populations
of rare and endangered species extinct
on the rest of the Korean peninsula.
(Conservationists should be worried
about the prospect of peace. When peace
came to the Upper Missouri War Zone,
prey animals were hunted to extinction.)
War zones occurred among hunter-

gatherers also. Anthropologist Bion
Grif½n reports, 例如, 那
Agta of the Philippines knew where the
danger lay. “Hunters are especially aware
of the chance of illegal trespassers and
assume that they may be bent on raid-
英,” Grif½n writes. “In the remotest
forest hunting zones, where hunters
from more than one dialect group may
范围, precautions are taken and one
would seldom hunt alone.”11

In Australia, expeditions outside the

core of the territory were likewise
viewed as dangerous: “The red ochre
gathering expeditions . . . were normally
all-male parties, and although cordial
relationships between groups were

10 Paul S. Martin and Christine R. Szuter,
“War Zones and Game Sinks in Lewis and
Clark’s West,” Conservation Biology 13 (1999):
36–45.

9 Bruce M. Knauft, “Violence and Sociality
in Human Evolution,” Current Anthropology 32
(1991): 391–428, has stressed the evidence that
rates of war are higher among horticulturalists
than among hunter-gatherers.

11 磷. Bion Grif½n, “Forager Resource and Land
Use in the Humid Tropics: The Agta of North-
eastern Luzon, the Philippines,” in Carmel
Schrire, 编辑。, Past and Present in Hunter-Gatherer
学习 (纽约: 学术出版社, 1984), 106.

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理查德
Wrangham
在
人类
自然

寻求的, ½ghting appears to have been a
common hazard faced by traveling par-
领带. One entire party, with the exception
of one man, is recorded as having been
ambushed and killed in about 1870,
whilst in about 1874 all but one of a
group of 30 men were ‘entombed in the
excavations.’”12

在黑猩猩中, evidence of a
game sink in war zones comes from the
group size of their favorite prey species,
red colobus monkeys. Groups averaged
46 percent smaller in the core of the ter-
ritory than in the border area, 根据
to primatologist Craig Stanford. 他
attributed the difference to the lower
hunting pressure in the border areas,
where chimpanzees feared to go.

同时, David Mech describes
how except during periods of extreme
food shortage, the threat of encounter-
ing hostile neighbors keeps packs of
wolves out of border areas. White-tailed
deer therefore occur at particularly high
density in the zones of wolf-pack territo-
rial overlap. Mech believes that these
war-zone populations of deer are critical
for the long-term relationship between
predator and prey, since they provide the
stock for recolonizing the over-hunted
areas in the core of the wolf territories.
Wolf war zones, 换句话说, provide
conservation areas rather in the style of
the Korean dmz.

It’s not the abutment of territories
that makes a war zone. Redtail monkeys
in Kibale also live within territories, 但
they do not kill members of neighboring
communities and they do not avoid the
territorial borders. They use the territory
完全, right up to the border, and merely

12 The quotation is from R. G. Kimber,
“Hunter-Gatherer Demography: The Recent
Past in Central Australia,” in Betty Meehan
and Neville White, 编辑。, Hunter-Gatherer De-
mography Past and Present (悉尼: 大学
of Sydney Press, 1990), 160–170.

defend their ranges with chases when
they meet neighbors. What makes a war
zone is not a territory, but the risk of
being victimized at its edge.

War zones also aren’t known among

bonobos, 或者, for that matter, 之中
most primates or most mammals or
most animals. In the great majority of
物种, territorial encounters involve
展示, chases, and occasional grap-
pling, but not outright killing. 有
only a select few species whose territori-
al boundaries are places of death and
avoidance. The question is why this
selection should include chimpanzees,
wolves, and humans.

A strong evolutionary rationale for

killing derives from the harsh logic of
natural selection. Every homicide shifts
the power balance in favor of the killers.
So the killers have an increased chance
of outnumbering their opponents in
future territorial battles, 因此
of winning them. Bigger territories mean
more food, and therefore more babies.
This unpleasant formula implies that
killing is favored by two conditions. 它
pays whenever resource competition is
激烈的, and whenever killing can be car-
ried out at low risk to the aggressors.

All animals face resource competition.

In the wild, 例如, female chim-
panzees lose weight during poor seasons
and are often so short of food that they
must wait for an abundant fruiting sea-
son before they can conceive. All hunter-
gatherer populations show similar evi-
dence of intermittent food scarcity, 这样的
as reduced growth during poor seasons.
Persistent food shortages suggest that

a larger territory will always pay, 和
long-term data from Gombe con½rm it.
During two decades the territory of the
Kasekela chimpanzee community varied
in size. Shifts in the balance of power
with neighboring communities may

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Killer
物种

have been responsible for these oscilla-
系统蒸发散. When the territory was small, 这
chimpanzees had inadequate food. Indi-
viduals lost body weight and tended to
travel in the small parties typical of peri-
ods of low food supply. Females then
had long intervals between births, 和
offspring survival was low. 当。。。的时候
territory was larger, everything changed.
Male efforts at expanding the territory
led to gains for both sexes. With a better
food supply, all adults gained weight,
females reproduced faster, 和
young survived better.13

The Gombe study nicely shows the
importance of a larger territory. 但它
doesn’t show anything special about the
killer species. Any territory-holding
group can be expected to fare better if its
neighbors’ power declines, allowing its
territory to expand. By the same process
seen in Gombe, a group of any species
that gets a larger territory can be expect-
ed to have improved food and better
再生产. This principle should
apply as much to bonobos and redtail
monkeys as to chimpanzees, wolves, 和
人类. But bonobos and monkeys
don’t kill.

So resource competition is a necessary

condition for war-zone killing, but it’s
not enough on its own. 第二个骗局-
dition is the suf½cient one. Killing must
be cheap.

The special feature of the killer species

is that when parties from neighboring
territories meet, there is sometimes an
imbalance of power so great that one
party can kill a victim without any
signi½cant risk of any of them getting
hurt themselves. For chimpanzees and

13 Jennifer M. 威廉姆斯, Anne E. Pusey, 约翰
V. Carlis, 乙. 磷. Farm, and Jane Goodall, “Fe-
male Competition and Male Territorial Behav-
ior Influence Female Chimpanzees’ Ranging
Patterns,” Animal Behaviour 63 (2002): 347–
360.

wolves, the imbalances of power come
entirely from their protean grouping
图案. For hunter-gatherers, 相同
applies, but there is an extra twist from
human inventiveness. For modern hu-
芒斯, imbalances of power come not
only from being able to form a larger
subgroup than the enemy’s, 但是也
from striking the ½rst lethal blow–
such as by throwing a spear, flaming a
hut, or flying an airplane into a building.
在黑猩猩中, the most likely

victims of homicide are adults found
alone or immediately abandoned by
their friends after being cornered by
members of a hostile community.
Among wolves, the evidence is less di-
直角, 但 90 percent of kills in Denali oc-
curred in winter. 当时, the proba-
bility of a lone individual meeting a par-
ty of at least three other wolves is forty
times higher than in the summer.

Support for the supposed importance

of power imbalances comes from the
species that don’t kill. Bonobos and
monkeys live in relatively stable groups,
with individuals rarely in parties so
small that they might be overwhelmed
by neighbors. Those species have diets
that allow parties the luxury of perma-
nent association.

But among humans, power imbalances

are routine in intercommunity conflict,
and the predominant tactic of war for
small-scale societies is unambiguous.
It’s hit-and-run or ambush. Anthropolo-
gist A. 右. Radcliffe-Brown recorded the
attitude of the Andaman Islanders,
hunter-gatherers living east of India.
“The whole art of ½ghting,” he wrote,
“was to come upon your enemies by sur-
prise, kill one or two of them and then
retreat . . . . They would not venture to
attack the enemy’s camp unless they
were certain of taking it by surprise . . . .
If they met with any serious resistance
or lost one of their own number, 他们

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理查德
Wrangham
在
人类
自然

would immediately retire. Though the
aim of the attacking party was to kill the
男人, it often happened that women or
children were killed.”14

Similar tactics have been described for

hunter-gatherers around the world. 在
澳大利亚, Walbiri men who surprised
enemy camps were said to have killed or
driven off the enemy males, and to have
carried away any women they could ½nd.
In the Arctic, 相比之下, raiders would
normally kill everyone, though they
might spare young girls. Raids typically
involved ½fteen to twenty men, 和
could take ten days to complete.15

That hunter-gatherers would have
raided each other may seem surprising
in view of the reputation of forager soci-
eties like the Kalahari Bushmen for liv-
ing peacefully. Scrutiny of early records
of contact with hunter-gatherers, 如何-
曾经, shows widespread evidence of
primitive violence, even in the Kalahari.
And material culture supports the pic-
真实. Archaeologist Steven LeBlanc has
recently drawn attention to the shields
of Eskimos that attest to the occurrence
of battles. Australian Aborigines also
had shields as well as weapons used ex-
clusively for warfare, such as a hooked
boomerang and a heavy spear. Both in
the Arctic and in Australia there is clear
historical evidence for a combination of
raids and battles.16

The principle that underlies the may-
hem is simple, 然后. When the killing is

14 A. 右. Radcliffe-Brown, The Andaman Island-
呃: A Study in Social Anthropology (剑桥:
剑桥大学出版社, 1948), 85.

15 Azar Gat, “The Human Motivational Com-
丛: Evolutionary Theory and the Causes of
Hunter-Gatherer Fighting, 第一部分: Primary
Somatic and Reproductive Causes,” Anthropo-
logical Quarterly 73 (2000): 20–34.

16 Steven A. LeBlanc, Constant Battles (新的
约克: 英石. 马丁出版社, 2003).

便宜的, kill. In any particular instance it
may or may not lead to a bigger territory,
but from the perspective of natural se-
lection, the speci½c case is less impor-
tant than the average bene½t. The inte-
grating effect of selective pressures on
emotional systems requires only that
killing should lead to bene½ts suf½cient-
ly often. Just as the ½rst male ½g wasp
that emerges from pupation will imme-
diately attempt to kill any other males he
½nds in the same ½g, so the defenders of
territory bene½t by taking advantage of
机会. The killers don’t have to
think through the logic. They may think
of their action as revenge, or placating
the gods, or a rite of manhood–or they
may not think about it at all. They may
do it because it’s exciting, as seems the
case for chimpanzees. The rationale
doesn’t matter to natural selection.17
What matters, 它似乎, is that in fu-
ture battles the neighbors will have one
less warrior. So those who killed will be-
come a little more powerful as a result.

为什么, 然后, do humans, 黑猩猩,

and wolves share the unusual practice of
deliberately and frequently killing neigh-
bors? In each species the violence makes
感觉. Protean grouping patterns allow
individuals to attack only when they
have overwhelming power. Such tactical
success allows them to kill safely and
cheaply, and thereby win a likely in-
crease in resources over the succeeding
months or years. Killing thus emerges as
a consequence of having territories, 迪斯-
persed groups, and unpredictable power
关系. These driving variables, 在
转动, appear to result from ecological
adaptations, whether to a scattered fruit
supply or to the challenges of hunting

17 Klaus Reinhold, “Influence of Male Related-
ness on Lethal Combat in Fig Wasps: A Theo-
retical Analysis,” Proceedings of the Royal Society
of London B 270 (2003): 1171–1175.

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vertebrate prey. 其含义是
because of our particular evolutionary
ecology, natural selection has favored in
the brains of humans, 黑猩猩, 和
wolves a tendency to take advantage of
opportunities to kill enemies.

This doesn’t condemn us to be violent
一般来说. 的确, within our communi-
ties humans are markedly less violent
than most other primates, and in some
ways humans are specially peaceful. 也不
does it mean that intergroup aggression
is inevitable: 相当, it predicts little vio-
lence when power is balanced between
neighboring communities. 也不, 再次,
does it mean that gang attacks on mem-
bers of other tribes or religions or clubs
or countries are necessarily adaptive: 在
evolutionary terms, they may or may not
是. Nor does it mean that women are
incapable of violence, or are inherently
less aggressive than men: it suggests in-
stead why the circumstances that favor
aggression are not identical for men and
女性.

What it does imply, 然而, 就是它
selection has favored a human tendency
to identify enemies, draw moral divides,
and exploit weaknesses pitilessly across
边界. 因此, our species re-
mains specially predisposed to certain
types of violent emotion. That selection
operated in the context of a hunter-gath-
erer world that has all but disappeared.
But if its legacy is that we are biological-
ly prepared by natural selection to be
killers, an understanding of the neural
basis of intergroup violence should be a
research priority.

Killer
物种

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35
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