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new line of mice with a special accessory: an upgraded memory and learning system. When these new 
and improved mice ran through an IQ test, they outperformed normal mice. 
Tsien pulled off an extraordinary engineering trick, creating a lineage of smarter mice. This is 
cowboy science, showing the power of genetic tampering to open the door to evolutionary changes. In a 
world of competition, one would imagine that selection should favor these smart mice who have better 
recall of essential foraging routes, previous social interactions, and places to rest out of harm's way from 
predators. But in biology, there are always trade-offs. Benefits in one area of life are often accompanied 
by costs in others. 
Several months after Tsien's report, a follow-up study of the same memory-enhanced mice 
appeared in print, also in a distinguished scientific journal. But this time there was no media fanfare. The 
new work was carried out by Min Zhuo at Washington University, an ex-member of Tsien's lab and a co-
author of the original paper. Zhuo's new paper confirmed that memory-enhanced mice were indeed 
smarter, but also showed that they were more sensitive to pain, licking their wounds more and for longer 
periods of time than normal mice. Though it is unclear whether Zhuo's results reveal heightened pain 
sensitivity, stronger memories for pain, or some combination of these and other processes, what is clear is 
that the engineering that led to smarter mice led to much more. 
Tsien and Zhuo's work shows that even with targeted, artificial changes in the underlying 
biology, unanticipated consequences are common. It also shows that deep within the biology of every 
organism lies hidden capacities and potential for change. Unleashing these sub rosa capacities can have 
both beneficial and costly consequences for the individual and group. 
The idea I develop in this chapter is that our capacity for evil evolved as an incidental, but natural 
consequence of our uniquely engineered brain. Unlike any other species, our brain promiscuously 
combines and recombines thoughts and emotions to create a virtually limitless range of solutions to an 
ever-changing environment. This new form of intelligence enabled us to solve many problems, but two 
are of particular interest given their adaptive consequences: killing competitors and punishing cheaters in 
a diversity of contexts. But like the painful fall-out from artificially engineering a smarter mouse, so too 
was there fall-out from the natural engineering of a smarter human: a species that experiences pleasure 
from harming others. This is part of the recipe for evil. 
This chapter sets out the evidence to support the idea that evil evolved as an incidental 
consequence of our brain's design. I begin by discussing the two general processes that landed us in the 
unforeseen and uninhabited niche of evildoers: the evolution of byproducts and promiscuous connections 
within the human brain. Because these are general processes, we will take a short reprieve from matters 
specifically evil. 
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What's it for? 
About 50 million years ago, a family of insects—the Phylliinae— evolved a distinctive piece of 
anatomy: a body that looks like a leaf. They also evolved the capacity for catalepsy or statuesque 
stillness. Their leafy body is so exquisitely designed that even predators with superb search images are 
fooled as they walk or fly by. But from the fact that the leafy body provides these insects with an 
invisibility cloak, and the fact that this enables them to escape predation, we cannot conclude that the 
leafy body evolved for predator evasion. What something is used for today may be different from what it 
evolved for— the difference between current utility and original function. To show that the leafy body 
evolved for predator evasion, we need to know more, which we do. For one, the leafy body is paired up 
with a requisite behavioral adaptation: turning to stone. If leaf insects fluttered about as actively as any 
other insect, their motion alone would cry out to the predators. Optimal effectiveness requires acting like 
a leaf. But acting like a leaf without the leafy body has its own independent benefits, paying off in terms 
of predator evasion, as well as sneaking up on potential mates. It would therefore make good sense if 
stillness evolved first followed by a leafy body. This is precisely what evolution's record reveals. 
The adaptive advantage that comes from statuesque stillness and a leafy camouflage can only be 
measured against the backdrop of today's predator line-up. If some future-predator evolves more 
sophisticated abilities to discriminate real leaves from faux leaves, the Phylliinae will be out of luck. This 
new pressure from predators will, in turn, push for new evasive tricks, thus initiating the classic cycle of 
predator-prey evolution. What is adaptive for the Phylliinae today, may not be adaptive tomorrow. 
The comparative study of the Phylliinae raises a class of questions posed by all evolutionary 
biologists, independently of their taxonomic biases or interests in physiology, morphology, or behavior: 
How did it originally evolve? What adaptive problem did it solve? Did it evolve to solve one adaptive 
problem, but over time shift to solve another— a case of what the late evolutionary biologist Stephen J. 
Gould referred to as an exaptation? Does the exaptation generate profits or losses for survival and 
reproduction? Is the trait associated with byproducts, incidental consequences of the evolutionary 
process? What effects, if any, do these byproducts have on survival and reproduction? These questions 
apply with equal force to evil as they do to language, music, mathematics, and religion. The fact that evil, 
relative to a leafy body, is more difficult to define, harder to measure, and impossible to experiment upon 
—at least ethically — doesn't mean we should take it off the table of scientific inquiry. What it means is 
that we must be clear about what we can understand, and how we can distinguish between the various 
interpretations on offer. When we explore the evolution of evil, what are we measuring and what evidence 
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enables us to distinguish between adaptive and non-adaptive explanations? To answer this question, let us 
look at two illustrative examples that are more challenging than leafy coverage in insects: the evolution of 
tameness and religion. 
Sheep, goats, cows, cats, and dogs are all domesticated animals, created by the forces of artificial 
selection. All have been transformed from a wild type to an animal that not only lives with us, but 
sometimes lives for us as food. All are more relaxed, less fearful, and less stressed in the presence of 
humans than their wild ancestors. Many of these animals seek human companionship. These are the 
trademark features of tameness. They are also consistently associated with other features that never 
entered into the breeder's calculations: floppier ears, curlier tails, more mottled fur, greater sensitivity to 
human communication, reduced response to predators, earlier sexual maturation, smaller brains, and 
higher levels of serotonin — a chemical messenger of the brain that regulates self-control. Some of these 
features appear directly relevant to tameness, whereas others appear entirely irrelevant. For example, 
serotonin is critically linked to self-control which is critically linked to an animal's ability to suppress 
aggression when threatened, which is critically linked to building a life with humans. Mottled fur is not 
critically linked to any of these benefits. 
Domestication leads to a pastiche of characteristics, some indicative of the domesticator's goals 
and others orthogonal to it. How does the process of domestication, and artificial selection in particular, 
generate both desired and unanticipated traits? 
In most cases of animal domestication, we know little about how the wild type changed because 
the only available information is either anecdotal or based on loose archaeological reconstructions. 
Consider the domestication of dogs from wolves, and especially the variability among dog breeds. 
Though it is clear that humans throughout history have bred dogs to serve particular functions, including 
herding, aggressive defense, and companionship, each of these personality styles is linked to other 
behavioral and physiological traits. For example, breeds with high activity levels are smaller than breeds 
with low activity levels, aggressive breeds have higher metabolic rates than docile breeds, and obedient 
breeds live longer than disobedient breeds. Does selection for aggressiveness cause an increase in 
metabolic rate or does selection for higher metabolic rate allow for heightened aggressiveness. Because 
these are all correlations, we don't know which trait pushed the other to change or whether both traits 
were favored at the same time. 
There are two situations that provide a more clear-cut understanding of which feature was favored 
by selection and which emerged as an incidental byproduct: controlled experiments and domestication 
efforts that resulted in unambiguously undesirable traits. In the 1950s, the Russian biologist Dmitry 
Belyaev set out to domesticate the wild silver fox. Over several generations, he selectively bred those 
individuals who were most likely to allow a human experimenter to approach and hand them food. After 
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45 years of selective breeding he got what he aimed for: a population of tame foxes, less fearful of 
humans and more interested in playing with them. But Belyaev also got much more than he aimed for: 
these tame foxes had floppier ears, curlier tails, smaller brains, higher serotonin levels, and much sharper 
social skills than their wild relatives. These tame foxes acquired the same package that virtually all other 
domesticated mammals had acquired: some desired and desirable traits and some surprises. 
Belyaev's study shows that even under highly controlled laboratory conditions, artificial selection 
leaves a trail of unanticipated consequences, traits that come along for the ride. This link between desired 
and unanticipated features arises because the genes that create these features are like coupled oscillators: 
changes in the expression of one gene directly link to changes in the expression of others. At the level of 
the traits—the gene's expressions—some have no impact on survival or reproduction, while others may 
increase or decrease these aspects of fitness. We can illustrate this point by looking at an example from 
dog breeders. 
Several hundred years ago, dog breeders used artificial selection to create snub-nosed breeds such 
as the pug, bull dog, and boxer. The idea was to satisfy our aesthetics for diminutive noses, and reduce 
the size of the dog's classically large protuberance. Over the course of several generations of picking the 
smallest-nosed members of the litter, pugs, bull dogs, and boxers emerged. But they also emerged with 
an unanticipated and maladaptive health problem: all of these breeds have a harder time breathing and 
staying cool than full-nosed or snouty dogs. No breeder would select for respiratory problems or an 
inability to stay cool. These traits emerged as costly byproducts of selection for a diminutive nose, and 
more abstractly, as a byproduct of our aesthetics. As in Tsien's experiments on memory enhanced mice, 
when we tamper with nature, we can cause great harm. 
Research on the evolution of religion provides my second example of how to think about 
adaptations and byproducts. The different types of religion are like the different dog breeds: distinctive in 
many ways, but with a large number of shared traits in common. Most religions have a set of rules for 
group membership and expulsion, ritual practices, and beliefs in the supernatural. These commonalities 
suggest to some scholars that religion evolved to solve a particular problem, one that all humans confront. 
That problem is large scale cooperation among unrelated strangers, a topic I pick up in greater detail 
further on in this chapter. Other species cooperate, usually with a small number of individuals, mostly 
close kin. As the size of potential cooperators grows, and genetic relatedness among individuals within 
the group shrinks — adding more unfamiliar strangers to the mix — the potential risks of cooperating 
with a cheater increases. Religion, and its core features, evolved to diminish this risk and increase the 
odds of developing a society of stable cooperators. Viewed from this perspective, religion is an adaptation 
— in the evolved for sense. 
For those scholars who favor the idea of religion as adaptation, supporting evidence comes from 
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analyses of historical data together with experiments. Religious groups show higher levels of 
cooperation, often over longer periods of time, than many other organized, but non-religious groups. 
Religious groups also tend to last longer as groups than non-religious organizations or institutions. 
Cooperation among religious groups is often facilitated by punishment or the implication of punishment 
from a deity. In a study of 186 societies by the biologist Dominic Johnson, analyses showed that those 
who believed in a strong moralizing god, capable of doling out punishment, engaged in higher levels of 
cooperation, including paying taxes, complying with norms, and repaying loans. These observations are 
complimented by experiments showing that people are more generous about giving away their money in a 
bargaining game, and less likely to cheat, when they think about words associated with religion — divine, 
God, spirit, sacred, prophet — than when they think about neutral words. For example, in the dictator 
game, involving two anonymous players, one decides how much of a pot of money to give to the other. 
The recipient has no say, and is thus stuck with whatever the donor offers. In general, donors give either 
nothing or about half. When primed to think about religion, donors are more likely to give than keep the 
entire pot, and give more as well. 
The implication of these results is that the religiously-minded feel that they are being watched. 
Cueing up words that are indicative of their religious beliefs, heightens their vigilance and their moral 
obligations. Religion fuels altruism and fends off the temptation to cheat. 
All of the observations and experiments discussed above are fascinating and relevant to 
understanding the role of religion in past and present societies. But this evidence is irrelevant for 
understanding the evolutionary origins of religion. It is irrelevant because it can't determine whether 
religion originally evolved to solve the problem of large scale cooperation among strangers or whether it 
evolved for other reasons but was then used in the context of cooperation. This alternative explanation 
sees religion as an exaptation. No one doubts that religion provides social cohesion. No one doubts that 
religion also sends a buzzing reminder to the brain's moral conscience center. But from a description of 
what it does today, or even in the distant past, we can't conclude that it evolved for this purpose. That 
religious organizations show higher levels of cooperation than non-religious groups doesn't mean they 
evolved for cooperation. We also can't conclude that religion's effectiveness as social glue relies on 
uniquely religious psychological thoughts and emotions. Though the creation of and belief in 
supernatural powers may be unique to religion, other foundational beliefs and emotions are shared across 
different domains of knowledge: young children attribute intentions, beliefs and desires to unseen causes, 
including the movement of clouds and leaves; non-religious moral systems use punishment to embarrass, 
recruit regret, and fuel shame; like many religions, non-religious institutions also attempt to reprogram the 
thoughts and beliefs of its members—think of all the global rebel operatives that brainwash innocent 
children into becoming child soldiers. Religion helps itself to non-religious psychology. The utility of 
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religion looks like a case of exaptation — an expression of human thoughts and emotions that originally 
evolved to solve problems other than cooperation, but once in place were swiftly adopted for solving 
problems of cooperation. 
Further evidence in support of religion as exaptation comes from a follow-up to the dictator game 
experiment discussed above. If you swap religious words for non-religious but moral words such as civic, 
duty, jury, court and police, you get the same results: people give more money when thinking about these 
morally-pregnant, but non-religious words. It is also the case that if you paste up a photograph of eyes 
next to a money box for coffee, people give more than with a photograph of flowers. What these two 
studies show is that words and images that make us think about others, especially the possibility that 
others are watching, turns us into bigger spenders. These psychological transformations are not, however, 
specific to religion. Some may think that God is watching, but they and others may also think of a white-
bearded, gavel-wielding, atheistic judge. 
We learn three important lessons from the study of tameness and religion, lessons that will propel 
our discussion of evil. First, distinguish what something evolved for from what it is used for. Second, 
dissect complicated traits down into their component pans as the parts, together with their inter-
dependence, may have different evolutionary histories. Third, the combination of independently evolved 
capacities can lead to novel adaptations and possibilities. Some combinations lead to altruistic and 
humane compassion toward those we don't know. Others lead to virulent hatred and annihilation of those 
we do know. The brain's promiscuity is a driving engine for both the good, the bad, and the ugly. 
From the shackles of monogamy to the freedom of promiscuity 
Many years ago, some American friends of mine were married in a small village in Tanzania. After the 
wedding, they went to a local official who was responsible for providing a marriage certificate. On the 
certificate were three choices, indicative of the type of marriage: Monogamous, Polygynous, and 
Potentially Polygynous. My friends chuckled, but aimed their pen with confidence at Monogamous. 
Before they could ink the certificate, however, several Tanzanian men shouted out "NO! At least 
Potentially Polygynous. Give yourself the option." Right, the option. The freedom to explore. 
Among social animals, only a few species pair bond for life, or at least a very long time. This fact 
is equally true of the social mammals: less than 5% of the 4000 or so species are strictly monogamous. 
For these rare species, most of their efforts to think, plan, and feel are dedicated to their partner; what's 
left over goes into finding food and avoiding becoming dinner. Life is much more complicated for the rest 
of the social animals. Their social and sexual relationships are more promiscuous, less stable and less 
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predictable. This unpredictability is partially responsible for changes in the brain. Promiscuous mating 
systems demand more flexibility, creativity and out of the box thinking. 
The anthropologist Steve Gaulin explored the idea that a species' mating system is directly 
related to its capacity to think. Gaulin started by looking at two closely related species of voles, one 
monogamous and the other polygynous. In the polygynous vole, males typically mate with multiple 
females. To achieve this kind of mating success, males have large territories that encompass many 
smaller female territories. In the monogamous species, the male and female share the same territory, with 
mating restricted to the couple. These differences in mating system and space usage have two direct 
consequences: relative to the monogamous male vole, the polygynous male vole must travel much further 
in a day than the females and must recall where the female territories are located. For a polygynous male 
vole, mating success depends on long day trips, visiting each of the female territories. For the 
monogamous male vole, there are no physical or memory challenges as the female is virtually always 
nearby. Given the costs to a polygynous male vole of forgetting where the females live, there should be 
strong selection on the memory system. Gaulin confirmed this prediction by showing that polygynous 
male voles outcompete females of their species in a maze running competition, and also have larger 
memory systems than females. In the monogamous vole, there are no sex differences in maze running or 
memory. 
Gaulin's work provides a gorgeous example of how evolutionary pressures can act on the brain to 
create differences in psychological capacity. Other examples abound, including evidence that fruit eaters 
have larger brains than leaf eaters, primates living in large social groups have larger frontal lobes than 
those living in smaller groups, and bats living in open habitats have smaller brains than those living in 
complex closed habitats. In each case, a particular ecological or social pressure — finding ripe fruit, 
updating the status of numerous social relationships, avoiding obstacles while in flight — sculpts 
differences in brain anatomy and function. Some of these pressures favor extreme specialization and 
myopia, whereas others favor a broader vision. Relative to every healthy member of our species, all other 
animals have tunnel vision. When our ancestors began to migrate out of Africa, the diversity of 
environments and social opportunities favored generalists with a broad and flexible vision. 
To appreciate the significance of the human revolution in brain engineering, consider three cases 
of myopic, but highly adaptive intelligence in other animals, cases that lack the signature of intellectual 
promiscuity; these cases are of particular interest because they represent the kinds of examples that 
caused Darwin to doubt the beneficence of God, to reflect upon the cruelty of nature, and to ponder the 
problem of evil: 
• The wasp Ampules compressa tackles a specific species of cockroach, inserts a 
first stinger into its body to cause leg paralysis and eliminate fighting, then a second 
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stinger into the brain that causes intense auto-grooming followed by three weeks of 
lethargy. During this down time, the cockroach turns into a living meal for the wasp's 
larvae. 
Brazilian parasitoid wasp of the family Braconidae, lays its eggs inside a 
particular species of caterpillar, and once the larvae are fully developed, they hatch out of 
the caterpillar. Though it is strange enough for caterpillars to function like incubators, 
these innocent larvae were anything but innocent while developing inside the caterpillar. 
Once the larvae hatch, they are treated to an unprecedented level of care from the 
caterpillar who, Gandhi-like, foregoes all eating and moving to protect its adopted young, 
including violent head-swings against any intruder. The wasp has effectively brain-
washed the caterpillar, hijacking its evolved instincts to care for its own young. 
•A solitary wasp in the genus Seeliphron selectively feeds on the dangerous and 
much larger black widow spider, using two tricks: it secretes a substance that is like 
Teflon, allowing it to move into a spider's web without getting stuck; next, it flails 
around in the web to attract the spider, and once the spider is positioned above in kill 
mode, the wasp launches its stinger, piercing the spider right through the brain. End of 
black widow. If the wasp makes the slightest mistake, end of wasp. 
The capacity that has evolved in these wasps is myopically focused on one problem, and one problem 
alone. Despite the mind control and deception that is part of their evolved competence, they don't deploy 
these skills in any other context. This highly adaptive and monogamous pattern of thinking runs 
throughout the animal kingdom and across different contexts, including male cleaner fish that attack 
female cleaner fish who violate the rules of mucus-eating from their clients, but do not deploy such 
draconian measures in other situations; birds that feign injury to deter predators from their nest, but 
deceive in no other context; cheetah mothers who demonstrate to their cubs how to bring down prey, but 
never provide pedagogical instructions in other relevant domains of development; and monkeys that 
understand how to use tools generously provided by humans but never create any of their own. 
Like other animals, we too are equipped with adaptive capacities that evolved to solve particular 
problems. Unlike other animals, however, these same adaptive specializations are readily deployed to 
solve novel problems, often by combining capacities. Like wasps, we deceive, manipulate and parasitize 
others, often cruelly. But unlike wasps, we don't use these abilities with one type of victim in one context. 
As long as the opportunity for personal gain is high relative to the potential cost, we are more than willing 
to deceive, manipulate, and parasitize lovers, competitors and family members. When we attack rule 
violators, not only do we do so in the context of cheaters who eat but don't pay, but also deadbeat dads 
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who fail to care for their young, cads who have extramarital affairs, and trigger-happy murderers who 
take the lives of innocent people. What changes in the brain enabled us, but no other species, to engage in 
promiscuous thinking? 
To understand what changed in the brain, it is useful to paint a few broad-stroke comparisons, and 
then narrow in on the details. We know, for example, that brain size changed dramatically over the 
course of our evolutionary history, ultimately reaching three times the size of a chimpanzee's brain with 
the appearance of the first modern humans some 100-200,000 years ago. From the archaeological 
evidence, we can infer that some aspect of the internal workings of the brain —not simply size —must 
have changed at about the same time in order to explain the appearance of a new material culture of tools 
with multiple parts and functions, musical instruments, symbolically decorated burial grounds, and cave 
paintings. Before this period, the material culture of our ancestors was rather uncreative, with simple tools 
and no symbolism. The new material culture was heralded by a mind unlike any other animal. No other 
animal spontaneously creates symbols, though chimpanzees and bonobos can be trained to acquire those 
we invent and attempt to pass on. No other animal creates musical instruments or even uses their own 
voice for pure pleasure. No other animal buries its dead, no less memorializes them with decorations; ants 
drag dead members out of their colony area and deposit them in a heap, though this is driven by hygiene 
as opposed to ceremonial remembrance and respect. Only a species with the capacity to combine and 
recombine different evolved specializations of the brain could create these archaeological remains. This 
period in our evolutionary history marks the birth of our promiscuous brain. The brain sciences have 
helped us see the fine details of this new species of mind. 
The comparative anatomists Ralph Holloway, James Rilling, and Kristina Aldridge have 
analyzed brain scans and skull casts of humans and all of the apes: chimpanzees, bonobos, gorillas, 
orangutans, and gibbons. This sample represents approximately 15 million years of evolution, and 
includes considerable diversity in mating systems, dietary preferences, use of tools, group size, life span, 
locomotion style, communication system, aggressiveness, and capacity for cooperation. Thus, gibbons are 
monogamously pair bonded, live in small family groups in the upper canopies, swinging and singing to 
defend their territories, never use or create tools, are omnivorous, restrict cooperation to within the 
family group, and show little aggression. Gorillas are folivores or leaf eaters, live in harem societies, 
knuckle walk on the ground, rarely use or make tools in the wild, show aggression primarily between 
harems, communicate with a diversity of sounds, and show limited cooperation even under captive 
conditions. Chimpanzees are promiscuous, omnivores who hunt for meat on the ground and in the tree 
tops, create a diversity of tools that are culturally distinctive between regions, communicate with a 
diversity of sounds, are lethal killers when they confront individuals from a neighboring community, and 
are cooperative especially in competitive situations. Despite this diversity, nonhuman ape brains are much 
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more similar to each other than any one is to a human brain. What changed since we split off from our ape 
cousins is both the overall geometry of the brain in terms of the relative size of different components, as 
well as the connections both within and between these components. Some of the most spectacular 
changes evolved within the frontal and temporal lobes, as well as their connections to other areas of the 
brain involved in the control of emotion and stress. These circuits play a critical role in decision making, 
self control, short-term memory, social relationships, tool use and language. 
For detail, and further evidence of the importance of connectivity in promiscuous thinking, we 
turn to brain imaging studies of healthy adults, developing children, and patient populations that lack the 
signature of promiscuity. Consider tool use. Though a wide variety of nonhuman animals use tools, only 
humans create tools that combine different materials, have multiple functioning parts, can be used for 
functions other than the one originally designed, and function in the context of survival, reproduction, and 
leisure. These properties are the signature of a promiscuous brain. When we look at the material culture of 
the most sophisticated animal tool user — the chimpanzee — we see tools that use a single material, have 
only a single functional part, are only designed for one function, and the function set is strictly limited to 
survival or reproduction. Something as simple as a pencil, beyond the chimpanzees' wildest imagination, 
consists of multiple materials (rubber, wood, lead, metal), was designed for writing but can be used for 
poking or keeping hair up in a bun, and has two functional parts (lead for writing, rubber for erasing). 
When you put a human subject in a brain scanner and record activity during observations of tool use, 
what you see is an orchestrated coordination between different and connected brain regions. There is 
activity in regions carrying out spatial analyses, motor behavior, goal directed assessments, and object 
recognition, and much of this activity is fed forward to the frontal areas for storage in working memory as 
well as judgment and evaluation. A healthy adult brain is a heavily connected brain. Promiscuity results 
from a network of interconnected brain regions. 
Even resting brains show signs of promiscuity. When you lie down in bed and close your eyes, 
but before you drift off to sleep, your brain— assuming you are an adult and healthy — shows activity in 
a family of inter-connected brain regions called the default network. This is your brain at rest, but it is 
anything but at rest. Some of the most active areas involve those that are engaged when we evaluate 
social relationships, consider what others believe and desire, who they are, and how we might interact in 
the future. This same default network looks very different in children, as well as in the elderly: it is much 
less connected. Growing up is connecting up. Growing old is disconnecting. We gain promiscuous 
thinking as we mature and lose it as we age. 
If connection is key, then disorders of the mind or physical insult should result in predictable loss 
of promiscuity. A brain imaging study of individuals with autism is revealing. Individuals with autism 
fall along a spectrum, from low to high functioning. Though this spectrum captures important 
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differences, all inflicted with this developmental disorder have difficulty understanding the beliefs, 
intentions and emotions of others, and often become hyper-aroused when seeing, hearing, or touching 
rather unremarkable objects or events. All of these capacities require a system that can integrate multiple 
sources of information. During brain scanning, individuals with autism show a striking reduction in 
activity in an area called the insula and its connection to both the somatosensory cortex and amygdala. 
The insula is an area of the brain that is like a traffic cop, responsible for coordinating the flow of 
information in the brain, both where it is coming from and where it should go. The somatosensory cortex 
handles our body's response to the world, including its state of arousal. The amygdala plays a key role in 
emotional processing, and more generally, in generating positive or negative assessments about the value 
of an experience. With the traffic cop asleep, and the body's arousal and emotional hubs dormant, it is no 
wonder that those with autism lack empathy, can't understand what it means for someone to be in love, 
are befuddled by deception, and find the bombardment from our media-intense world truly 
overwhelming. The lack of connectivity among those with autism is proof that connectivity is necessary 
for promiscuous thinking. 
Once we evolved our massively connected, promiscuous brain, tool use, communication, 
mathematics, music, and morality were transformed. No longer were we constrained to think within the 
confines of the evolved context. We could take aspects of an ancient psychology that evolved for one 
problem and use it for new purposes, some beneficial to us individually and as members of a group, and 
some costly to our own and others' survival. 
Consider our capacity to defend members within a group against attack from individuals outside 
the group. Many, perhaps even the majority of religious groups have carried out this mission, some with 
violence such as the Catholic-Protestant conflict in Ireland, and some with tranquility such as the 
Tibetan's plea for peace amidst a powerful Chinese oppressor. The process starts, however, with an 
ancient system that we share with all socially living animals. To survive and reproduce, individuals 
cooperate with members of their own group and defend their resources against members of neighboring 
groups. All animals, humans included, recognize group members by distinctive markings or recalling 
features associated with specific individuals. We transformed this evolutionarily ancient capacity into a 
distinctively human one by combining it with our systems of language, morality, and beliefs. This 
combination allows us to use symbols to demarcate those within our group from those outside, to tie these 
symbols to distinctive beliefs, values, and emotions, and to use these different psychological systems to 
caricature the other as buffoon, vermin, parasite, or inanimate cargo. This combinatorial process allows 
us to cleanse the in-group by annihilating the out-group. It allows us to increase cooperation within a 
group while ramping up the defenses to take out enemies living outside the group. This strategy is 
simple and effective. First, convince one group of people that another group has a set of undesirable traits, 
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features that will undermine the success of the in-group. This has the effect of tightening the bonds 
within the group. Next, convince the in-group that those undesirable qualities make the others less-than-
human and barely nonhuman. Next, make sure that the nonhuman mascot for the out-group is vile, 
abhorrent, and disgusting. This ingredient is critical as it guarantees that each member of the in-group will 
feel a surge of disgust every time it sees or hears of the out-group. Once disgust is in motion, there is 
only one additional step: either destroy or purge the other of its vile qualities. Destruction is not only 
permissible, but morally obligatory, carried out guilt-free because the mind has taken the other out of the 
moral domain and into the domain of property — either dispensable, controllable or transformable. 
Taking out the other is rewarding. Harm feels good. 
Our uniquely promiscuous minds invented dehumanization, using a recipe of adaptive ingredients 
— defense against an enemy, disgust as a response to noxious and unhealthy substances, and creative 
language use. This is a dangerous idea, one I develop in chapter 3. It is one of many capacities that 
enabled us to uniquely imagine new ways of inflicting excessive harm on others. It is a capacity that, 
nonetheless, has a deep evolutionary history. 
HARMING OTHERS, version 1.0: non-lethal behavioral routines 
All animals are motivated to secure resources that will enable them to survive and reproduce. At the most 
basic and universal level, this is what life is all about. Gaining access to resources enables individuals to 
accrue more resources, live longer, and produce more offspring. The path to acquiring resources is 
complicated by two facts of life that were central to Darwin's insights into the process of evolution: 
resources are limited and individuals must compete with others from the same and different species for 
these resources. Competition is the breeding ground for aggression — the most basic means of harming 
others. Aggression is a natural outcome of living in a social world where supper, sex, and space never 
come prepared on a silver platter. Here I explore the core properties of non-lethal aggression, a manner of 
harming others that is part of every animals' behavioral repertoire. This discussion sets the stage for 
understanding how evolution's R&D operation enabled a transformation of the non-lethal form of 
aggression into a lethal form, and ultimately, into an excessively lethal form that is the trademark of 
human evil. It also shows how the social norms guiding animal aggression evolved into moral norms, and 
thus, why we perceive some forms of aggression as deeply wrong, unethical and grotesque. 
Consider life on Earth before human existence, say 10 million years ago. Our closest living 
relatives the chimpanzees and bonobos are living in the forests of Africa, and so too are dozens of other 
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primates, mammals, birds, reptiles, amphibians, fish, and insects. And of course, there are animals 
populating every other continent and the seas that surround them. Among the social animals—those 
living in groups—the common form of aggression is one-on-one, and the context is typically 
competition over food, a place to rest, or access to a mate. Sometimes the aggression is initiated as an 
attack and sometimes it is in self-defense. Sometimes it is highly ritualized and planned, and sometimes it 
is a reactive free-for-all. Sometimes it occurs within the group and sometimes between. Severe injuries 
arise, but deaths are rare. The aim is to resolve a competitive dispute by means of non-lethal aggression, 
and if possible, non-physical contact. If someone dies it is because an injury leaves them incapacitated or 
vulnerable to disease. It is not because their opponent aimed to kill. The ubiquity of non-lethal aggression 
points to a suite of common biological ingredients, a core set of neurobiological, hormonal and 
psychological adaptations that constrain how animals fight. 
It all starts with one individual perceiving a valuable resource that is within reaching distance of a 
competitor. What launches a first move and subsequently guides the process to its completion with a 
winner and a loser? In some species there are rules of thumb that deflate any aggressive instincts before 
they are launched, even though there are clear competitive interests. For example, in territorial lizards 
and birds, if an emigrating individual lands in an area and sees or hears another individual vigorously 
displaying— push-ups with colorfully flashing neck sacs in lizards, vocal arias in birds —they move on. 
The rule: territory owners win, no questions asked. Another rule of thumb arises in species organized 
around either permanent or breeding-only harems: one male and many females. Two classic cases are the 
well-studied hamadryas baboons of Ethiopia and the elephant seals of California. In both species, males 
are much larger than females, with elephant seals providing an extreme case— the harem master can be 
ten times bigger than the females he mates with. In hamadryas, no one challenges the male over access to 
the females in his harem. Competition arises in acquiring females into a harem, a process that starts early, 
with individual males recruiting juvenile females. In elephant seals, either one or a few males completely 
monopolize the mating among the often hundred or more females within the harem. These males rule. As 
evidenced by genetic fingerprinting, virtually all of the offspring are sired by 1-3 males. No mating 
competition. Competition arises when the young turks try to wear down the harem master through 
repeated challenges over the season. Eventually, often over the course of several mating seasons, the 
harem master loses a fight and hangs up his gloves. 
Dominance hierarchies provide another set of rules or norms that guide competition, and thus 
aggression. In general, irrespective of the species, high ranking animals outcompete low ranking animals 
for access to resources. If the spread between two individuals within the hierarchy is large, the 
subordinate acts like a migrating lizard or bird landing in a resident's territory: no contest, no competition, 
no fighting. If the spread is less, say two individuals who hold adjacent positions within the hierarchy, 
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then other factors enter into the calculation. This is where things get interesting as these other factors 
determine the start and end of a contest. 
Insights into the dynamics of aggressive competition emerged in the late 1970s and early 1980s 
due to two fundamental developments within evolutionary biology. The first involved a marriage 
between economic game theory and evolutionary biology. This marriage was set up by the British 
evolutionary biologist John Maynard Smith who recognized that for any competitive interaction, there are 
different strategies, each with different payoffs. Some strategies are more costly, but return greater 
benefits. Others are more conservative and less costly, but return smaller benefits. How well any given 
strategy does depends on its frequency in the population, and thus, on whether the particular strategy is 
dominant or rare. For example, consider a baboon troop with 20 adult males. Imagine that one of the 
males decides to bare his canines, stand up on his two hind legs, and charge whenever anyone comes near 
him and he is eating. This male is displaying his intent to attack at the slightest provocation. One could 
imagine that this would be very effective, especially if he is the only one displaying in this way. But if 
this display pattern spreads, and all 19 other males do the same thing, then this strategy fails as it no 
longer distinguishes among the 20 males in the troop. What evolutionary game theory tells us is that the 
effectiveness of a strategy depends on how common it is within the population. Power comes, in part, 
from being not too common or predictable. 
The second development involved signaling theory, and a challenge to the traditional approach 
that considered animal signals as truthful messengers of information. On the traditional view, when a 
monkey bares his canines, he is signaling his motivation to attack. When a dog puts his tail between his 
legs, he is signaling his submissive status. When a bird gives an alarm call, she is telling others that a 
predator is nearby. When a human smiles, he is conveying his desire for friendship. The new signaling 
theory presented a challenge to this honest view of communication. Why, for example, wouldn't 
individuals lie, deceiving others into believing that they were really tough, meek, in danger, or friendly, 
only to take advantage of the situation and gain added resources. Why, for example, wouldn't a baboon 
who was actually afraid, put on a tough-guy show and scare off his opponents? Why wouldn't a dog who 
was actually tough, send a submissive signal at the start of the interaction, cause his opponent to lower his 
guard, and then attack? Why wouldn't a bird send an alarm in the absence of danger, knowing that others 
will run for cover and leave all the food behind—no competition? Why wouldn't a human who actually 
wanted to lure in an innocent victim for robbery send a seductive smile? This line of questioning, 
developed by the British evolutionary biologists Richard Dawkins and John Krebs, led to a number of 
studies showing that animals are engaged in a much more complicated and dynamic dance when they 
compete. Static properties of the animal — its height, weight, tail length, antler size — indicate its raw, 
unfakeable ability to fight or what biologists call Resource Holding Potential or RHP. A deer with a large 
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set of antlers has paid the costs of growth, and is thus, a serious opponent with considerable strength. A 
tall, heavy, long-tusked elephant bull has spent the time and energy to bulk up, and can throw this weight 
around in a fight. Added on to an animal's RHP are dynamic properties, features that require energetic 
investment in the moment such as the loudness or duration of a vocalization, or the height of a jump 
display. These dynamic properties form the foundation of competitive interactions, and the raw material 
for assessments. When a resource is up for grabs, and no simple rule of thumb or RHP factor trumps, 
animals assess each others' displays, working out whether to flee or escalate. What, if anything in a 
display, reflects the signaler's true capacity and motivation? 
The Israeli evolutionary biologist Amotz Zahavi provided a simple, yet far-reaching explanation 
of honest signaling. Honesty, in the animal world, is simply about prediction. When a kob standing on his 
territorial mound charges toward another, to what extent does this display predict that he will continue the 
attack if the opponent doesn't flee? Is he all smoke or does the display accurately predict the follow-
through? When a mantis shrimp uses his powerful claw to thump the sand at an intruder, will he go 
further, thumping the intruder who continues to advance? Zahavi's solution was based in economics: 
signals are honest if and only if they are costly to produce, where cost is relative to current condition or 
health. If every kob can charge even if they are blowing smoke, the charge display carries no weight. It is 
pure puffery and dishonest. If every mantis shrimp can thump with its appendage, and does so regardless 
of its current power, then sand thumping loses value. For a charging display or sand thumping to carry 
value, they have to be costly to produce and only those in good enough condition should be able to 
tolerate the costs. Numerous studies support Zahavi's insight, including work on insects, crabs, birds, and 
gazelles, as well as hunter-gatherers and religious institutions. Hunter-gatherers do it by showing off and 
sharing their large prey capture, whereas religions do it by showing their commitment to long and 
involved ritual displays. 
The vast majority of animal competition is settled by means of non-lethal aggression. Animals 
adopt different strategies, use rules of thumb, and engage in assessment in order to minimize the costs of 
battle. This is version 1.0 of HARMING OTHERS. This version operates within every animal, humans 
included. Over time, some animals evolved hormonal and neural upgrades that changed how individuals 
experienced the thrill of victory and the agony of defeat, as well as changes in their willingness to take 
risks. These upgrades inched animals closer to lethal aggression, pushed some right into it, and others 
over the top. 
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HARMING OTHERS, version 1.1: microcontrollers 
In any competitive situation, whether it is animals working out a strategy for maximizing the odds of 
obtaining food or humans working out a strategy for maximizing the odds of check mating an opponent's 
king, someone will walk away as the winner and someone as the loser. Winning feels good and losing 
feels bad. Winning fuels confidence, losing lowers self-esteem. Depending on the opponent, including 
what they look like and whether they are familiar or unfamiliar, it is possible to gauge the likelihood of 
winning or losing in advance. Depending on the individual's prior history of wins and losses, and details 
of his or her personality, some individuals will embrace the challenge of a high risk-high payoff strategy 
whereas others will adopt a low-risk low payoff strategy. Winning, losing, and taking risks are all 
mediated by differences in hormone levels, neurochemicals, and patterns of brain activation. Some of 
these differences are set by the individual's biology, some change over the course of a year, some within a 
day, and some within the period of a brief glance that allows for an opponent to assess the competition. 
These physiological processes are the microcontrollers that regulate an individual's motivation to fight or 
flee, as well as the sense of reward and loss that accompanies winning and losing. These microcontrollers 
adaptively regulate the capacity to harm, at least until they malfunction. Malfunctions, whatever their 
cause, can convert healthy, defensive, competitive, and justifiable harms into over the top excessive and 
unethical harms. 
One of the primary microcontrollers is the hormone testosterone. Though it is commonly assumed 
that testosterone is a male hormone, it is also present in females, though at lower concentrations. 
Testosterone plays an essential role in both sexual and aggressive behavior in all social animals. 
Testosterone surges when males defend their territories, and also, when they recruit sexually available 
females. Stronger surges occur when individuals are challenged by competitors who want their territory, 
food, mates, or position within a hierarchy. What this shows is that testosterone motivates animals within 
the arena of competition. 
Testosterone also surges again after an individual wins a fight, and drops following a loss. This is 
highly adaptive as it motivates winners to keep defending their resources, and motivates losers to give up 
and minimize future costs. Across a wide variety of species, humans included, winners are two times 
more likely to win the next fight whereas losers are five times less likely to win the next fight. These 
winner-loser effects are mediated by testosterone. In our own species, among male and female athletes, 
in sports including soccer, tennis and judo, winners show higher testosterone levels than losers. This 
effect even holds in non-physical competition, such as chess and stock trading. In a study of day traders 
on the London Stock Exchange, those making the highest profits had the highest levels of testosterone. 
Even those who are simply witnesses to a winning competition show increases in testosterone, including 
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cichlid fish spectators observing a winning fight, and soccer spectators seeing their team win the World 
Cup. 
What many volumes of experiments reveal is that testosterone plays a fundamental role in social 
behavior across the animal kingdom, motivating individuals to defend their resources, acquire additional 
resources when possible, develop confidence following victory, and gracefully walk away following 
defeat. Testosterone influences behavior, and behavior influences testosterone. If an individual 
experiences a challenge, this causes an increase in testosterone. The increase in testosterone heightens 
confidence and risk-taking to defend the resources. Heightened confidence and risk-taking are often 
associated with winning fights. Winning fights increases testosterone, bringing us full circle to the 
challenges of social living. 
Testosterone is joined by several other microcontrollers, including at least one additional 
hormone — cortisol— two neurochemicals—serotonin and dopamine —and several brain areas that are 
affected by these hormones and neurochemicals. Our understanding of this assemblage, beautifully 
synthesized by the psychologist Jack van Honk, accounts for both our adaptive and sometimes highly 
maladaptive capacity to harm others. 
Cortisol mediates the stress response in fish, reptiles, birds, and mammals, including all ages of 
human mammals. When fear kicks in due to aggressive challenges from a dominant individual or from 
the appearance of a predator, cortisol rises. When individuals confront uncertainty, cortisol rises. When 
cortisol levels are high, individuals are more sensitive to punishment and more likely to avoid social 
interactions. Flipping the polarity around, when cortisol levels are low, individuals are more aggressive, 
more reward focused, and less sensitive to punishment. Testosterone and cortisol therefore play within 
the bodies of animals like two children sitting on opposite ends of a see-saw. When testosterone is up and 
cortisol is down, individuals are primed to harm others and take risks. When testosterone is down and 
cortisol is up, individuals are risk averse, less likely to harm and more likely to engage in friendly social 
behavior. 
Serotonin, as noted earlier in the discussion of domestication, is primarily involved in self-
control. High serotonin levels are associated with behavioral inhibition, whereas low serotonin levels are 
associated with disinhibition or impulsivity, as well as heightened aggression. Dopamine is linked to the 
experience of reward, both in terms of predicting when it will occur and in motivating behavior that 
maximizes the odds of obtaining the goods. When animals reach their goals or expect to obtain them, 
including food, mating, or winning a fight, the brain delivers a surge of dopamine. In humans, taking a 
drug that increases the amount of dopamine, causes people to believe that they will feel more elated about 
an event in the future. 
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Testosterone modulates these brain chemicals, suppressing serotonin in the service of heightening 
aggression, and ramping up dopamine to add to the already reinforcing properties of testosterone. But 
like dopamine, testosterone is also directly linked to the reward system. Mice will work a response lever 
to deliver testosterone, and humans become addicted to it. If you inject testosterone into a mouse while it 
is moving about, the location associated with the injection becomes tagged as a favorite spot in the 
landscape, a place to revisit. Drug abusers and gamblers, two personality profiles associated with 
heightened experience of reward and poor self-control, have elevated levels of testosterone and dopamine. 
Twirling inside the brains and bodies of all social animals is a physiological ballet that controls 
the capacity to harm others. This choreography links harming others with the experience of reward. In 
some animals, the link between harm and reward was upgraded to a capacity for lethal aggression. 
HARMING OTHERS, version 1.5: upgrade to lethal aggression 
All social animals have evolved the capacity for aggression, using it to fight members of their own 
species for food, land, and sex. For virtually all animals, winning a fight means chasing away or injuring 
a competitor, but not killing them. There are, however, three situations in which animals kill, two are 
broadly distributed across the animal kingdom and one is extremely rare. In virtually every taxonomic 
group of animals — insects, reptiles, amphibians, fish, birds, and mammals— there are predators and 
prey. Predators are not merely aggressive, but designed to kill prey species for the purpose of survival. 
Also common is infanticide, situations in which adults kill infants. Infanticide is often committed by 
males who have recently entered a group with infants sired by other males. By killing these infants, not 
only does the newcomer obliterate the competition's fitness, but he effectively reboots the female's sexual 
receptivity. Both predation and infanticide entail significant asymmetries in size or weaponry between 
attacker and victim, making the kill relatively cost-free. Rare in the animal kingdom are cases where 
attacker and victim are from the same species, both adults, and thus, comparable in size and weaponry. 
This kind of killing—call it adulticide—only occurs in a small number of species, but the attacks are 
sufficiently frequent to count as part of the repertoire: ants, lions, wolves, chimpanzees and humans. The 
rarity of adulticide raises important questions about the evolutionary pressures that favored this upgrade 
to harming others, as well as the mechanisms that evolved to make it possible. 
Battles among ant colonies are notorious for their organized attacks, designed to kill the enemy 
and minimize costs. Watching ant colonies battle it out piques the imagination, recalling the classic face 
oils between British and French brigades, each side lined up in strategic formation, divided into ranks, set 
up to protect the land and royalty. In his book Lye in the Woods, the American writer and nature lover 
Henry David Thoreau, writes that the ant battles were "deadly combat ... without any noise... I never 
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learned which party was victorious, nor the cause of the war: but I felt for the rest of that day as if I had 
had my feelings excited and harrowed by witnessing the struggle, the ferocity and carnage, of a human 
battle before my door." What is distinctive about ant battles and the deaths that ensue is that they are 
coordinated, with success driven by group size. As the biologist Eldridge Adams has demonstrated, 
bigger groups are more likely to win, more likely to kill a higher number of their smaller opponents, and 
less likely to incur any fatalities. Despite the similarities between ant and human battles, two differences 
undermine the usefulness of this analogy for understanding the evolution of lethal aggression in humans: 
ants are only a very distant evolutionary cousin, subject to extremely different pressures of social life, and 
their cooperative efforts are largely among individuals who are virtual genetic clones. When humans go to 
battle, cooperation is largely among unrelated individuals who are complete strangers. Of the small 
sample of species committing adulticide, chimpanzees are our best bet as they are closer evolutionary 
cousins and they join forces with kin and non-kin. 
To get a sense of lethal aggression in chimpanzees, consider the following description by the 
anthropologist David Watts and his colleagues concerning an attack by males of the Ngogo community of 
Uganda (emphasized words are mine): 
[Field Assistant] G. Mbabazi found 12 adult and three adolescent males, 10 of which had participated in 
the boundary patrol 2 days before ... in the eastern part of the Ngogo chimpanzees' territory. They 
started another boundary patrol by quickly and quietly moving south and then east. At 0830 hr, they 
moved east through a field of elephant grass (Pennisetum purpureum), then reentered the forest and went 
toward the spot where BT, LO, and MO 'three adult male chimpanzees] had been displaying I day 
before and the area where Ngogo males had patrolled the day before that. As they reentered the forest, 
the Ngogo chimpanzees met chimpanzees from another community. The neighboring chimpanzees were 
feeding quietly on Pseudospondias microcarpa fruit in the same tree under which BT, LO, and MO had 
displayed. G. Mbabazi could not ascertain the precise number of chimpanzees from the neighboring 
group, but he saw at least two females with infants, one juvenile, and one adult male that immediately 
fled northeast with the Ngogo chimpanzees in pursuit. The Ngogo chimpanzees caught up to the strange 
adult male after chasing him for about 100 m and surrounded him. Adult Ngogo male EL began to 
pummel the intruder, and adults BF, BRU. LO. and MO quickly joined him. The strange male tried to 
escape down a small hill but could not elude these five Ngogo males and others that joined them. The 
Ngogo males, led by EL, continued to beat, bite, and kick him for 20 min, and dragged him farther 
down this hill into a small stream valley about 50 m away from the spot of his initial capture, where he 
died during or shortly after the attack. All of the Ngogo males remained in the area after the stranger 
was killed. Several circled his body and some sniffed it, while others sat nearby. ...Careful inspection 
showed that the victim suffered wounds across his entire body ... including a deep gash to the bone on 
the left humerus and a deep puncture on the left side of the thorax near the heart. The only missing 
body pan was the victim's testes, which were recovered 50 m away, near where he was initially captured 
(2006, p.g., 166). 
Watts' description captures several important features of adulticide in chimpanzees — both at the 
same field site and others throughout Africa— and in other species. The lethal attacks are explicitly 
proactive and planned. This is important because many cases of non-lethal aggression are reactive and 
impulsive, and studies of human and nonhuman aggression reveal different brain mechanisms underlying 
these two forms of violence. When chimpanzees attack, they use stealth to sneak up on the victim, and 
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then relentlessly hunt them down. When they catch the victim, the attack is brutal, focused on body parts 
that are necessary for moving, communicating and reproducing. The attackers commonly have a 
numerical advantage over the victims, a ratio of at least three to one. This power imbalance reduces the 
costs of the attack by making it almost impossible for the victim to retaliate. Proof of this cost-benefit 
analysis comes from the fact that the attacking party rarely incurs injuries, whereas the victims rarely 
escape alive. The benefit of these attacks is that the attacking community gains access to additional 
resources by weakening the competitive strength of their neighbors. In a well documented case from Jane 
Goodall's site in Gombe, Tanzania, one chimpanzee community literally eliminated their competitors in 
the neighboring community, absorbing the remaining individuals and land. Though such attacks are 
certainly not a daily affair, they occur with sufficient frequency and benefits to create a selective 
advantage for the winners. 
The suite of behaviors that accompany coalitionary killing in chimpanzees has led several 
scientists, most notably Wrangham, to argue that this form of lethal aggression in chimpanzees is an 
adaptation, with deep parallels to human warfare. On this view, we inherited the upgrade to version 1.5 
lethal aggression. 
The claim that our capacity for killing, especially in war, is an evolved adaptation, is anathema to 
many, scholars in the humanities and social sciences. The visceral antagonism is triggered by the belief 
that biological explanations imply inevitability, and provide an excuse for the atrocities we create. For 
these scholars, war, and more generally, the high levels of killing observed among human populations, are 
recent, cultural concoctions, born out of human intelligence, the invention of projectile weapons, and high 
population density, to name a few. From this perspective, biology plays no meaningful role in our 
understanding of human violence. From this perspective, killing in chimpanzees looks nothing like killing 
in humans. This attitude echoes the famous 1986 Seville Statement on violence in which a group of 
distinguished scientists, including the ethologist Robert Hinde, the geneticist John Paul Scott, and the 
biological anthropologist Richard Leakey, sidelined biology with the following five statements: 
I. "It is scientifically incorrect to say that we have inherited a tendency to make 
war from our animal ancestors." 
2. "It is scientifically incorrect to say that war or any other violent behaviour is 
genetically programmed into our human nature." 
3. "It is scientifically incorrect to say that in the course of human evolution there 
has been a selection for aggressive behaviour more than for other kinds of 
behaviour." 
4. "It is scientifically incorrect to say that humans have a 'violent brain'." 
5. "It is scientifically incorrect to say that war is caused by 'instinct' or any single 
motivation." 
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