Explaining our taste for excessive harm
Marc D. Hauser
Viking/Penguin
For Jacques and Bert Hauser,
my parents,
my friends,
and my reminder
that life should be
lived to its fullest
Hauser Evilicious. Front matter 2
Pleasure is the greatest incentive to evil.
⎯⎯ Plato
To witness suffering does one good, to inflict it even more so.
⎯⎯ Friedrich Nietzsche
Man produces evil as a bee produces honey.
⎯⎯ William Golding
Hauser Evilicious. Front matter 3
Dear reader,
Having lived in Uganda and spoken with people who escaped from the savagery of the brutal
dictators Milton Obote and Idi Amin, having heard stories of my father’s childhood as a Jew running
through Nazi occupied France, and reading past and present-day accounts of genocide, I am familiar with
the horrors of evil. I have also been a student of human nature, trained as a scientist. These experiences
have propelled me to study the causes of evil, attempt to make some progress in explaining it to myself,
and hopefully to you. There is a great urgency to understanding this problem. None of us can afford to
passively watch millions of individuals lose their homes, children, and lives as a result of malice. Sloth is
a sin, especially when we live in a world where cultures of evil can so easily erupt.
I am also familiar with and deeply moved by human kindness, our capacity to reach out and help
strangers. When my father was in a boarding school in the south of France, hiding from the Nazis, a little
girl approached him and asked if he was Jewish. My father, conditioned by his parents to deny his
background, said no. The girl, sensing doubt, said “Well, if you are Jewish, you should know that the
director of the school is handing Jewish children over to the Nazis.” My father promptly called his parents
who picked him up, moved him to another village and school, and survived to tell the story. This little girl
expressed one of our species’ signature capacities: the ability to show compassion for another person,
even if their beliefs and desires are different.
In preparation for writing this book, I read transcripts and descriptions of thousands of horrific
events, listened to personal stories of survivors from financial ruin and war, worked with abused children
who were crucified by unfit parents, and watched both fictional films and documentaries that portrayed
psychopaths, dictators of totalitarian regimes, and their hapless victims. As one often does in these
circumstances, I developed a tougher skin over time. But I have never lost track of the human travesties
that result from evil. As my father’s story suggests, I have also not lost sight of the fact that we are a
species that has done great good, and will continue to do so in the future. Nonetheless, to provide a sound
and satisfying explanation of evil we must avoid falling into more romantic interpretations of the human
condition. Our best protection is science. This is the position I will defend.
The topic of evil is massive. This is, however, a short book, written without exhaustive
references, in-depth descriptions of our atrocities, and comprehensive engagement with the many theories
on offer to explain evil. What I offer is my own explanation of evil, of how it evolved, how it develops
within individuals, and how it affects the lives of millions of innocent victims. It is a minimalist
explanation of evil that is anchored in the sciences. I believe, as do many scientists, that deep
understanding of exceptionally complicated phenomena requires staking out a piece of theoretical real
estate with only a few properties, putting to the side many interesting, but potentially distracting details.
This book extracts the core of evil, the part that generates all the variation that our history has catalogued,
and that our future holds.
Sincerely,
Hauser Evilicious. Front matter 4
Acknowledgements
I wrote this book while my cat, Humphrey Bogart, sat on my desk, staring at the computer monitor.
Though he purred a lot, and was good value when I needed a break, he didn’t provide a single insight.
Nor did our other pets: a dog, rabbit, and two other cats. For insights, critical comments on my writing,
comfort, and endless love and inspiration, there is only one mammal, deliciously wonderful, and without
an evil bone in her body ⎯⎯ my wife, Lilan.
Marc Aidinoff … a Harvard undergraduate who joined me early on in this journey, digging up
references, collecting data, arguing interpretations, sharing my enthusiasm, while offering his own.
Kim Beeman and Fritz Tsao … my two oldest and closest friends. They have some of the richest
minds around. Their knowledge of film, literature and the arts is unsurpassed. Their capacity to bring
these riches to the sciences is a gift.
Noam Chomsky… for inspiration, fearless attacks on power mongering, and friendship.
Errol Morris… for heated discussion, camaraderie, and insights into evil through his
cinematographic lens and critical mind.
Many colleagues, students, and friends provided invaluable feedback on various parts of the
book, or its entirety: Kim Beeman, Kent Berridge, George Cadwalader, Donal Cahill, Noam Chomsky,
Jim Churchill, Randy Cohen, Daniel Dennett, Jonathan Figdor, Nick Haslam, Omar Sultan Haque, Lilan
Hauser, Bryce Huebner, Ann Jon, Gordon Kraft-Todd, Errol Morris, Philip Pettit, Steven Pinker, Lisa
Pytka, Richard Sosis, Fritz Tsao, Jack Van Honk, and Richard Wrangham.
My agent, John Brockman…not only a great agent but a wonderful human being who supported
me during challenging times.
My editors at Viking/Penguin, Wendy Wolff and Kevin Doughten. Tough when needed.
Supportive when needed. A unique blend. The book is all the better for it.
Hauser Evilicious. Front matter 5
Table of Contents
Prologue. Evilution
Chapter 1. Nature’s secrets
Chapter 2. Runaway desire
Chapter 3. Ravages of denial
Chapter 4. Wicked in waiting
Epilogue. Evilightenment
Hauser Evilicious. Front matter 6
Prologue:
Evilution
“There is no such thing as eradicating evil [because] the deepest essence of
human nature consists of instinctual impulses which are of an elementary
nature… and which aim at the satisfaction of certain primal needs.”
-- Sigmund Freud
I was drowning. This was not the first time. It was also not because I was a poor swimmer. I was 14
years old. A boy named Lionel James, who was the same age but twice my size, was shoving my head
under water, roaring with laughter as I struggled to gasp some air.
I usually managed to avoid Lionel in the pool, but sometimes he got the best of me while I was
playing with friends. Lionel wasn’t the only one who bullied me in junior high school. He was part of an
evil three pack, including Ronnie Paxton and Chris Joffe, each much larger and stronger than I. Almost
daily they locked me inside of the school’s lockers, bruised my arms by giving me knuckle-punches, and
gave me purple-nurples by twisting my nipples. This was no fun for me. For James, Paxton, and Joffe it
was delicious enjoyment. Sometimes, while I was locked in my locker, my math teacher would let me
out and then ask “Why do you get yourself into these situations?” Though I had great respect for my
teacher’s math abilities, and actually had a crush on her, she was socially daft. Did she think I asked to be
packaged up in the locker by my tormenters? It was sheer humiliation.
One day my mother noticed the bruises. Horrified, she asked what happened. I reluctantly told her
the story. She said we were going to talk with the principal. I told her I would prefer water drip torture.
She understood and we never went to see the principal.
The person who rescued me from my misery was my father, a man who had lived through the war
as a child, running from village to village to escape the Nazis, and in so doing, confronted thuggish farm
boys whose weight far exceeded their IQ. My father, upon hearing that I didn’t want to go to school
anymore, offered a compromise: he would pick me up for lunch every day if I kept going to classes. I
agreed, relishing the idea of escaping the lunch-time scene at school where James, Paxton and Joffe
pummeled me at will without getting caught.
Hauser Prologue. Evilution 7
A month passed. I felt better. My father told me that it was time to go back to lunch at school, but
with a plan, one centered around the notion of respect. The only way to command it from my tormenters
was to fight back. “But Dad,” I said, “if I hit them, they will crush me.” “They might,” he said, “but you
will have gained some respect, and they may turn their attention to someone else.” It seemed like a
remarkably stupid idea. But my father lived through a war and fought his way to respect among the thugs
in every village school. I decided to give it a go.
I went back to school. Soon thereafter, I found myself standing behind Paxton who displayed
biceps bigger than my head. I figured I had only one shot. I tapped him on the shoulder and swung as
hard as I could, hitting him square in the chest. What aim. What perfection. What wasted energy. With no
more than a flinch, Paxton looked down at me, fury in his face, and grunted “What’s up with you?” With
tears running and lips trembling, I sputtered “I can’t take it anymore. You, Joffe, and James are constantly
hitting me and locking me in the lockers. I can’t take it!” And then, as if his entire brain had been rewired,
serotonin surging to provide self-control, dopamine flowing to shift his sense of reward, the hulk spoke:
“Really? Okay, we’ll stop.” And just like that, Paxton, Joffe and James stopped. No more locker games,
no more bruises. They even saw me as a useful resource, someone who could help them pass some of
their exams. From victim to victory.
I was fortunate. Many are not. Thousands of children throughout the world are persecuted in a
similar way but never fight back or if they do, are crushed for trying. Some are pushed so hard that they
commit suicide, tragedies that increasingly make headline news reports.
The fact that bullies often torment their victims for personal gain, cause great harm, and often
enjoy the experience ⎯⎯ as did Lionel James ⎯⎯ fits well with a common view of evil. On this view, we
think of someone as evil if they inflict harm on innocent others, knowing that they are violating moral or
legal norms, and relishing the abuse delivered. But what of bullies who, due to immaturity or brain
deficits, simply don’t understand the scope of moral boundaries? What if they impose great harm on their
victims, but don’t enjoy the experience? What if the victims are not entirely innocent, such as those who
double-time as bullies?
We can debate questions like these on philosophical grounds, attempting to refine what, precisely,
counts as an act of evildoing as opposed to some mere moral wrong, like breaking a promise or having an
affair while married. Many have. I don’t believe, however, that this is how we will achieve our deepest
understanding. Instead, I turn to the sciences of human nature, focusing on cases where people directly or
indirectly cause excessive harm to innocent others as the essence of evil. To explain this form of evil, we
must dissect the underlying psychology, the brain circuits that generate this psychology, the genes that
build brains, and the evolutionary history that has sculpted the genetic ensemble that makes us
distinctively human. This is the approach I pursue. If I’m right about this approach, not only will we gain
Hauser Prologue. Evilution 8
a deeper understanding of how and why our species has engaged in evildoing, but we will learn about our
own individual vulnerability to follow suit. This prologue provides a sampling of the central ideas minus
the rich evidence and explanations that follow in the four core chapters of this book.
A brief history of malice
Homo sapiens, the knowing and wise animal, has logged an uncontested record of atrocities,
despite moral norms prohibiting such actions: no other species has abducted innocent children into rogue
armies and then killed those who refused to kill, tossed infants into the air as targets for shooting practice,
gang raped women to force them to carry the enemy’s fetus to term while destroying the souls of their
powerless husbands, and mutilated and burned men to death because more humane forms of killing were
less effective and enjoyable. These are horrific acts. They abound globally and across the ages. Many
scholars have judged them as evil.
Despite the pervasiveness of these atrocities, evil is commonly perceived as a defect, an
unfortunate malignancy that has engulfed and metastasized within our species’ essential goodness. Evil is
also denied, relegated to mythology, the delusional imagination of a few madmen, the propaganda of
imperialist nations, or the result of a rare mutation. Perhaps because of these impressions, we have an
obsessive fascination with evil, evidenced by our fertile capacity to create and then consume films about
genocide, cunning rapists, master criminals, corporate raiders, psychopaths and serial killers. We are of
two minds, wanting to hide from the atrocities of evil while feeding our insatiable appetite for more.
To understand evil is neither to justify nor excuse it, reflexively converting inhumane acts into
mere accidents of our biology or the unfortunate consequences of bad environments. To understand evil is
to open a door into its essence, to clarify its causes. In some cases, understanding may force us to
exonerate the perpetrators, recognizing that they harbored significant brain damage and as a result, lacked
self-control or awareness of others’ pain. In other cases, understanding will reveal that they knowingly
caused harm to innocent others, relishing the devastation left behind. By describing and understanding an
individual’s character with the tools of science, we are more likely to make appropriate assignments of
responsibility, blame, punishment, and future risk to society.
To understand evil requires facing our species’ sustained record of atrocities, laying out a variety
of cases for inspection. Former Reverend Lawrence Murphy was responsible for over two hundred
instances of sexual abuse, luring innocent deaf children in with a saintly smile. Charles Manson, the
illegitimate son of a sixteen year old woman and the self-proclaimed father of dozens of runaway women,
was responsible for the brutal death of five people by means of 114 knife jabs, while also prostituting his
Hauser Prologue. Evilution 9
lovers, beating his wife, selling drugs, and stealing cars. Former Chairman of the NASDAQ stock
exchange, Bernard Madoff, was responsible for initiating a Ponzi scheme involving money laundering,
perjury, and mail fraud that caused thousands of people to suffer financial ruin. Jane Toppan, born
Honora Kelley, was an American nurse who was responsible for killing over 30 patients by drug
overdose, stating in her testimony that she experienced a sexual thrill when she held dying patients, and
that her goal in life was to kill more innocent people than anyone else in history. Former military
specialist Charles Granger was responsible for forcing nudity and sex among the Iraqi prisoners of Abu
Ghraib, putting individuals on dog leashes, depriving them of their senses with head bags, and piling
naked bodies into photographed still lifes, orchestrations that led to the ultimate humiliation and
dehumanization of these prisoners.
Depending upon how we think about the problem of evil, we might consider the individuals noted
above as minor evildoers or not evil at all because the harms were rather insignificant, because their goal
wasn’t to directly harm anyone and then enjoy the trail of damage, or because they lacked the mental
capacity to assume responsibility for the atrocities committed. These individuals pale in comparison with
the most unambiguously radical evildoers of the 20-21 st century ⎯⎯ the dictators Idi Amin, Francisco
Franco, Adolf Hitler, Kim Jong-il, Slobodan Milosevic, Pol Pot, Josef Stalin, Charles Taylor, and Mao
Zedong. These men were responsible for the brutal deaths of approximately 80 million people combined.
Most were mentally healthy, at least in terms of clinical diagnoses. Many relished their atrocities. All
devised over-the-top means of ending lives. Whether by enticing or coercing their followers to torture,
gang rape, and butcher human flesh, they went beyond what was necessary to get rid of unwanted others.
These are excessive harms, carried out with excessive techniques. In this book, I will not only explore
these extreme cases, but more mundane ones as well. Each case helps shape our understanding of what
propells some individuals to cause harm on small or large scales, while others avoid it entirely, despite
temptations to the contrary.
Why and How?
To explain the landscape of human atrocities, from Reverend Lawrence Murphy to Mao Zedong, we need
an account of why we evolved this capacity and how it works. I will explain both of these problems using
the theories and evidence of science.
Why? Evil evolved as an incidental consequence of our unique form of intelligence. All animals
show highly specialized abilities to solve problems linked to survival. Honey bees perform dances to tell
others about the precise location of nutritious pollen, providing an information highway that lowers the
Hauser Prologue. Evilution 10
costs of individual foraging challenges. Meerkats teach their young how to hunt dangerous but energyrich
scorpion prey, providing an education that bypasses the risks of trial and error learning. Humans
unconsciously wrinkle their noses and pull back their lips into an expression of disgust that communicates
information about disease-ridden and toxic substances, thereby lowering the costs of sickness to others
who might be exposed. Each of these specializations involve exquisitely designed neural circuits and
sensory machinery. Each specialization is used for one and only one problem ⎯⎯ except in humans.
Animal thoughts and emotions are like monogamous relationships, myopically and faithfully focused on a
single problem for life. Human thoughts and emotions are like promiscuous relationships, broad-minded
and liberated, free to couple as new problems surface.
Unlike any other animal, the thoughts and emotions we use to solve problems in one domain can
readily be combined and recombined with thoughts and emotions from other domains. This is powerful,
providing great flexibility in addressing novel problems, some of which we create for ourselves. Disgust
provides an example. Disgust originally evolved as an adaptive response to detecting substances that are
toxic to our health, especially substances that are outside of the body but should be inside: feces, urine,
blood, and vomit. Within the circulation of a promiscuous brain, however, disgust journeys to distant
problems, including the moral attitude of vegetarians toward meat eaters, our revulsion toward incest, and
abhorrence of gratuitous torture. This journey involves the same brain mechanism that serves original
disgust, together with new connections that give voice to our moral sense. Promiscuity enables creativity.
What the sciences reveal is that the capacity for promiscuous thinking was realized by
evolutionary changes in the number of newly wired up brain areas. By increasing these connections, it
was possible, for the first time, to step outside the more narrow and specialized functions of each
particular brain area to solve a broader range of problems. Though we don’t know precisely when these
changes occurred, we know they occurred after our split from the other great apes ⎯⎯ the orangutans,
gorillas, bonobos and chimpanzees. We know this from looking at both the brains of these species, as
well as the ways in which they use tools, communicate, cooperate, and attack each other. Not only are
there fewer connections between different regions of the brain, but their thinking in various domains is
highly monogamous, faithfully dedicated to specific adaptive problems.
Empowered by our new, massively connected and promiscuous brain, we alone migrated into and
inhabited virtually every known environment on earth and some beyond, inventing abstract mathematical
concepts, conceiving grammatically structured languages, and creating glorious civilizations rich in
rituals, laws, and beliefs in the supernatural. Our promiscuous brain also provided us with the engine for
evil, but only as an incidental consequence of other adaptive capacities, including those that evolved to
harm others for the purpose of surviving and reproducing.
Hauser Prologue. Evilution 11
All social animals fight to gain resources, using highly ritualized behaviors to assess their
opponents and minimize the personal costs of injury. Changes in hormone levels and brain activity
motivate and reward the winners, and minimize the costs to the losers. In a small corner of the landscape
of aggressive fighting styles are an elite group of killers, animals that go beyond harming their opponents
to obliterating them: ants, wolves, lions, and chimpanzees. When these species attack to kill, they
typically target adult members of neighboring groups, using collaborative alliances to take out lone or
otherwise vulnerable victims. The rarity and limited scope of this form of lethal aggression is indicative
of monogamous thinking, and tells us something important about the economics ⎯⎯ especially the costs
and potential rewards of eliminating the enemy, as opposed to merely injuring them. Killing another adult
is costly because it involves intense, prolonged combat with another individual who is fighting back. The
risks of significant personal injury are therefore high, even if the potential benefit is death to an opponent.
As the British anthropologist Richard Wrangham has suggested, animals can surmount these costs by
attacking and killing only when there is a significant imbalance of power. This imbalance minimizes the
costs to the killers and maximizes the odds of a successful kill. Still, the rarity of killing reinforces an
uncontested conclusion among biologists: all animals would rather fight and injure their opponents than
fight and obliterate them, assuming that obliteration is costly to the attacker. In some cases, we are just
like these other animals ⎯⎯ killophobic.
Historical records, vividly summarized by Lieutenant Colonel Dave Grossman in his book On
Killing, reveal that in some situations, soldiers avoid killing the enemy even though they could have. For
example, despite the fact that Civil War regiments had the potential to kill 500-1000 individuals per
minute, the actual rate was only 1-2 per minute. This suggests that under some conditions, killing another
when you can see the whites of their eyes is hard. But as the history of genocides reveal, we have
evolved ways to bypass this limitation, making us killophilic in a variety of situations. Our brain’s unique
capacity for denial is one of the liberating factors.
By recruiting denial into our psychology’s artillery, we invented new ways of perceiving the
enemy or creating one, distorting reality in the service of feeding a desire for personal gain. Denial, like
so many aspects of our psychology, generates beneficial and toxic consequences. Self-deceiving
ourselves into believing that we are better than we are is a positive illusion that often has beneficial
consequences for our mental and physical health, and for our capacity to win in competition. Denying
others their moral worth by reclassifying them as threats to our survival or as non-human objects is toxic
thinking. When we deny others their moral worth, the thought of killing them is no longer aversive or
inappropriate. If we end someone’s life in defense of our own, we are following our evolved capacity for
survival. When we destroy a parasite, we are also protecting our self-interests to survive. And when we
destroy an inanimate object or lock it away, there is no emotional baggage because we have bypassed the
Hauser Prologue. Evilution 12
connection to individual rights; we have cut out morality as the governor. This suite of transformations,
enabled by our promiscuous brain, allowed us to occupy a unique position within the animal kingdom as
large scale killers.
Chimpanzees only kill adults when there are many attackers against one victim, with the vast
majority of kills focused on individuals outside of their own group; most kills within the group are aimed
at infants, where the costs to the attacker are low. Though humans also kill members of enemy groups
when there are many against one ⎯⎯ a pattern that is common among hunter-gatherers and other smallscale
societies ⎯⎯ we depart from this narrow pattern in terms of numbers and the array of potential
victims. When humans kill, we go at it with many against many, one against one, and even one against
many, including as victims both those outside of our group and those within, young and old, same and
opposite sex, and mating partner and competitor.
Add the chimpanzee’s adaptive capacity for coalitionary killing to the promiscuous capacity of
the human brain, and we arrive at a uniquely aggressive species, one capable of inflicting great harm on
others in any context. Though the modern invention of scud missiles and stealth bombers undoubtedly
enriched our capacity to kill on a large scale by putting distance between killers and victims, these
weapons of mass destruction were not necessary. Today, we need only travel back a few years to 1994 to
witness the machete genocides of Rwanda, a painful memory of our capacity to wipe out close to a
million people in 100 days with hand to hand combat. This is excessive harm, enabled by our ability to
use denial to minimize the perceived costs of killing another person and to motivate the anticipated
benefits. Denial turns down the heat of killing another and turns us into callous predators.
Evolutionary changes in the connections to the brain’s reward system provided a second, costoffsetting
step, allowing us to move into novel arenas for harming others. When an animal wins a fight,
the reward circuitry engages, providing a physiological pat on the back and encouragement for the next
round. This same circuitry even engages in anticipation of a battle or when watching winners. The
reward system is important as it motivates competitive action in situations that are costly. There is one
situation, however, where the reward system is remarkably quiet, at least in all social animals except our
own: detecting and punishing those who attempt to cheat and free-ride on others’ good will.
Punishment carries clear costs, either paid up front in terms of resources expended on physically
or psychologically attacking another, or paid at the end if the victim fights back or retaliates. These costs
can be offset if punishers and their group benefit by removing cheaters or teaching them a lesson. Among
animals, punishment is infrequently seen in vertebrates, especially our closest relatives the nonhuman
primates. When it is seen, the most common context is competition, not cooperation. Like lethal killing,
then, punishment in animals tends to be restricted to a narrow context. Like lethal killing, punishment in
animals is psychologically monogamous.
Hauser Prologue. Evilution 13
Punishment in humans is emblematically promiscuous. We castigate others whenever they
violate a social norm, in both competitive and cooperative situations, targeting kin and non-kin.
Punishment is doled out by the individual directly harmed and also by third party onlookers. We use both
physical and non-physical means to discipline cheaters, including ostracism. Punishment’s landscape is
vast.
The idea I develop here, building on the work of scholars in economics, psychology, and
anthropology, is that our species alone circumvented the costs of punishment as an incidental
consequence of promiscuity, including an intimate coupling between the systems of aggression and
reward. As several brain imaging studies reveal, when we either anticipate or actually punish another, or
even witness punishment as a mere bystander, our reward circuitry delivers a honey hit. Delivering just
deserts, or watching them delivered, is like eating dessert. We absorb the costs of punishment by feeling
good about ratting out the scourges, banishing them from society, and sometimes from life itself.
Ironically, as the economist Samuel Bowles has suggested based on mathematical models and a synthesis
of the historical record, punishment can strengthen solidarity and cooperation within the group, while
simultaneously enhancing antagonism and prejudice toward those outside the inner sanctum. Ironically,
the psychology that benefited cooperation among like-minded others may also have functioned to destroy
those who have different beliefs and values.
The emergence of promiscuous punishment was a momentous event in human history, a
celebration of exquisite brain evolution and adaptive design. But this achievement carried a hidden cost, a
debt that we continue to pay: A mind capable of feeling good about punishing in the name of virtue is a
mind capable of doing bad to feel good. It is a mind that finds real or simulated violence entertaining and
seeks ways to satisfy this interest. It is a mind that enjoys watching others suffer while singing O
Schadenfreude. It is a mind that is capable of feeling good about killing others who are perceived as
parasitic on society. It is a mind that can override the anticipated costs of killing by fueling a taste for
killing.
Desire, denial, aggression and reward are each associated with specific psychological processes,
distinct evolutionary histories, and specific adaptive problems. When processed by a promiscuous brain,
these systems connect in ways that are both beneficial to human welfare and deeply deleterious.
How? Evil occurs when individuals and societies allow desire for personal gain to combine with
the denial of others’ moral worth to justify the use of excessive harms. Everyone has desires, resources
they want and experiences they seek. Our desires motivate us into action, often to fulfill personal needs or
to help others. We all desire good health, fulfilling relationships, and knowledge to explain the world.
Some also desire great wealth and power, each culture weighing in on its signature vision of what counts:
money, land, livestock, wives, and subordinates. The desire system motivates action in the service of
Hauser Prologue. Evilution 14
rewarding experiences. Some actions have benign or even beneficial consequences for the welfare of
others, while others have malignant and costly consequences.
Exquisite studies pioneered by the American cognitive neuroscientist Kent Berridge have
uncovered the core elements of pleasure, including distinctive systems of wanting, liking and learning.
We, and hundreds of other species, often want things we like, and like things we want. This is, obviously,
an adaptive coupling. Thanks to experiments at the level of genes, neurons, and behavior, we can tease
apart these three systems. Thanks to naturally occurring situations, we can watch these systems come
unglued over the course of addictions, leading to the paradoxical and maladaptive situation of wanting
more and more, but liking the experience less and less. Addictions, as archetypal examples of excess,
provide a model for thinking about evil and its trademark signature of excessive harm.
The paradoxical decoupling between wanting and liking is seen most clearly in studies of obesity
in rats and humans, where individuals develop skyrocketing desires for food, but fail to experience
comparable pleasure from eating. By definition, those who become obese are prone to eat in excess. One
reason they do is because eating, or even seeing images of food, no longer delivers the same honey hit to
the brain as in their pre-obesity days. The reward system turns off when we turn to excess. This is
adaptive because nothing in excess is good. But because the wanting system runs independently, the
adaptive response by the liking system has the unfortunate consequence of making us want more even
though we enjoy it less. The proposal I develop in this book is that the same process is involved in evil,
especially its expression of excessive harm. It is a process that is aided by denial.
Everyone engages in denial, negating certain aspects of reality in order to manage painful
experiences or put forward a more powerful image. But like desire, denial has both beneficial and costly
consequences for self and others. When we listen to the news and hear of human rights violations across
the globe, we often hide our heads in the sand, plug our ears, and carry on with our lives as if all is okay
on planet Earth. When doctors have to engage in slicing into human flesh to perform surgery, they turn
off their compassion for humanity, treating the body as a mechanical device, at least until the surgery is
over, and the patient awakes, speaks and smiles. When we confront a challenging opponent in an athletic
competition or military confrontation, we often pump ourselves up, tricking our psychology into believing
that we are better than we are. Denial turns down the heat of emotion, allowing a cooler approach to
decision making and action. But doctors in denial concerning the moral worth of others can be convinced
to carry out heinous operations for the “good” of science or the purity of their group, and military leaders
in denial of an opponent’s strength can lead their soldiers to annihilation. Individuals in denial can reject
different aspects of reality in the service of reward, whether it is personal gain, avoiding pain, or enabling
the infliction of pain on others.
Hauser Prologue. Evilution 15
In a competitive world with limited resources, our desire system never rests. This is a good thing
as it motivates us to take care of our self-interests and strive for bigger and better. But a desire system
that never sleeps is a system that is motivated to accrue ever larger coffers or power. To satisfy this
inflationary need is often not possible without harming others, either directly or indirectly. To offset the
costs of harming another, desire recruits denial. This is a recipe for evil and the creation of excessive
harms. It is a recipe that takes two, often benign and highly adaptive ingredients that are essential for
motivating action and promoting survival, and combines them into an explosive outcome. Seen in this
way, our capacity for evil is as great as our capacity for love and compassion. Evil is part of human
nature, a capacity that can’t be denied. What I will show is both how this capacity works, and how some
of us, due to biological inheritance and environmental influence, are more likely to end up as evildoers.
Historical material on the lives of Franz Stangl and Adolf Eichmann, leaders in the Nazi
annihilation of Jews, illustrates how desire and denial combine within individual minds to create
excessive harms. Although this is a historical example, focused on the lives of only two men, stories like
theirs have been recounted hundreds of times, all over the globe and across time. This pattern points to
common mechanisms, identified in detail by the sciences of human nature.
Stangl was a politically motivated man with a burning desire to climb to the top of the Nazi
hierarchy. A clear path opened when he was appointed commander of the Polish prison Treblinka.
Unbeknownst to Stangl, Treblinka was one of the Nazi’s concentration death camps. To fulfill his desire
for power therefore required harming thousands of others, or more accurately, commanding Nazi soldiers
to harm others on his behalf. But since Stangl had no burning desire to harm the Jews, he dehumanized
them, transforming living, breathing, feeling, and thinking people into lifeless “cargo” ⎯⎯ his own
expression. Stangl was dry-eyed as officers under his command killed close to one million Jews, one
third of them children. The reward? Power and status within the Nazi hierarchy. The death of innocent
Jews was a foreseen consequence of Stangl’s desire for power, not his direct goal.
Eichmann, Lieutenant Colonel in the Nazi regime, was considered one of the central architects of
the Final Solution, the master plan for the extermination of Jews. Eichmann denied Jews their humanity
by championing the pamphlets and posters that portrayed them as vermin and parasites. This
dehumanizing transformation empowered Eichmann’s belief that cleansing was the only solution to
German integrity and power. Eichmann’s reward? Elimination of the Jews. Unlike Stangl, killing Jews
was rewarding. As the historian Yaacov Lozowick stated “Eichmann and his ilk did not come to murder
Jews by accident or in a fit of absent-mindedness, nor by blindly obeying orders or by being small cogs in
a big machine. They worked hard, thought hard, took the lead over many years. They were the alpinists of
evil.”
Hauser Prologue. Evilution 16
Stangl and Eichmann: two different routes into evil. Both possible and both equally lethal to
humanity.
This is a lean explanation of why evil evolved and how it develops within individuals and
societies. It is an explanation that strips evil down to its root causes, focusing on the core psychological
ingredients that enable us to violate moral norms and cause excessive harms to innocent others.
A difficult journey
This book takes you on a journey into evil. It is a story about our evolutionary past, our present state of
affairs, and the prospects for our future. It is as much a story about you and me, as it is about all of our
ancestors and future children. It is a story about the nature of moral decay and the prospects of moral
growth. It is story about society’s capacity to engineer great harm, and about our own individual
responsibility to avoid joining in.
Explaining how our genes create brains that create a psychology of desire and denial that leads to
excessive harms provides a satisfying explanation for the landscape of evil. It explains all varieties of evil
by showing how particular genetic combinations can create moral monsters and how particular
environmental conditions can convert good citizens into uncaring killers and extortionists. This
explanation will not allow us to banish evil from the world. Rather, it will enable us to understand why
some individuals acquire an addiction to feeling good by making others feel bad, and why others cause
unimaginable harm to innocent victims while flying the flag of virtue. This, in turn, will help us gain
greater awareness of our own vulnerabilities by monitoring the power of attraction between desire and
denial.
Hauser Prologue. Evilution 17
Endnotes: Prologue. Evilution
Recommended books:
There are numerous books about evil, most written by philosophers, theologians, historians, political
scientists, and legal scholars. The following recommendations are for books about evil written by
scientists. They are terrific, I have learned a great deal from them, and some of their ideas powerfully
enrich the pages between these covers.
Baumeister, R. F. (1999). Evil. Inside human violence and cruelty. New York, W.H. Freeman.
Baron-Cohen, S. (2011). The Science of Evil. New York, Basic Books.
Oakley, B. (2007). Mean Genes. New York, Prometheus Books.
Staub, E. (2010). Overcoming Evil. New York, Oxford University Press.
Stone, M. H. (2009). The Anatomy of Evil. New York, Prometheus Books.
Zimbardo, P. (2007). The Lucifer Effect. New York, Random House.
Notes:
• For a philosophical account of the nature of goodness that treats evil as a deviation from our species’
repertoire, see Philippa Foot Natural Goodness (2001, Oxford, Clarendon Press).
• For an explicit, philosophical argument for the connection between pleasure and evil, see Colin
McGinn‘s Ethics, Evil and Fiction (1997, Oxford, Oxford University Press). For a comprehensive
discussion of evil by a philosopher, including important critiques of the existing literature, see John
Kekes’ The Roots of Evil (2007, Ithaca, Cornell University Press)
• On killing throughout history: Wrangham, R.W. & Glowacki, L. (in press). Intergroup aggression in
chimpanzees and war in nomadic hunter-gatherers: evaluating the chimpanzee model. Human Nature;
Bowles, S. (2009). Did warfare among ancestral hunter-gatherers affect the evolution of human social
behaviors? Science, 324, 1293-1298; Choi, J.-K., & Bowles, S. (2007). The coevolution of parochial
altruism and war. Science, 318, 636-640; Grossman, D. (1995). On killing: the psychological costs of
learning to kill in war and society. New York, NY: Little, Brown.
• For a summary of research on desire, especially the elements of wanting, liking and learning, see
Berridge, K.C. (2009). Wanting and Liking: Observations from the Neuroscience and Psychology
Laboratory. Inquiry, 52(4), 378-398; Kringelbach, M.L., & Berridge, K.C. (2009). Towards a functional
neuroanatomy of pleasure and happiness. Trends Cognitive Science 13(1), 479-487.
• The most serious treatment of Stangl can be found in the penetrating interview by Gitta Sereny (1974,
Into that Darkness: From Mercy Killing to Mass Murder. London: Random House). There have been
different treatments of Adolf Eichmann, most famously by Hannah Arendt in her Eichmann in Jerusalem:
A report on the banality of evil. (1963, New York, Viking Press). Arendt’s perspective on Eichmann as
an ordinary gentleman who simply followed orders has been seriously challenged, suggesting that he was
anything but a banal evildoer; the quote by Holocaust scholar Yaacov Lozowick is one illustration of the
more generally accepted view that Eichmann was a radical evildoer with heinous intentions to
Hauser Prologue. Evilution 18
exterminate the Jews. He may have lived a calm and peaceful existence outside of his day job at Nazi
headquarters, but this was no ordinary citizen.
Quotes:
• Quote by Lozowick on Eichmann and banality of evil: Lozowick, Y. (2002) Hitler’s Bureaucrats: The
Nazi Security Police and the Banality of Evil. New York, Continuum Press, p. 279.
Hauser Prologue. Evilution 19
Chapter 1:
Nature’s secrets
Nature hides her secrets because of her essential loftiness, but not by means of ruse.
— Albert Einstein
In Charles Darwin’s day, biologists unearthed the mysteries of evolution by means of observation,
sometimes accompanied by a simple experiment. This was largely a process of documenting the patterns
of variation and uniformity that nature left behind. Only breeders were directly involved in manipulating
these patterns, using artificial selection to alter the size, shape, coloration, and lifespan of plants and
animals.
The Darwins of today continue this tradition, but with new tools, informed by understanding of
the genetic code and aided by technical developments in engineering, physics, chemistry, and computer
science. These tools allow for deeper penetration into the sources of change, and the causes of
evolutionary similarities and differences. They also enable biologists to change the course of evolution
and the patterns of development by turning genes off or turning novel ones on, and even creating
synthetic organisms in test tubes ⎯⎯ a wonderful playground for understanding both questions of origin,
change, and extinction.
The Darwins of today are cowboys, trailblazing a new frontier of understanding. But like the
frontier of the early American wild west, nature holds many secrets and surprises. Sometimes when we
break through nature’s guard, we gain fundamental truths about the living world, knowledge that can be
harnessed to improve animal and human welfare. But sometimes when we break through, we create toxic
consequences and ethical dilemmas. Tampering with nature is risky business as there are many hidden
and unforeseen consequences.
In 1999, the molecular biologist Joe Tsien and his team at Princeton University tampered with
mother nature. Their discovery, published in a distinguished scientific journal, soon filled the
newspapers, radio airwaves, and even a spot on Dave Letterman’s late night television show. Tsien
manipulated a gene that was known to influence memory, causing it to work over time. This created a
Hauser Chapter 1. Nature’s secrets 20
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 coauthor
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.
Hauser Chapter 1. Nature’s secrets 21
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
Hauser Chapter 1. Nature’s secrets 22
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
Hauser Chapter 1. Nature’s secrets 23
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
Hauser Chapter 1. Nature’s secrets 24
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
Hauser Chapter 1. Nature’s secrets 25
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 whitebearded,
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 parts as the parts, together with their interdependence,
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
Hauser Chapter 1. Nature’s secrets 26
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 Ampulex compressa tackles a specific species of cockroach, inserts a
first stinger into its body to cause leg paralysis and eliminate fighting, then a second
Hauser Chapter 1. Nature’s secrets 27
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.
•A 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 brainwashed
the caterpillar, hijacking its evolved instincts to care for its own young.
•A solitary wasp in the genus Sceliphron 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
Hauser Chapter 1. Nature’s secrets 28
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
Hauser Chapter 1. Nature’s secrets 29
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
Hauser Chapter 1. Nature’s secrets 30
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,
Hauser Chapter 1. Nature’s secrets 31
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-thanhuman
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
Hauser Chapter 1. Nature’s secrets 32
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,
Hauser Chapter 1. Nature’s secrets 33
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
Hauser Chapter 1. Nature’s secrets 34
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 followthrough?
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.
Hauser Chapter 1. Nature’s secrets 35
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
Hauser Chapter 1. Nature’s secrets 36
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 selfcontrol.
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.
Hauser Chapter 1. Nature’s secrets 37
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