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
offs 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 Life 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
Hauser Chapter 1. Nature’s secrets 38
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 1 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 part 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
Hauser Chapter 1. Nature’s secrets 39
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:
1. "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."
Hauser Chapter 1. Nature’s secrets 40
These claims led to the rather dreamy-eyed utopian conclusion that “Just as 'wars begin in the
minds of men', peace also begins in our minds. The same species who invented war is capable of
inventing peace. The responsibility lies with each of us.” In essence, understanding our biology will not
contribute to understanding violence and war because we invented war as well as peace, woven out of
nurture’s cloth and her infinite tapestry of cultural potential. These kinds of claims about the role of
biology in human behavior are at best incoherent, and at worst plain wrong. They are also dangerous
because they imply a view of human nature that is infinitely plastic, unconstrained by both universal
features of our biology, as well as individual differences that predispose some to extreme violence and
others to extreme altruism.
What makes the Seville Statement, and other claims like it incoherent is a set of false attributions
to biologists about the role of biology. Statements 2-5 are accurate in that it is incorrect to say that war or
violence are genetically programmed, subject to stronger selection than other kinds of behaviour, built
into the brain as a violent brain, and based on instinct with a single, inevitable output. But I don’t know
any biologists who believe statements like these. The biologist Peter Marler famously spoke of singing in
birds as an instinct to learn, while the evolutionary psychologist Steven Pinker described the Chomskyan
insight into language as the language instinct. A bird’s instinct to learn does not mean that there is a oneto-one,
inflexible mapping between genes or brain circuits and a specific type of song. All songbirds have
the potential to acquire their species’ song, and in some birds, such as mockingbirds and parrots, this
capacity extends to acquiring the sounds of other animals and even inanimate sounds. But if there is no
input at all, or if the bird is deafened, the output is deficient in structure, unrecognizable as a speciesspecific
song. The same holds for the language instinct. Instincts are biological biases that constrain the
range of potential variation. Biology differentiates songbirds from birds that don’t learn their songs. This
same biology allows some birds to learn one song and use it for life, and allows other birds to acquire a
variety of different sounds for use in singing. The biology doesn’t determine the specific content of a
song. The content is determined by what the bird hears, constrained by what its bird brain and syrinx will
process and reproduce. To a large extent, language is no different. Our biology allows us, but not any
other species, to acquire language. This same biology sets up constraints, due in part to what our brains
can keep in memory, what our ears can hear, and what our larynx can produce. Like songbirds, the
specific content of what we say, whether with a French or Vietnamese accent, is determined by where we
live and who we listen to.
If there is any intelligible sense of genetically programmed or instinct, whether for violence,
language, sex, or mathematics, it is that our biology provides us with the capacity to acquire these
domains of knowledge and expression. This doesn’t mean that violence, language, sex or mathematics are
inevitable or fixed in their expression. There are thousands of languages, ways of having sex, and forms
Hauser Chapter 1. Nature’s secrets 41
of mathematical expression. There are also thousands of ways of being violent, and equally, ways of
counteracting such violence. But none of this takes away from the importance of biology, especially its
role in constraining the form that these expressions take in different environmental settings. To think
otherwise is just wrong.
The debate about version 1.5 of lethal aggression gains interest if we restrict the conversation to
the similarities and differences between chimpanzee and human killing. Similarities speak to our shared
evolutionary history, including the mechanisms we inherited and the pressures that favored this form of
violence. Differences speak to both changes in our biology and the environments we confronted and
created.
Those who argue that the comparison between human and chimpanzee killing lacks any
analytical value come from two different camps. On the one hand are anthropologists such as Robert
Sussman and Brian Ferguson who suggest that chimpanzee killing is infrequent, has little benefit in terms
of resources or competition, and is restricted to populations that are either artificially provisioned by
humans or crowded in by us. They also suggest that the archaeological evidence for human warfare
doesn’t really begin until about 12,000 years ago. As Ferguson notes “To argue that war is a result of
some sort of innate predisposition to wage it requires that war be practiced throughout our prehistoric
past.” This date, so Ferguson continues, is too recent to invoke natural selection as a cause, and leaves
unexplained why there is no earlier evidence of massive killing if our last common ancestors had this
capacity.
These criticisms either fly in the face of contradictory evidence or have little to do with the
original ideas. Concerning chimpanzee killing, the evidence comes from multiple sites in East and West
Africa, including sites with no provisioning and no crowding from humans. Further, analyses by
Wrangham and his colleagues show that humans living as hunter-gatherers or subsistence farmers on the
continents of Africa and South America, engage in coalitionary killing, using stealthy raids and
imbalances of power to minimize the costs and maximize the benefits. Looking at 32 different small
scale societies, calculations of the median death rate were between 164-595 per 100,000 per year.
Looking at 9 chimpanzee communities spanning 5 populations in Tanzania, Uganda, and Ivory Coast, the
rate was 69-287 per 100,000 per year. Chimpanzees fall well within the range of human hunter-gatherers
and subsistence farmers. This evidence not only shows parallels between chimpanzees and human
societies living under conditions most like our ancestors, but also provides a resounding rejection of the
view that chimpanzee killing is infrequent and of trivial importance. If the rates of killing are comparable,
then either they are trivial for both species or trivial for neither. Given that both chimpanzees and human
hunter-gatherers live in small groups, killing even a few individuals can have a dramatic effect on their
capacity to defend resources.
Hauser Chapter 1. Nature’s secrets 42
A further parallel between chimpanzees and small scale human societies comes from analyses of
two extreme warring societies, the Waorani of New Zealand and the Yanomamo of Venezuela. Though
violence accounts for between 40-55% of all deaths in these two groups, attackers appeared immune to
injury, with no more than 5% dying in battle, and often no deaths at all. Chimpanzee attackers are
likewise immune to injury, due in large part to the strategic use of imbalances of power.
The parallels between chimpanzees and humans living in small scale societies supports the idea
that similar pressures favored the capacity for coalitionary killing in both species. Does this mean that
each of these species should always kill in this way, and thus, as argued by Ferguson, the archaeological
record should be chock full of deaths by coalitionary attackers? To argue for this position is to
misunderstand the nature of an adaptation, and the arguments put forth by Wrangham as well as the
evolutionary psychologists Martin Daly, Margo Wilson, and David Buss. As I discussed earlier on in this
chapter, adaptations are contingent upon particular environmental circumstances. What is adaptive today
need not be tomorrow. This is why it is not only unsurprising to see variation in the frequency of
coalitionary killing among chimpanzee sites, among humans living in small scale societies, and among
modern day humans who sometimes kill their spouses, stepchildren, and rivals, but predicted by
evolutionary theory. Adaptations are economically efficient solutions to particular social or ecological
problems. If those problems or pressures change, the original adaptation may have no impact on survival
or a negative impact. A hiatus in the archaeological record ⎯⎯ assuming this is the last word ⎯⎯ is
interesting with respect to the conditions that might favor or select against coalitionary killing, but in no
way undermines the logic of an evolutionary adaptation, one shared by chimpanzees and humans.
The second camp arguing against the parallels between humans and chimpanzees is defended by
the economist Samuel Bowles and his colleagues. Unlike the anthropologists, Bowles is entirely
sympathetic to biology but sees fundamental differences in the pattern of human killing and warfare. To
explain these differences he invokes two important attributes of human societies that have only weak
parallels in other species: large scale cooperation with unrelated others from the same group, together
with hatred, symbolic labeling, and the motivation to hurt all others outside the group. These two factors,
what Bowles calls parochial altruism, may have paradoxically generated both greater levels of
cooperation within groups and higher rates of warfare between groups. Those groups with the best
cooperators acquired the greatest resources and experienced the fewest losses due to cheaters and other
morally corrosive rogues. This power and inward-looking favoritism led to self-defensive emotions and
behaviors, ultimately leading to lethal aggression toward those with different beliefs and values. Thus
parochialism and altruism co-evolved, hand in hand, breeding prejudice as a result of group safety. This
evolutionary handshake resulted in warfare and our unique capacity as killers.
Bowles’ analysis is interesting and consistent with my explanation of how we evolved the
Hauser Chapter 1. Nature’s secrets 43
capacity for evil. For both Bowles and I, certain aspects of our capacity to harm others emerges as an
incidental byproduct of other capacities, and once this dynamic emerges, the combination of these
capacities can evolve and change. What Bowles’ analysis misses, however, is the fact that parochial
altruism could well be true, and so too could our shared capacity for killing with chimpanzees. As noted
above, rates of killing among chimpanzees and several small scale societies are comparable, and so too
are the costs and benefits to attackers and victims. This argues in favor of a shared history, and a shared
adaptation. It does not mean that all aspects of killing in humans are similar, or that the human mind froze
in a chimpanzee state with regard to its capacity to kill. It most definitely did not freeze.
Unlike the lethal attacks by chimpanzees that are restricted to cases where groups attack lone
victims, primarily from neighboring groups, we wreak havoc on a massive scale, with one on one, many
against many, and one against many, including victims within and outside our core group. Unlike
chimpanzees, even our young children have an appetite for violence that can be nurtured, as evidenced by
the brutality of child soldiers around the globe. Unlike chimpanzees, individuals will sacrifice themselves
for an entire group as evidenced most recently by suicide bombers in the Middle East. Unlike
chimpanzees, we derive great pleasure from watching others suffer, from watching violent movies, seeing
other animals fight, and imagining the decimation of an enemy. Our minds also generate ideological
reasons to motivate violence at extraordinary scales ⎯⎯ again, think of suicide bombers taking their lives
for a God, as well as the reward of an idyllic afterlife. And when our minds break down, or when we are
afflicted with particular disorders early in life, we are capable of experiencing bizarre appetites for
violence, including the joy of eating the flesh of murdered victims, having intercourse with dead bodies,
and asking for bondage and whippings to enhance sexual pleasure. These novel and unanticipated ways
of harming others are the result of new hardware that has evolved only once in the history of this planet.
HARMING OTHERS, version 2.0: requires Homo sapiens hardware
We depart from the pattern of adulticide seen in other animals because of our promiscuous brain. The
idea is not that our brains evolved for killing in these unique ways, but rather, that our unique style of
thinking led to novel ways of harming as an incidental consequence. The hardware that is our brain
enabled new ways of harming others, building on specialized adaptations, some shared with other species
and some uniquely human. The result is a brain that can develop a peculiar appetite for harming others.
To see how version 2.0 runs on our distinctively human hardware, let’s return to some of the core
microcontrollers that I discussed a few sections back. Recall that there are hormones like testosterone
that surge when individuals win a competition, whether this involves the physical fighting of deer using
Hauser Chapter 1. Nature’s secrets 44
their antlers, humans using their fists, or chess masters using their minds. Along with testosterone’s
increase is an increase in dopamine, a decrease in cortisol and serotonin, and a decrease in frontal lobe
activity and control. Within the environment of a promiscuous brain, this physiological ballet affects our
sense of fairness, empathy, moral conscience, attitude toward retribution and justice, as well our
willingness to engage in lethal aggression.
Brain imaging studies reveal that the prefrontal cortex plays an essential role in regulating our
aggressive instincts, when it’s working. When individuals respond aggressively to an unfair offer in a
bargaining game, testosterone levels rise and activity decreases in a part of the prefrontal cortex
associated with self-control. Thus, testosterone’s effectiveness in human aggression is facilitated by a
loss of control. Damage within this region of the brain causes abnormal aggressive responses to not only
direct insult, but even such trivial matters as being offered a lowish offer in the ultimatum game discussed
earlier. Anatomical and functional abnormalities within this region of the frontal lobes are also associated
with aggressive pathology, such as psychopathology. There are also individual differences in aggressive
tendencies among healthy people, due in part to differences in the patterns of activity between the right
and left prefrontal cortices. Heightened activity on the left is associated with greater sensitivity to reward,
lowered sensitivity to punishment, and considerably stronger aggressive responses to threatening stimuli,
such as an angry face. This is not simply a correlation, as evidenced by studies that experimentally either
suppress or increase activity in one hemisphere compared with the other. For example, if you contract
your right hand you will increase activity in the left hemisphere of the brain; conversely, contracting the
left hand increases activity in the right hemisphere. Subjects contracting the right hand in an
experimental setting showed more aggressive responses to insult than did subjects contracting the left
hand. The next time someone shakes a fist at you, check whether it is the right or left hand. If the person
is from a different group and holds a fundamentally different suite of ideological beliefs, which hand is
clenched is the least of your worries.
Favoritism toward those who are like us, combined with hatred toward those who are not, is
common in animals. As noted above, in-group favoritism or parochialism can lead to heightened levels of
cooperation within groups, while simultaneously increasing the level of hostility towards those outside.
Our promiscuous brain facilitated this co-evolutionary process, inviting the hormone oxytocin into the
mix. Among mammals, including humans, oxytocin is released in females during labor and breastfeeding,
and in both males and females during social bonding and parenting. This has led many to think of
oxytocin as the cuddle hormone or love drug. Floating within the human brain, oxytocin boosts trust in
games of cooperation, and greatly increases our ethnocentric biases. The Dutch psychologist Carsten De
Dreu and his colleagues ran a series of experiments that required male subjects to spray oxytocin or a
control up their noses. When oxytocin shoots up the nose, it goes straight to the brain. Relative to the
Hauser Chapter 1. Nature’s secrets 45
control group, those who sniffed oxytocin perceived in-group members as more likeable, more human,
more richly endowed with social emotions such as embarrassment, contempt, humiliation and admiration,
and more worthy of saving in an emergency. Oxytocin increases our sense of camaraderie toward those
within the inner sanctum, which can result in greater animosity toward those outside. Oxytocin may
therefore facilitate our ability to take out the competition even if this means killing another human being.
Oxytocin is two-faced, cuddling with its left profile and harming with its right.
This is a small sampling of the ways in which our promiscuous brain enables new forms of harm,
including killing other adults. We didn’t invent lethal aggression. We share this capacity with a small
group of animals that also kill other adults. But whereas these other species typically restrict their lethal
attacks to situations in which one group greatly outnumbers another, typically targeting adults from a
neighboring group, we evolved far beyond this monogamous approach. We adopted the cost-benefit
analysis that drives killing in other animals and applied it to killing in a virtually limitless space of
homicidal opportunities. We kill when we outnumber our opponents or are outnumbered by them,
attacking individuals within and outside our core group. We kill spouses, ex-lovers, stepchildren, those
who believe in God and those who don’t, the wealthy and the poor, kin and non-kin, and even ourselves if
the cause is good enough. Virtually anything goes.
Our promiscuous brains opened a Pandora’s box of harmful means, including the capacity to
address a multitude of injustices. This is a capacity that is inherently good, but incidentally bad. It is a
capacity that evolved in response to growing pressures to balance inequities and take care of those who
attempt to cheat society. It is a capacity that enabled us to engage in punishment in a broad range of
contexts, righting wrongs and opening a new path to feeling good about harming others.
Incidental justice
Cooperation is ubiquitous in the animal kingdom, occurring in a wide range of situations.
Humans are no exception. Like ants, humans also bring resources to their queen ⎯⎯ think England. Like
scrub jays, humans work with extended family members to rear the next generation of offspring ⎯⎯ think
Mormons. Like dolphins, human males form super-coalitions to gain access to females ⎯⎯ think the
Yanomami Indians of South America, where men raid neighboring villages to take their women. And like
chimpanzees, humans cooperate to monitor their borders, often capturing and killing intruders ⎯⎯ think
Palestine and Israel. But human cooperation is distinctive in two ways: we frequently cooperate with
Hauser Chapter 1. Nature’s secrets 46
large numbers of genetically unrelated strangers, and punish those who cheat by free-riding on others’
good will.
The challenge to any cooperative enterprise is to avoid getting suckered by free-riders who cheat
and add little or no help. As group size grows, the opportunity to cheat and get away with it grows as
well given the challenges of storing information about reputation. How do individuals and groups avoid
this sucker problem?
When nonhuman animals cooperate with members of the same species, they typically target kin.
Helping kin provides a buffer against the sucker’s costs because investing in kin means investing in
genetic posterity. Helping relatives, even at a cost, translates to helping ones genes move on into the next
generation ⎯⎯ an insight developed by the British evolutionary biologist William D. Hamilton. When
cooperation involves unrelated others, nonhuman animals attempt to circumvent the sucker’s problem by
working with a small number of familiar others whose reputation is known, targeting contexts where all
participants benefit more from working cooperatively than working alone. These mutual benefits help
offset the costs of cooperation.
By restricting cooperation to relatives or small numbers of unrelated but familiar group members,
animal societies have buffered themselves from extreme cheating. This is significant because cheaters
arise in a variety of contexts where there are rules of engagement, including both cooperative and noncooperative
situations. For example, both lions and chimpanzees cooperate in group defense against
dangerous neighbors. Some individuals cheat by lagging behind, or failing to join in altogether. In
societies organized around hierarchies, low ranking animals sometimes cheat by attempting to eat more
than their fare share or by reproducing when their societal norms explicitly forbid it. Interestingly,
cheaters in cooperative situations such as those in lions and chimpanzees, never suffer any adverse
consequences from the dominants. In contrast, cheaters in competitive situations such as those that arise
in hierarchical societies, are punished. Nonhuman animals thus have the capacity to recognize and
change rule breakers. And yet, these capacities are not applied in the context of cooperative interactions.
Monogamous thinking rules.
When it comes to enforcing fairness in cooperation, the fundamental barrier for animals lies with
the economics of punishment. Punishment is costly. When a cheater is detected and attacked, there is
always the possibility that he will retaliate. Cheaters, even when caught, need not surrender without a
fight. Punishment therefore requires the capacity to surmount an immediate cost, while recognizing the
possibility that any benefit could be greatly delayed. For example, lashing out against a lion laggard or a
chimpanzee cheater might cause each to join in on future cooperative ventures, but this is a delayed
benefit, and it may never materialize. This adds another potential opportunity cost. As Shakespeare so
deftly noted “Defer no time, delays have dangerous ends.”
Hauser Chapter 1. Nature’s secrets 47
Waiting for a future benefit, whatever its currency, is hard for all animals, humans included.
Studies of rats, birds, monkeys, apes, human children and adults show that individuals perceive future
gains as less valuable than immediate, but smaller gains. For example, give any one of these animals a
choice between one piece of food and ten, and they will pick the ten. More is better than less, except if
you are a dieting human. Now give them a choice between one piece available immediately and ten pieces
available after some delay. Virtually every animal shifts to the one piece, with the only comparative
difference linked to the length of the delay ⎯⎯ a few seconds for rats, birds, most monkeys, young
children, and adults with frontal lobe damage, a few minutes for some apes, older children and some
adults. Everyone is, to some extent, pulled by the hedonistic now. The future loses its luster when a tasty
alternative is just within reach. This is in part due to the uncertainty associated with the future, and in
part, the sheer temptation to take what is in front of us.
Unique evolutionary changes in the human brain allowed us to exert much greater patience,
overriding the pull of the hedonistic now. These changes didn’t evolve for punishment, but they were
readily deployed by this system of justice. We rely on creative strategies to place value on the future,
including putting resources away so that we can’t use them ⎯⎯ think savings accounts ⎯⎯ and making
verbal commitments that bind us to the future ⎯⎯ think about the social embarrassment of failing in front
of friends. These strategies help diminish the emotional pull of taking what is immediately available,
allowing future benefits to gain in attractiveness. This is a brain that can wait for the delayed benefits of
punishment.
The brain changes that facilitated our capacity to delay gratification were accompanied by others
that further offset the costs of punishment: our brains reward us with a feel-good feeling when we pay the
costs of punishment. For the first time in evolutionary history, the physical and psychological costs of
punishment were at least partially offset by the pleasure of justice served, whether delivered directly or
witnessed from afar.
When we punish or get even with those who have acted badly, we feel a hedonic high, an
experience captured by the metaphor “revenge is sweet but not fattening.” As demonstrated by the
economist Ernst Fehr, this is more than a metaphor. When we hand someone his just deserts, punishing
someone for cheating, lying, or breaking a promise, our brain responds as if we handed ourselves just
desserts, activating brain circuitry associated with reward. In one study, two subjects played a monetary
exchange game in which one player ⎯⎯ the donor ⎯⎯ decided how much of a pot of money to give to
another. A third player observed, out of view, the outcome of the exchange. In some cases, observers
witnessed a fair division of the money and in other cases, an unfair division in which the donor kept a
disproportionate amount of the total. The observer then faced a difficult decision: leave the two players
with their take-home earnings or use personal funds to take away money from the donor, returning it to
Hauser Chapter 1. Nature’s secrets 48
the bank. Taking money away from the donor is a form of costly punishment. It is costly in two ways: the
punisher loses money he could have kept, and the donor loses money that he unfairly kept in his previous
exchange.
When donors kept a significantly larger portion of the original sum, observers punished, paying
the costs. They also reported feeling good about taking down the cheapskates. Where was this honey hit
to the brain coming from?
To figure this out, Fehr and his colleagues put people in a brain scanner and used a technique
called Positron Emission Tomography or PET. This type of scanning provides a picture of how much
glucose is used up by different brain areas during a task. Higher glucose consumption occurs when there
is higher activity in a brain region. When punishers decided to punish a selfish donor, glucose
consumption increased in a region of the brain associated with reward: the dorsal striatum. This region is
also active when you eat ice cream, earn money, and solve an unexpected problem. Punishers incurred a
financial cost, but gained emotional elation and internal reward. It turns out that giving someone his just
deserts feels like eating dessert, but without the caloric gain.
When distinctively promiscuous punishment evolved, it transformed our capacity to cooperate
and to maintain conformity to social norms. It provided us with the tools to not only repair a puncture in
the system of norms, but to feel good about the costs personally incurred. When we punish, we have
served justice and served ourselves a helping of the brain’s rewards. The fossil record doesn’t capture
when we evolved the capacity to punish, as skulls and bones, stone tools, and even paintings are silent on
why someone received a spear through the head ⎯⎯ perhaps punished for a wrong doing or perhaps an
enemy, a competitor interested in the same resources, or a suspected lover. No one will ever know. What
we do know is that other primates never punish cheaters who break the norms of cooperation, whereas
hunter-gatherers dotting the continents do. Though people living today as hunter-gatherers are not perfect
replicas of what life was like way back when, they indicate that before we had sophisticated technology,
agriculture, and permanent residences, we had the capacity to minimize the costs of the sucker’s problem.
Whenever this capacity emerged in human evolution, it provided a critical part of the solution to the
problem of large-scale cooperation among unrelated strangers. With many eyes on the look out for
cheaters, and a capacity to take out or ostracize the free riders, cooperation emerged as a stable solution to
problems that are unsolvable at an individual level, including group defense and the acquisition of costly
resources. Punishment enabled humans to live in large, stable cooperative societies, many of whom are
unrelated strangers.
This momentous event in the history of cooperation carried with it a serious cost, bringing
aggression and reward into closer proximity, with the costs of attacking others overshadowed by the
benefits. As I discuss in greater detail in the next chapter, this economic transformation created, as an
Hauser Chapter 1. Nature’s secrets 49
incidental consequence, a hunger to watch violence and to see it as entertainment. It allowed our feelings
of inequity and envy to morph into schadenfreude, retaliation, and spite. It allowed us to enjoy violence
as perpetrators and spectators. It allowed us to put our money on feeling good about righting an injustice.
Why oh why?
Why did evil, expressed as excessive harm to innocent others, evolve? The answer lies, so I suggest, in a
special property of the human brain. Some time after we diverged from a chimpanzee-like common
ancestor, the human brain was remodeled to allow promiscuous connections between previously
unconnected circuits. Promiscuity enabled us to explore new problems using a combination of older, but
nonetheless adaptive parts. Some of these novel explorations led to highly adaptive consequences, as
when we developed the ability to self-deceive in the service of pumping ourselves up to do better in the
context of competition; or when we invented new technologies to solve difficult environmental problems,
such as using spears to capture prey at a distance; or, when we acquired the know-how to stockpile and
enhance resources such as food, water and fertile land that are critical to individual survival and
reproduction; or when we evolved the richly textured social emotions of jealousy, shame, guilt, elation,
and empathy, feelings that motivate individuals to recognize the importance of others’ well-being and
interests and to correct prior wrongs; or, when we tapped into the rich connection between reward and
aggression to punish cheaters trying to destabilize a cooperative society. But these same adaptive
explorations also resulted in incidental costs that have destroyed the lives of innocent individuals. The
capacity to deny others’ moral worth enabled us to justify great harms, including self-sacrifice as living
bombs designed to annihilate thousands of non-believers. The capacity to create advanced weaponry
enabled us to kill at a distance, thereby avoiding the aversiveness of taking out those staring back. The
capacity to stockpile resources led to the growth of greed, increasing disparities among members of
society, the inspiration to steal, and heightened violence both to defend and to obtain. The capacity to
experience social emotions such as jealousy led to blind rage and a driving engine of homicide, including
cuckolded lovers who kill their spouses and stepparents who kill their stepchildren. The capacity to feel
good about harming others enabled us to recruit this elixir in the service of causing excessive harm in any
number of novel contexts, from ethnic cleansings to bizarre fetishes that include self-mutilation. And the
list goes on. This is the yin and yang of promiscuous thinking. This is the natural history of evil, its
ancestry and adaptive significance. This evolutionary explanation sets the stage for unpacking the recipe
for evil, how it develops within individuals and societies, ingredient by ingredient.
Hauser Chapter 1. Nature’s secrets 50
Endnotes: Chapter 1
Recommended books
Bloom, P. (2010). How Pleasure Works. New York, Norton Press.
Coyne, J. A. (2009). Why Evolution is True. New York, Viking Press.
French, P. (2001). The Virtues of Vengeance. University of Kansas Press.
Goldhagen, D.J. (2009). Worse than War. New York, Public Affairs.
Kekes, J. (2005) The Roots of Evil. Ithaca, Cornell University Press.
Kiernan, B. (2007). Blood and Soil: A World History of Genocide and Extermination from Sparta to
Darfur. New Haven, Yale University Press.
McCullough, M.E. (2008). Beyond Revenge. John Wiley & Sons.
Pinker, S. (2011) The Better Angels of Our Nature. New York, Viking Press
Wrangham, R.W., & Peterson, D. (1996). Demonic Males: Apes and the Origins of Human Violence.
Boston, Houghton-Mifflin.
Notes:
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pace of life under artificial selection: personality, energy expenditure, and longevity are
correlated in domestic dogs. American Naturalist 175(6), 753–758.
• What’s religion for? Boyer, P. (2001). Religion explained: The evolutionary origins of religious thought.
New York, Basic Books; Wilson, D.S. (2002). Darwin's Cathedral. Chicago: University of
Chicago Press; Sosis, R., & Bressler, E.R. (2003). Cooperation and commune longevity: a test of
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& Shariff, A. F. (2008). The origin and evolution of religious prosociality. Science, 322(5898),
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58-62; Banerjee, K., Huebner, B, & Hauser, M.D. (2010). Intuitive Moral Judgments are Robust
across Variation in Gender, Education, Politics and Religion: A Large-Scale Web-Based Study.
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fairness and punishment. Science 327(5972), 1480-1484; Pyysiäinen, I., & Hauser, M. (2010).
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6; Sosis, R. (2009). The adaptationist-byproduct debate on the evolution of religion: Five
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• Evil wasps, monogamous thinking, and Darwin’s worry: Haspel, G., & Libersat, F. (2004). Wasp
manipulates cockroach behavior by injecting venom cocktail into prey central nervous system.
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T.M., Gols, R., Nakamatsu, Y., & Tanaka, T. (2008). Comparing the physiological effects and
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(2007). Factors affecting spider prey selection by Sceliphron mud-dauber wasps (Hymenoptera:
Sphecidae) in northern Italy. Animal Biology, 57(1), 11-28.
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Iromenga, M.(2009). Life histories, blood revenge, and reproductive success among the Waorani
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Hauser Chapter 1. Nature’s secrets 53
• The evolution of cooperation and punishment in animals: Clutton-Brock, T.H (2009). Cooperation
between non-kin in animal societies. Nature, 462, 51-57; Clutton-Brock, T.H., & Parker, G.A.
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Stevens, J.R, & Hauser, M.D. (2004). Why be nice? Psychological constraints on the evolution of
cooperation. Trends in Cognitive Sciences, 8(2), 60-65.
• Cooperation, punishment, and feeling good, see: Boyd, R, Gintis, H, & Bowles, S. (2010). Coordinated
punishment of defectors sustains cooperation and can proliferate when rare. Science, 328(5978),
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& Richerson, P.J. (1992). Punishment allows the evolution of cooperation (or anything else) in
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McElreath, R., Barr, A., Ensminger, J., Barrett, C., Bolyantz, A., Ziker, J. (2006). Costly
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Quotes
Watts, D. P., Muller, M., Amsler, S. J., Mbabazi, G., & Mitani, J. C. (2006). Lethal intergroup aggression
by chimpanzees in Kibale National Park, Uganda. American journal of primatology, 68(2), 161–180;
quote: p.g., 166
Seville Statement on Violence, Spain, 1986: http://portal.unesco.org/education/en/ev.php-
URL_ID=3247&URL_DO=DO_TOPIC&URL_SECTION=201.html
Ferguson, R. B. (2006). Tribal, “Ethnic,” and Global. In: The Psychology of Resolving Global Conflict:
From war to peace, volume 1, Nature vs Nurture (Ed. M. Fitzduff, C.E. Stout; Lawrence Erlbaum Ass),
1–15.; quote: p.g. 45
Hauser Chapter 1. Nature’s secrets 54
Chapter 2:
Runaway desire
The desire of being believed, or the desire of persuading, of leading and
directing other people, seems to be one of the strongest of all of our desires.
⎯⎯ Adam Smith
In 1999, an investment officer in a management firm had a gut feeling that something was wrong in a
corner of the securities market. Based on calculations from the stated investment strategy for the fund, the
returns were not only orbiting outside the financial stratosphere, but were mathematically impossible. The
officer contacted the Securities and Exchange Commission, outlined the problem, and asked them to look
into it. No reply. Year after year, the officer continued to contact the SEC about this case, explaining that
it was potentially lethal, that he had no personal investments in the fund, and had never been an
employee. No reply. Then, in 2007, he sent the SEC a 17-page report, showing why there was only one
plausible conclusion: the stated strategy for the fund was a fraudulent cover up for a massive moneymaking
scheme. Eventually, in 2008, the brains behind this scheme was ousted, escorted to a life in prison
as number 61727-054, and welcomed to his new home by a community of like-minded white-collar
criminals.
Meet HARRY MARKOPOLOS ⎯⎯ the investment officer ⎯⎯ MADOFF SECURITIES ⎯⎯ the seductive
investment opportunity ⎯⎯ and BERNARD MADOFF ⎯⎯ the genius behind one of the most spectacular
Ponzi schemes in recorded history. Whistleblowers started warning the SEC as early as 1992, but no one
listened. Madoff was making money hand over fist by pocketing new investments and if needed, using
some of these to pay off individuals wishing to redeem their funds. Ponzi schemes work as long as new
investments exceed the number of investors wishing to redeem their own investments. And for Madoff,
this balancing act worked for 16 years. Then, as in the Bible’s Book of Joshua, the walls came tumbling
down, with Jericho riding in to hand Madoff a 150-year prison term for the financial murder of his
trusting clients. Altogether, these innocent and trusting people lost approximately $65 billion dollars, all
because one man allowed his desire for wealth and power to run out of control. Or so it seemed.
Hauser Chapter 2. Runaway desire 55
Were those who put their money in Madoff securities entirely innocent? Or, like Madoff, did
they too allow their desire for more wealth to run wild? Was Madoff’s desire for extreme wealth that far
off the curve of human variation? And if he was off, who or what do we blame? Could some quirky
feature of Madoff’s genome, together with the brain states it orchestrates, have pushed him over the edge
into a universe of unreasonable and even irrational desires? Does it matter that Madoff grew up in a world
in which the rich get richer despite the direct or indirect harm caused to innocent others?
Many have speculated answers to these questions, based on little or no evidence, and certainly no
scientific evidence. But what matters most about case studies such as this is that they raise the kinds of
questions that science can answer. What matters is that it is possible to run a Ponzi scheme. It is possible
because there are humans like Madoff who are driven by the desire to accumulate great wealth, despite
the personal risks and costs to others. It is possible because the world is populated by people who are
willing to throw critical reasoning to the wind in the face of a tempting offer to make a huge amount of
money. It is possible because people will take risks either without considering the potentially horrific
consequences to innocent others, or by trivializing them.
As far as we know, Madoff never intended to put his friends and family members in a state of
financial ruin. As far as we know, many invested in his securities knowing that investments can fail. As
far as we know, some must have been suspicious, at least for a while, about how their investments could
consistently yield such over the top returns when nothing else has or seemingly could. Madoff is certainly
to blame for creating a fraudulent investment opportunity, but so too are the many who trusted him
without question, happy to make absurdly high returns.
Did Madoff cause excessive harm? Yes. Were those harmed innocent victims? Not entirely.
None were forced to invest, and all invested with at least some knowledge that the promised returns were
off the charts. This is not innocence. This is desire run amuck while self-control and reason fly standby.
Madoff was morally wrong, but not evil, at least not on my accounting of the ingredients of evil.
Madoff’s case illustrates the power of desire to stampede reason. As the essayist James Thurber
remarked, “Love is blind, but desire just doesn’t give a good goddamn.” Madoff didn’t give a good
goddamn. How does a system like this get going, and then sometimes go wrong, very wrong? It all starts
with the elements of pleasure.
P for pleasure
Imagine that scientists have just announced the discovery of a center in the brain that manages our
experience of pleasure. Imagine further that they have invented a consumer device that, for only $49.99,
Hauser Chapter 2. Runaway desire 56
enables you to ramp up or down the activity in the pleasure center. Want to get a bit more out of your
dinner, a movie, tennis stroke, work, or sex? Flip the switch. Want to buffer yourself from the pain of
ostracism, a romantic break up, or a colonoscopy? Flip the switch. Would you buy it? If so, what would
you use it for, and would you be a habitual user? Would you worry about any side effects? Might using
this device become addictive, or worse, either destroy the feeling of pleasure altogether or push you into a
never-ending quest for satisfaction, with each dollop of pleasure leaving you wanting a bigger dollop next
time around. This may seem like science fiction, but it’s closer to non-fiction.
Over fifty years ago, scientists working with rats, implanted electrodes into in a region of the
brain called the nucleus accumbens. The electrodes were connected to a switch. If the rat pressed the
switch, it activated the electrode and thus stimulated this brain area. The rats indeed pressed, over and
over again, some at a rate of 2000 presses per hour, with no external reward or threat of punishment.
Pressing the switch was the reward, or at least the vehicle to what appeared to be the experience of
reward. Pressing the switch was addictive. These scientists had discovered a critical part of the circuitry
of pleasure, in rats! The rats discovered a pleasure switch, something they wanted to experience over and
over and over again.
Soon after this discovery, clinicians started using deep brain stimulation to treat individuals with
neurological complications, including Parkinson’s patients suffering from loss of motor control, patients
experiencing sustained pain, Tourette’s patients suffering from motor tics and obsessive-compulsive
problems, and even a patient in a coma who had lost, but then slowly recovered the capacity to name and
grasp objects. Similar to the rat work, the technique involves implanting an electrical pulse generator
within a targeted brain region. When the generator is turned on, it stimulates activity in previously
malfunctioning regions. But as with genetic manipulations and the unknown space that characterizes the
genomic universe, so too is the situation unchartered in the neuronal universe. Two patients suffering
from chronic pain were implanted with impulse generators and subsequently developed profound
addictions to the stimulation. In addition to relatively successful pain reduction, both patients experienced
an enhanced desire for sex, including erotic feelings. One of these patients self-stimulated so often that
she forgot to wash, change clothes, and adhere to family commitments. What happened? Did the
clinicians treating these patients hit the pleasure center? When stimulated, what actually changed in the
minds of these patients? Did they simply want more sexual arousal, suggesting that stimulation turned up
the gain on their desire for sex? Or, did stimulation change what they like, a shift in the sense of pleasure
that accompanies sex, and in this case, the anticipation of sex? Or perhaps it changed both wanting and
liking, especially since we often want things we like?
These observations of how humans and rats respond to brain stimulation show that particular
areas of the brain are linked to pleasure, especially the motivation to obtain rewarding experiences. These
Hauser Chapter 2. Runaway desire 57
observations also reveal that when these areas are activated, they can result in addictive, uncontrollable
behaviors that are toxic to self and others. They suggest that areas of the brain associated with desire can
run out of control. But to understand how the brain motivates us to want some things but not others, how
it creates the experience of liking, and how it enables us to want things we like by learning about the
world, we must turn to experiments on nonhuman animals, brain scans of healthy humans, the mechanics
of mind-altering drugs, conscious and unconscious influences on our choices, and the sad stories of
individuals with uncontrollable urges to eat, drink, snort, shoot up, and gamble. This is the evidence that
scientists, especially the American cognitive neuroscientist Kent Berridge, have gathered to explain the
three core elements of pleasure: wanting, liking, and learning.
Often, but not always, the experiences we want or desire are the experiences we like. Often, but
not always, the experiences we like are rewarding and good for our health. Often, but not always, we are
aware of the experiences we like, and make rational plans to experience them again. Often, but not
always, our rational plans to experience what we like makes us happy. Often, but not always, we find
ways to maintain our happiness by using self-control to moderate our exposure to pleasurable
experiences. The often refrain refers to the fact that the systems involved in wanting, liking, and learning
work in this way most of the time. The but not always refrain is a tip off to exceptions that speak to
interesting aspects of the machinery. For example, though we most often want things we like, we can
want things we don’t like and like things we don’t want. I want to lift weights, do push-ups and sit-ups to
stay fit, but I don’t really like doing any of these exercises. I like the Porsche Boxster sportscar, but don’t
want one because it is a gas guzzling environmental nightmare and inconveniently small for a family car.
The fact that wanting and liking can mount a unified front or conflict with each other shows that it is
important to look at the glue between them, which is learning. Learning allows us to work out our values,
setting up a preference profile for what we desire in the people we interact with, the places we visit, the
objects we handle, and the events we experience. Learning allows us to predict situations that generate
pleasure or pain. Though we are conscious of many of these processes, and can actively influence them,
unconscious processes are also at work. These systems of the brain link us to our evolutionary past, and to
animals without language but clearly expressed likes and dislikes.
Evolution has endowed all animals with unconscious wanting systems ⎯⎯ brain circuitry that
motivates individuals to seek resources that enable survival and reproduction. For young mammals, still
dependent upon parental care, their desires are simple: milk and warmth from their mothers, and
depending on the species, additional warmth and protection from fathers; for the record, the human father
is an oddity among primates, as no other ape and virtually no other monkeys express a paternal instinct.
With growth and independence, desires shift to other resources that can satisfy hunger and thirst,
accompanied by sexual and social status desires. Though driven by unconscious operations, the behaviors
Hauser Chapter 2. Runaway desire 58
that result are often strategic, dependent upon changes in climate, other competitors, who happens to be in
a bad mood, and who is sexually active. In a variety of species, from dung beetles to deer, biologists have
developed mathematical models that accurately predict how long an individual should wait for a sexual
partner or feed in a food patch. The accuracy of these models shows that individuals’ desires for resources
linked to survival and reproduction are captured by lawful principles or rules. This is important because it
means we understand how the machine underlying behavior works. It means we understand how animals
make certain choices.
Understanding how wanting works is straightforward. In both humans and nonhuman animals,
we can measure what individuals approach when we give them a choice, as well as how much effort they
are willing to exert while approaching and gaining access to a particular object or experience. For
example, in studies that explore whether captive animals are provided with sufficient housing conditions,
an experimenter presents individuals with a choice of rooms, one consisting of the typical housing
environment and the others by the addition of goods believed to be of interest. To enter a given room
requires opening a door. To determine how much an individual really wants what is in another room, the
experimenter ramped up the difficulty of opening each door. In studies of captive hens and mongoose,
individuals exerted considerable effort to open some doors but not others. Hens rammed into doors
opening onto a chipped wood floor, whereas mongoose did the same for a pool of water. These are items
they want, but do not get in captivity.
What about liking? It may seem, at first blush, that because liking is a subjective experience, that
there are no clear objective ways to measure it. My likes are my own. You can’t possibly know what it
is like to be me. If you can’t know what it is like to be me, then we can’t possibly know what it is like to
be a mongoose, mouse or monkey. There are, however, ways of measuring liking and disliking that are
reliable, objective, and consistent across species. In many animals, including human babies who can’t
speak and human adults who have lost this capacity due to brain injury, there are distinctive behaviors
that are consistently linked to positive experiences and others linked to negative ones. For example, in
mice, monkeys, and human babies, tasting something sweet like sugar causes a lot of lip licking, whereas
tasting something bitter such as quinine causes mouth gaping, nose twitching, and arm flailing. These
similarities show that evolution has been conservative, maintaining the same underlying mechanisms for
handling likes and dislikes. These similarities have enabled scientists to understand how the brain systems
involved in wanting and liking can change together or separately, even though they can’t help us
understand the harder problem of what, in particular, it is like for a given mouse, monkey or man to like
something.
To understand the machinery that drives rodent wants or desire, Susana Peciña and Kent Berridge
took advantage of the genetic technique that Joe Tsien ⎯⎯mentioned in the last chapter ⎯⎯ used to create
Hauser Chapter 2. Runaway desire 59
smart mice. Recall that Tsien jazzed up a gene’s expression to improve memory and learning. In
contrast, Peciña and Berridge quieted a gene that controls the amount of dopamine floating around in
between neurons. With this gene silenced, dopamine levels increased. Compared with normal mice, these
dopamine-plus mice consumed twice as much food and water, and learned much faster where food was
located within a maze. But when it came to measuring licking as liking, the dopamine-plus mice were no
different from normal mice. Dopamine is therefore essential for the wanting system, but not the liking
system. This conclusion has been supported by many other studies, of mice and men, in the context of
eating and drug addiction ⎯⎯ two topics that I will shortly revisit.
To understand what rodents like, Peciña and Berridge injected an opioid drug ⎯⎯ similar to opium
from poppy plants ⎯⎯ into two brain regions associated with reward ⎯⎯ the nucleus accumbens and the
ventral pallidum. Not only have studies of rodents, monkeys, and humans revealed that these areas are
associated with reward ⎯⎯ recall the brain stimulation studies ⎯⎯ but they contain sub-regions known as
hedonic hotspots ⎯⎯ zones tuned to particular kinds of stimulation, designed to jazz up the liking element
of pleasure. Following injection, individuals licked four times more often in response to sugar as the noninjected
individuals, but did not show a difference in wanting. The opioid injections also caused a
decrease in the aversiveness of bitter quinine, as evidenced by a decrease in mouth gaping. Turning on
these hedonic hotspot ramped up the pleasure of sweets, and diminished the displeasure from bitters.
Together, the Pecina and Berridge studies highlight the independence of wanting and liking, and the ways
in which the brain ⎯⎯ or a clever experimenter playing with it ⎯⎯ regulates the elements of pleasure.
How does the brain figure out what’s hot and what’s not, delicious or disgusting? It’s one thing
to desire a particular experience, and another to derive pleasure from the experience. But the world is not
set up with labels that indicate which objects and events are pleasurable and which distasteful. Every
object and event has particular properties that, depending on the animal’s sensory ability, can be seen,
heard, tasted, smelled, or touched. For all organisms, there are receptors within each of the sensory
modalities that are biased to prefer some things over others. This is why no human baby has to be taught
to dislike bitter things and like sweet things. From the very first encounter, sugary solutions trigger
tongue protrusions and licking, whereas bitter solutions trigger a gaping mouth. We have evolved, as have
other animals, sensory systems that are tuned to prefer some things and dislike others, right from the start.
These initial biases guide the learning process, facilitating acquisition of new knowledge in some cases,
making it almost impossible in others, and setting a course to self-destruction in yet others. Try teaching
a young child that the taste of sweet chocolate is disgusting while the taste of bitter endives is delicious.
Try teaching cocaine addicts to turn off the magnetic pull of white powder, or convincing alcoholics that
the clinking sound of ice in a glass isn’t meaningful. Try teaching rogue soldiers involved in genocide
Hauser Chapter 2. Runaway desire 60
that the parasitic enemy shouldn’t be exterminated. This is where scientific explanation gains
considerable interest, helping us understand how we develop anticipatory pleasures and past-oriented
regrets, struggle to change from habitual rewards, and acquire irrational desires for experiences we no
longer enjoy ⎯⎯ a problem that appears to maintain most forms of addiction.
Humans go to restaurants and bees to flowers because both are associated with food. Within these
broad categories, there are good restaurants and flowers, as well as bad ones, where good and bad are
determined by experience. The experience can be direct, as when food is actually consumed, or indirect
as when humans listen to an animated friend describe a restaurant’s menu and bees watch a hive mate
dance, providing a description of the flower’s location and quality. Once the association between food
and location is established, simply seeing the restaurant or flower triggers a cascade of neural and
chemical activity in the brain linked to reward and the anticipation of pleasure. The restaurant and
flower are cues that predict food. If you walked into your favorite restaurant and found that they sold
fertilizer rather than food, you would be heartbroken. If you haven’t been to the restaurant in a long time,
but memorialized your previous experience as a gastronomic high, you will be deeply disappointed if
your first bite doesn’t live up to the standards you anticipated. This mismatch between anticipated and
experienced reward will lead to a cascade of brain activity ⎯⎯ indicative of an error. The primary engine
driving the experience of reward, including predicting when it will occur and with what kind of intensity,
is the dopaminergic system, a network of brain areas that releases dopamine in most invertebrates and
vertebrates, including the human vertebrate.
Many natural behaviors trigger dopamine, including male songbirds singing to attract females,
rhesus monkeys seeing a red light that has been associated with a soon to be delivered shot of juice, and
humans cooperating with each other. Many unnatural behaviors and objects can also trigger dopamine.
Animals trained to press a switch for food, will often become obsessively attracted to the switch,
caressing and biting it even in the absence of food; humans with addictions to cigarettes, food and
gambling, will often obsessively fondle an empty cigarette carton, fork, and deck of cards, respectively.
But these correlations leave open the question of whether dopamine causes the anticipation or experience
of reward, or flows from these experiences.
To tackle the causality problem requires experiments, either directly changing dopamine
concentration or comparing individuals who, due to genetic differences, show differences in dopamine
levels. We know from studies of rodents and monkeys that selectively increasing dopamine with drugs
results in heightened wanting of food if there are cues to foraging, or sex if opportunity knocks. The
Israelian cognitive neuroscientist Tali Sharot pursued a similar approach with healthy humans subjects.
She first asked individuals to rate how happy they would be if they vacationed in 80 possible destinations.
Then, some subjects took a placebo while others took L-dopa, a drug that selectively increases the release
Hauser Chapter 2. Runaway desire 61
of dopamine. Later, these same subjects imagined what it would be like to actually vacation in these
places, and rated their imagined experience. Those on L-dopa felt they would be much happier, revealing
the power of dopamine to cause changes in our experience of reward. Complimenting these experimental
results are studies showing that genetic variation in the expression of dopamine in humans are closely tied
to impulsive behaviors and behavioral disorders. Thus, individuals with genetic variants that result in
higher levels of dopamine are more likely to engage in compulsive gambling and eating, leading to
addictions. The anticipation of heightened pleasure leads these gamblers, eaters, and abusers to want
more and more.
This work shows that dopamine is necessary for monitoring and guiding our desire for reward,
with evidence of individual differences that start with our biology. This is a highly adaptive system. But
changes in dopamine can also cause our desire for reward to runaway, like a brakeless trolley. This is a
highly maladaptive process. This flip between adaptive and maladaptive that we see within the
dopaminergic system is, by now, a familiar brain routine. It provides, I believe, the means to explain all
manners of excess, from the desire for food and money to drugs and violence.
Obesity and drug addiction are disorders of excess. They are disorders of insatiable desire. There
are many paths to obesity and addiction, but all ultimately point to changes in the reward system. In
humans born with deficient levels of the hormone leptin, overeating and obesity are common outcomes.
When these individuals view images of food during a brain scanning session, they show lower levels of
activity in the striatum than non-leptin deficient individuals. The striatum is an area that is rich in
dopamine and an essential part of the reward system. This may, at first, seem paradoxical: how could
those who eat to excess not show an excess of activity in the striatum, and thus, an over-the-top
experience of reward upon seeing food? The answer lies in studies of rodents and humans. Whether it is
obese rats or obese people, both show compulsive eating, but lower levels of expression of dopamine in
the striatum. If you silence a key dopamine gene in rats, you can quickly turn them into food junkies,
driven by an unsatisfied wanting system. Overeating, like over-drugging, turns the reward dial down.
This is an adaptive response, except when it operates in the mind of a food or drug junky. Though the
reward hits are small and unnoticeable, the wanting system remains highly motivated, triggered by the
same cues. What food and drug junkies want is more hits, but the reward system isn’t delivering. This
causes them to want even more.
What the work on obesity and addiction tell us is that independently of how people get started on
the path to fulfilling their desires, and whatever leads them to over-consume, consumption loses its luster.
The brain is smart: excess is bad and thus the reward systems turns off. But because the wanting or desire
system is independent from the reward system, and has evolved insurance against a complete shut down,
Hauser Chapter 2. Runaway desire 62
it continues to drive desire. Because the reward system isn’t delivering the goods, excess unfolds driven
by a wanting system that is looking for pleasure in all the wrong places.
When we were hunters and gatherers, excess was an unborn concept. We lived on the edge then,
enjoying scraps of whatever kill arrived on the fireplace, together with the tubers gathered up on the day.
We, at least many of us in the West, live in a world that has a 24/7 cafeteria of food and drugs. It is a want
it-have it culture. As work in molecular biology shows, and as I will pick up in chapter 4, some of us start
off more vulnerable than others, susceptible to sampling from the cafeteria at all hours of the day and
night. The combination of a heavily marketed environment and a biological susceptibility to excess, is a
losing combination for the consumer.
The work on addiction provides a template for thinking about how individuals and societies ignite
a path to excessive harms. In the same way that excessive eating gets going and going out of control
when the dopamine system drives an irrational desire to want more and more food that is liked less and
less, so too is excessive harm often driven by a similar decoupling between wants and likes. Individuals
start with a desire to acquire wealth, to physically harm those who are unlike them, or taste the sweetness
of revenge against someone who acted unfairly. These desires are often linked to an experience of
pleasure or the anticipation of pleasure. But as such actions and their consequences accumulate, the
pleasure derived diminishes, as money is acquired just for the sake of having more, while individuals are
injured, maimed, or killed because this is the policy that must be pursued. Liking is no longer part of the
equation, leaving cold desire to do its work at the expense of innocent others who get in the way.
To develop this idea, and especially the link to excessive harm, I have to fill in a missing piece in
our discussion of desire. Everything I have discussed in this section has focused on individuals and their
core corporal needs for survival ⎯⎯ or in the case of drugs, recreation. I haven’t said a word about how
desire works in the social arena, whether the same systems are in play when we compare our own desires
and resources with others, or with other opportunities. When desire is motivated by what others have or
have achieved, are the same processes in play as when we eat, drink, or gamble? These are important
questions as the desire to accumulate great wealth or to harm others is often motivated by comparison
shopping, assessing what others have relative to our own status. The most primal starting point for
comparison shopping is the world of hierarchies, a world where the desire to dominate rules.
Power hungry
Whether you are observing a social insect, fish, lizard, bird, rat, whale, monkey, or human, males are
bigger and bolder, more boisterous, brash and brazen, and more motivated to get into a brawl than
females. Though biologists don’t define the sexes based on these differences, they use them to understand
Hauser Chapter 2. Runaway desire 63
what drives competition for valuable resources and what determines the criteria for dominance status.
Biologists define the sexes based on differences in the gonads, the reproductive organs that generate eggs
and sperm, and the corresponding effects of sex-specific selection on the mind, body, and behavior.
Females are those with larger, more costly gonads, where cost is defined on the basis of how much energy
is invested in production. Think eggs versus sperm. This difference sets up an immediate competition,
especially for species that have parental care. Once you invest in a big expensive egg, you don’t want to
lose your investment. You want to protect it, avoiding harm and minimizing risk. On the other hand, if
your investment is small, you are not only freer to take risks, but favored to do so.
These ideas started with Charles Darwin. One hundred years later, they were developed in
exquisite detail by the American evolutionary biologist Robert Trivers. Combined, they provide an
explanation for why, in most species including our own, males compete with each other for access to
females ⎯⎯ the most valuable and limited resource ⎯⎯ and why females are picky, expressing an aesthetic
preference for males of a particular quality. Selection favors parts of the body and brain associated with
dominant males and picky females. Dominant males win fights against other males, and thus gain access
to females. Dominant males take risks and are more aggressive. Picky females hold out for the best males,
those who provide the most desirable resources. Picky females are patient, waiting for males with good
genes, access to prime real estate, and the protective skills and motivation to defend them and their young.
These are qualities linked to high status. These are qualities associated with the ability to obtain and
control resources. These are the qualities that females desire.
Male desire for dominance is therefore nurtured by female desire for dominant males. Like
appetites, these desires seek satisfaction. Like appetitive addictions that create devastating consequences
for individuals, groups and nations, so too can our appetite for domination.
Recall from the last chapter that testosterone and cortisol play a teeter-totter role in aggressive
competition. When testosterone is high and cortisol is low, the motivation to fight and defend one’s
resources is high. These two hormones, and the brain areas they impact, fuel the desire to maintain a
competitive edge. Recall further that winners experience an increase in testosterone, and losers a
decrease, and that testosterone is addictive. Testosterone is therefore part of the system that links the
desire to outcompete and gain dominance status with the rewarding experience of winning and achieving
high rank.
To attain high rank, including a competitive advantage over others with respect to food and
mating opportunities, requires social knowledge. How tough is the alpha baboon or boss in a company,
and what kind of support do they have from other individuals in the group? How sexually receptive are
females when their hormonal cycles tilt them into a period of potential conception? What other males are
interested in these females? Attaining and maintaining high rank also requires attention to cues that are
Hauser Chapter 2. Runaway desire 64
continuously changing, including where someone is looking and parts of the body that signal power and
sexual availability. The American neuroscientist Michael Platt carried out a clever series of experiments
to understand how much male rhesus monkeys value different kinds of social information and how much
they will pay to obtain it. As in our discussion of wanting and liking, Platt rightly assumed that rhesus
monkeys would value most what they like most, and that they would pay the highest price for what they
are most motivated to acquire.
Each monkey watched a slide show with viewing options akin to pay-per-view television. On a
given trial, they could watch one of two images for as long as they liked, each viewing option associated
with a particular amount of juice. For each pair of images, one delivered more juice than the other. Given
that these were thirsty monkeys , they should prefer more juice over less juice. If monkeys have no
interest in the images per se ⎯⎯ because they have no value ⎯⎯ then their viewing preferences should be
strictly determined by where they can get the most juice. If, on the other hand, the images have value,
and some images are more valuable than others, then they may be willing to look at an image that delivers
less juice over an image that delivers more. This is costly viewing. This is paying for watching.
Evidence for such preferences would reveal that rhesus monkeys value the social information that comes
from the image over the juice itself, a surprising result given that juice is a primary reward whereas the
image is only a secondary reward, indicative of things to come.
Consistently, these male monkeys had two favorite channels, preferring those showing pictures of
high ranking individuals and close-ups of female hindquarters. They preferred these over images of low
ranking individuals, despite the fact that this choice often cost them the opportunity to drink more juice.
Platt's findings show that monkeys are motivated to acquire information about socially relevant
situations, including information about dominance and sex. Their motivation or desire to obtain this
information is high, as evidenced by the fact that they are willing to pay a cost. Keeping an eye on a
dominant is of value as dominants pose a threat, especially one staring at you. Keeping an eye on a
female’s hindquarters is also of value as it can signal sexual receptivity: in rhesus monkeys, as in many
other monkeys and apes, the area around the vagina either swells, turns red, or both when females are
ovulating. This is important information for males in their attempts to court and mate females. I will
quickly pass over the potential implication of these results for thinking about the origins of pornography.
Humans also value social information, with many hours in a day devoted to obtaining such
information through gossip. Many of us live in a world where dominance matters, whether it is climbing
to the top of a corporate chain or attaining the title of heavyweight champion of the world. Individuals
seek high status because of the physical and health benefits that accrue. In such societies, our sense of
self is based on our comparison with others. It is also based on a strong sense of independence,
autonomy, assertiveness, and uniqueness. In other societies, the self dissolves into the other, with an
Hauser Chapter 2. Runaway desire 65
emphasis on inter-dependence, commonness, and openness to change in response to authority. These
differences in self-perception show up when we attend to faces of familiar individuals. Chinese subjects,
representative of a collectivistic and inter-dependent society, responded more quickly to seeing their
boss’s face than seeing their own face. In contrast, American subjects responded more quickly to their
own face than to any other person’s face, including that of their boss. Like Platt’s monkeys, therefore, we
too place value on social information. Unlike Platt’s monkeys, our sense of value in the social domain is
modulated by our cultural upbringing. This modulation, and the brain states that accompany it, shows up
in direct comparisons of individuals who are motivated to attain high dominance status with those who
are motivated to create equality.
The American social psychologist Joan Chiao used survey information to establish two groups of
individuals based on those who preferred to live in an egalitarian society and those who preferred a
hierarchical society. These individuals then entered a brain scanner and viewed pictures of people
experiencing pain. Two areas, both associated with the personal experience of pain and the perception of
pain in others, were highly active. But these areas were less active in those who preferred hierarchies
than those who preferred egalitarianism. This finding, as Chiao notes, is consistent with the idea that in
an egalitarian society, empathy for others well-being is essential. In egalitarian societies, seeing someone
who has less or is being harmed by another, should motivate a desire to redress the imbalance and reduce
the harm. In a dog-eat-dog hierarchical society, where dominants outcompete subordinates and inequities
are part of life, concern for those at the bottom is a sign of weakness. These results show how cultural
influences can shape brain activity, leading some to develop deep desires for dominance and inequities,
whereas others develop deep desires for equality. These brain areas heighten our sensitivity to what others
have, what we desire, and how our desires are modulated by what others have. These comparisons
motivate us to improve our status either by working harder ⎯⎯ a good thing ⎯⎯ or taking down those
above us ⎯⎯ a bad thing.
I’ll have what she’s having
One of the most famous lines in movie history was delivered by Estelle Reiner in When Harry Met Sally,
a comedy produced by her son Rob Reiner. While Estelle is seated at a table in a delicatessen, Sally ⎯⎯
played by Meg Ryan ⎯⎯ fakes having an orgasm to show Harry ⎯⎯ played by Billy Crystal ⎯⎯ that he
can’t tell the difference between fakes and the real deal. Overhearing Ryan’s performance, Estelle turns
to the waiter and says “I’ll have what she’s having.” This is comparative shopping, cashing in on
Hauser Chapter 2. Runaway desire 66
someone else’s subjective experience to guide our chosen experiences.
Orgasms and eating are two of the great pleasures in life, whether you live in Tokyo, Toronto,
Toulouse, Tehran or Timbuktu? I doubt any healthy human adult would debate this. What can be debated
is what counts as the ultimate orgasm or food experience. It can be debated both among friends and
inside our own minds, influenced by personal experience and our knowledge of what else is available, or
might be.
Consider potato chips. As a snack, potato chips generate a revenue in the United States of about
$6-7 billion dollars each year, relying on the slicing and frying of about 2 billion pounds of potatoes.
These facts make clear that most Americans love potato chips, and are motivated to consume them. Like
other salty snacks, it is hard to eat just one. The American psychologist Carey Morewedge and his
collaborators ran an experiment to find out how much people love potato chips, and whether their
anticipated fondness for this delicious crisp changes in the face of other options. Subjects sat at a table in
front of a bowl of potato chips and an alternative food that was visible, but out of reach. The alternative
was either a highly undesirable snack such as sardines, or a highly desirable one such as Godiva
chocolate. After subjects contemplated what it would be like to eat each of these foods, they then rated
how much they would enjoy them. This is like the study I described in the pleasure section where subjects
rated how much they would enjoy different vacation destinations, but without the comparison between
one clearly good and one clearly bad spot. Both focus on the anticipation of a pleasurable experience.
Subjects’ ratings of potato chip deliciousness soared when sardines were on offer, and plummeted
in the presence of chocolate. Context matters. What is clearly delicious when there is nothing else on the
table, loses or gains in deliciousness when the table fills up with other delectable or disgusting
alternatives.
What’s happening to our pleasure detector, and especially our anticipated reward system, in the
potato chip experiment? Are we incapable of understanding what makes us happy, unable to figure out
what is or is not delicious, or are we fickle? What Morewedge’s experiment reveals is that deliciousness,
like ugliness, stubbornness, and obsequiousness, is a judgment, judgments are always relative or
comparative, and as such, based on some standard that is either present in the moment, stored away in
our memories, or anticipated in the future. When Estelle Reiner uttered her famous line, she was using
Meg Ryan’s orgasmic expression of delight as a comparative metric. When we compare food items or
wine or pretty faces or sporty cars, we recruit our brain’s resources, especially the circuitry involved in
attention, emotion and memory. Whether we say that potato chips are the best snack, or better than
sardines, we have made a comparison that requires our attention, our capacity to keep at least two items in
memory, and a way of emotionally tagging each of the items. This comparison-shopping taxes our
mental resources, recruiting them away from the job of evaluating one snack, and leading to a distorted
Hauser Chapter 2. Runaway desire 67
evaluation of desirability.
Morewedge’s experiments point to a mismatch between how delicious something is and how
delicious we think it will be, or how delicious we thought it was. It reveals a distortion in our capacity to
anticipate ⎯⎯ or forecast in the words of the American social psychologist Daniel Gilbert ⎯⎯ how we will
feel, and in particular, how much we will like the experience. This is a problem for the elements of
pleasure that I laid out earlier in this chapter, as we expect the system that links wanting and liking to be
well honed, even optimized to make sure that we really want things we really like. Is this distortion
something to expect across the board, independently of context, or is it specific to our food? Is the social
domain similarly vulnerable to a distorted view of anticipated pleasure?
Consider revenge. When someone transgresses over the borders of social norms, either harming
us or those we care about, we often seek revenge, motivated to even things up. We often imagine that
revenge will make us feel better, providing a honey hit to the brain that will satisfy our desire to redress
an imbalance. But is this the outcome we consistently achieve when we follow through on a plot of
revenge or, as Sir Frances Bacon noted over three hundred years ago, might “A man that studieth revenge,
keeps his own wounds green, which otherwise would heal, and do well.” In more modern and plain
English, might our desire for revenge inoculate us against healing, creating an illusion that we will feel
better? If so, revenge looks like an addictive process, with wanting unhinged from liking.
The American psychologist Kevin Carlsmith set up an experimental game that allowed each
subject within a group to contribute money to a public good. At the end of one round, the bank multiplied
the total by a pre-determined amount, divided this total by the number of players, and then redistributed