Excerpted from Touching a Nerve: The Self as Brain, by Patricia S. Churchland. Copyright © 2013 Patricia S. Churchland. With permission of the publisher, W. W. Norton & Co., Inc.

The Joy of Hating
Sometimes play fighting crosses the line into real fighting. Sometimes defensive combat emerges when trust should prevail. Sometimes the wiring for impulse control is overwhelmed. By ideology. By rhetoric. By fear and hate. Sometimes . . . all hell breaks loose.

Fans of the San Diego Chargers football team are full of hate for fans of another California football team, the Oakland Raiders. They taunt each other, donning costumes to intimidate or humiliate the opposing team’s fans. Some of the fans engage in ritual fight displays, not unlike those of aggressive birds such as the Noisy Miner.

Chargers fans say the Raiders are evil, disgusting, and subhuman. And vice versa. Maybe it is just play hate. Evidently it is fun. All sides hugely enjoy the hate fest. Any casual observer can see that the fans derive enormous pleasure from belonging to a group that is united in its hate for the other group. The very hate itself seems to be exciting, invigorating, and pleasurable. Not incidentally, an astonishing amount of time and expense goes into this ritualistic hostility.

Nevertheless, in the United States, fighting between the fans at football games (U.S. football) is quite rare. On the exceptional occasion when it does occur, fans generally express horror and outrage. In England, however, one group of fans having it out with another group is not rare. Fighting among male fans after matches, and sometimes during and before matches, has been disturbingly popular among a subset of men. Football brawls happen routinely. Hooliganism has been exceptionally difficult to wipe out.

The BBC documentary on football fight clubs shows that for many young men, brawls between rival groups are terrifically exciting. Brawls are a major reason for attending matches, whether in the hometown or in France, Italy, or elsewhere in Europe. In the United Kingdom, the gangs are referred to as “firms.” Football firms are well organized, with a “top lad” who plays a leadership role and organizes fighting events around football matches.

What are the men of football firms like? To judge from the BBC documentary, they are charming, articulate, and bright. They were not beating their chests or frothing at the mouth. They did not look crazed. They could be your brother or cousin. The normality of their manner seems incompatible with their love of brawling, and yet it is not. This is essentially brawling without cause. It is brawling for the sheer fun of it.

The Los Angeles riots of 1992 erupted as racial and ethnic tension boiled over following the acquittal of three white policemen who had been videotaped viciously beating a black man, Rodney King. The outrage at the unfairness was profound, and suddenly all hell was unleashed: arson, looting, and shooting were occurring all over South Central Los Angeles.

I saw the video images of the hapless white trucker, Reginald Denny, forcibly yanked from his truck at an intersection by four black youths. They savagely kicked him and smashed his head with a brick, almost killing him. Watching the event on video again now, I cannot but be stunned, as reporters were at the time, by the joyous body language of the youths as Denny lay semiconscious on the ground. They danced with joy. Mostly unconcerned, people were milling all around the intersection. Fortunately, four black citizens, having seen the Denny beating on television, went to his rescue and took him to the hospital. But for their kind actions, he likely would have died.

Utter chaos reigned in the city for several days. The police had to back off because they were so deeply mistrusted and hated that they had become a popular target of gunfire. The National Guard had held back because their ammunition had not been delivered. Some Korean shopkeepers tried to defend their property by shooting looters, while others elected instead to simply watch as their shops were looted and burned.

Here, in the midst of the frustration and anger of the rioters and looters, there was joy and some sense of justified pleasure in striking back. One woman with a video camera reported, “When I was on the streets, people were having a ball. They were stealing and laughing and having a bunch of fun.” At least 54 people were killed, and thousands more were injured.

With absolutely no pretext save losing the Stanley Cup to the Boston Bruins in a fair hockey series, hockey fans in June 2011 went on a rampage in downtown Vancouver, burning cars, looting shops, and causing mayhem. Yes, this was Canada, where these things are not supposed to happen. In this instance, too, the joy of the fans, mostly young men, was unmistakable. They danced on overturned cars, smashed store windows, set fire to vehicles, and taunted the police, who struggled to maintain some semblance of order.

Cage fighting, I am told by my friend Jonathan Gottschall, is his passion. This seems peculiar to me, as he is a professor in a literature department. He tells me that the appeal of cage fighting is completely different from that enjoyed in riots and brawls. As Jonathan says, this is basically a friendly form of mutual assault. One-on-one, where the fight is fair, in the sense that officials match the pugilists in age, weight, and standing, is very different from mob brawls. Fear is the overriding emotion before the fight; intense attention is the main mental state during the fight. According to the cage fighters, the only pleasure comes at the end of the fight, and only if you win. The pleasure of defeating your opponent is so incredibly intense, it makes the risk worthwhile. Some cage fighters say it is a kind of ecstasy, comparable only to sex. This connection is less surprising than it first seems. Sexual behavior and violence are linked in the brain, in a region of the hypothalamus (ventral medial). In male mice, activation of some neurons in this tiny area provokes aggressive behavior to other males put in the cage, but provokes mating behavior when females enter the cage.

Hate gets classified as a negative emotion, and we might assume that negative emotions are the opposite of pleasurable. But in reflecting on the hate of sports fans or rival gangs, you cannot but notice that it tends to be energizing. Arousal is pleasurable. Sometimes it is called being “adrenalized.” So it is.

The comedian Louis C.K. describes standing in a long queue at the post office. He looks at other people in the line. He immediately sees things about them to hate. What idiotic shoes that guy wears; what a dumb question the customer is asking; what a loser. Contempt keeps him amused until his turn comes up. Despising others, however trivial the pretext, feels wonderful.

What else is going on in the hate state? You are familiar with guilty pleasures—doing on the sly something that is only modestly bad but still forbidden, like showing each other your bare childhood bums behind the barn, for example. What fun when you are 5. What a delicious secret to keep from your parents. In watching the videos of the Vancouver riots, the joy of breaking the rules, and doing so with others, was palpable.

Women are usually bystanders in hostility rituals and murderous raids. By and large, the perpetrators are men, and mostly, apart from a leader, they are young or middle-aged adults. A long-standing hypothesis is that the males of a gang are, in part, performing for each other. Their hostility displays reassure one another of their mutual attachment, their reliability in case of attack, and their common purpose. Their bonding gives them feelings of power, the power of numbers. That is linked to pleasure. Clothed alike in white sheets, rhythmically dancing around a huge bonfire, the men of the Ku Klux Klan appear to be having a ball. If duty alone were the incentive, no one would show up.

Females are not without aggression, however. Generally, but not always, it just takes a different form. Mean gossip, unkind cuts, shunning—all are potent forms of aggression used by females. Hair pulling seems to be making a comeback these days. Here as well, some form of pleasure seems to derive from collective hating. As with the football fans, there seems to be both intense ingroup bonding and intense hostility to those in a rival group or perhaps someone excluded from all groups.

Us versus them delineates the border of one’s safe group. Within the group, individuals can count on affection and adherence to group norms. Outside the group, interactions are riskier and individuals have to be more vigilant. The form that the hostile behavior takes toward those in the outgroup depends on what is in your toolbox, which depends in part on your genes and in part on what you pick up from your culture as the right way to do things. You model yourself after those you admire. Much simplified, in many cultures boys bash, girls shun.

When I was in ninth grade, a rather homely and forlorn girl with whom we had all been acquainted from the first grade began to be visibly pregnant. Being slow in class, she had generally been shunned as “retarded.” She failed to pass through the grades and struggled to learn to read. Dorothy was, so far as the girls in their tight cliques were concerned, essentially a nonentity. How had Dorothy become pregnant? She had no boyfriend, and in our village, everyone knew who was dating whom. As we all came quickly to know, one of the local lads, a logger, had taken her out and “had his way with her.” Beer was likely a factor. Did we feel sorry for her? Did we offer condolences for what was surely rape or the next thing to it? Were we dismayed by the lad’s taking advantage of a simpleminded girl?

Not a bit of it. We wallowed in our superiority, we basked in our wholesomeness and how grand it was that we were not Dorothy. We thought that her predicament was the sort of thing that happened to a girl like her; certainly not to girls like us. Such contempt was not an emotion generated when each of us was alone; then, individually, we were pretty scared by what had happened to Dorothy. Somewhat ignored before, Dorothy now was completely ostracized. Disgraceful though our behavior certainly was, the contempt quickly, and yes, joyfully, bubbled up when three or four of us assembled. Such scorn was part of what kept us so tightly bonded together. Hate binds, and social bonds are a joy.

At about the same time that we scorned Dorothy’s predicament, a chore befell me at the farm. Our white leghorn hens, generally a sociable crew, had ganged up on one miserable hen that had somehow acquired a scratch on her neck. The flock would not leave her alone. Swarming around her, the other hens pecked at any sight of blood, opening her wound further. They would have killed her, but my father told me to remove her and make a special pen to put her in until she healed. She still had a year or so of good laying, not yet old enough for the stew pot. Why, I asked, do hens behave in such a horrible way? “Well,” came the reply, “I don’t know. They just do.” The analogy with Dorothy was not lost on me. I regret to say, however, that it made not one whit of difference to my behavior.

Many years later, my friends and I looked back on the Dorothy episode with unequivocal self-loathing. Having matured, we assessed our adolescent behavior with something akin to disbelief. How had we allowed ourselves—even encouraged each other—to be so mean? Could we really have been like that then? Will our daughters be like that?

Wiring for Aggression
How does aggressive behavior serve animals, including us? Ultimately, aggression, in all its themes and variations, is about resources, sustaining life, and passing on one’s genes. No surprise there. So, used judiciously, aggressive behavior can often benefit an animal. For predators, aggression against prey brings food. For prey, aggression is defensive, along with fleeing and hiding. Thus, a wolverine is both intensely aggressive in the hunt, but also in protecting food and driving off intruders. Unlike voluntary cooperation in social animals, aggression is very ancient.

If you are engaged in predation or defense, you have to be “up” energetically. You cannot be in “rest-and-digest” mode. As neuroscientist Jaak Panksepp observed many years ago, energy is delight. Feeling energetic feels good. It feels exciting.

Consider predators, such as a wolf pack hunting elk. To be effective, the wolves’ motivation to kill must be strong, strong enough to overcome fear of a prey that can lethally kick and horn-gouge, but not so strong as to induce recklessness. A delicate balance. The wolves that keep to the rear of the elk try to rip the leg tendons without getting kicked. Those harassing from the front try to keep clear of the dangerous horns. They aim to rip out the throat. The wolves attack the beast and defend themselves at the same time.

This mix of energy, strong desire, fear, and vigilance is crucial for hunting success. Overpowering the prey means success, and success means food. And that, of course, means pleasure. Maybe the pleasure-hostility link is also, in part, owed to the response of the reward systems to a victory, with the result that on the next occasion, mere anticipation of victory brings pleasure. In other words, the animal gets a dopamine hit after the first prey catching. The brain then associates the predatory action with the pleasure of eating. That value is then attached on the next occasion to the goal itself. Anticipatory pleasure is real pleasure.  What are the neurochemicals at work in generating this pleasure? Endogenous opioids? Endocannabinoids? Dopamine? All of the above?

Defense against attackers, too, has its “up” feeling, though defense will also involve fear, possibly overwhelming the thrill of being energized for action. Endogenous opioids are probably released, enabling the animal to keep fighting back despite injury. This would partially explain the feelings of pleasure. It also explains the frequent phenomenon whereby only modest pain is felt during a fight, even when a person is shot or hit hard. Success in defense leaves us awash in joyful energy, any fear having utterly vanished. The pleasure of success in beating off a predator is empowering. I can do it! Failure? Defeat, especially chronic defeat, makes animals depressed and withdrawn.

Aggressive behavior can also emerge in defense of offspring. From the perspective of evolution, mammalian parents who respond with ferocity to threats to their offspring are likely to have more offspring survive than those who timorously abandon their offspring to an early death—other things being equal, of course. Hence, the genes of the ferocious defenders will spread; those of the timorous will not.

The determination of parents is breathtaking. Crows will mob and dive-bomb anyone who comes close to a newly fledged crow; a mother squirrel will hurl herself into the maw of a dog to give her baby a chance to escape. A mother bear, otherwise fairly shy, can be a powerhouse of fury if she perceives her cubs to be threatened. Protecting the young is a massively powerful impulse among mammals and birds. Human parents may be at their most aggressive in trying to get their child into Harvard or Stanford.

Predation and defense are forms of competition. The intended prey is competing against the predator for its life, the predator is competing against the intended prey for its protein. There is also territorial aggression, which is really a proxy for food. A patch of land will support only a limited number of animals, such as bears or barn owls. The bear who has command of that territory will roust others eager to partake of the berries on his turf. It is easy to see how territorial aggression would have been selected for, just as it is easy to see how predators of one kind or another inevitably emerged. Territoriality probably evolved many times, just as color vision and sociality evolved many times.

Could there have been a world without aggressive behavior? Probably not our world anyhow. Natural selection inevitably involves competition for resources. At some point in biological evolution, some creature will have the capacity to kill and eat others. Just as inevitably, some of those others will eventually be born with the capacity to resist, perhaps by camouflage, perhaps by beating a hasty retreat, making a terrible smell, or fighting back. The arms race is on.

Competing for the Best Mates
Then there is sex. In most mammalian and bird species, there is competition between males for access to females. Such competition can take many forms, but often it entails driving off or outperforming would-be suitors in hopes of impregnating a suitable female. In mating season, in full rut, a couple of bull moose, for example, will fight head-to-head until one finally tires or recognizes his weaker position and scuttles off. In a baboon troop, the alpha male has greater privileges with the troop females than do other males, and he will fight challengers to maintain his status. The lower-ranking males find ways of mating out of sight of the alpha male, sometimes involving significant deception.

Using a different strategy, male bowerbirds build fancy structures to attract females, and competing males will, on the sly, try to wreck them. And among blue Manakins, the males dance, each trying to outperform the other. Females select those perceived by them to have the most sophisticated dance—or so it seems to a human observer. The females select the male, and for these bird species, aggression is less important than performance, presumably because performance has come to signify what the female wants in a mate—virility and competence (a good brain).

Human mating behavior is more complicated. Like much human of behavior, it is subject to such a high degree of shaping by cultural norms and conventions, by fads and trends, that you can only marvel at the flexibility of the human brain. Sometimes human mating behavior seems to have borrowed something from the bowerbird, something from the head-butting moose, and something from the lekking of the sage grouse. In humans, as in most other mammalian species, males compete for females. There are displays, often conventionalized within the norms of a culture: displays of power, strength, wealth, beauty, generosity, cleverness, and social status. Depending on the culture, females may also compete with each other, and female selection may play a major role in mating.

Aggression is multidimensional. It has multiple triggers, variable mixes of emotions, and variable manifestations. It can serve any one of a set of diverse purposes. Within a species, there is apt to be considerable variability among individuals in the taste for aggressive behavior. Being slow to anger may serve animals better in times of peace and plenty, whereas a hot-tempered disposition may be more beneficial during times of scarcity or war. Moreover, an animal may be quick to respond in defense of the brood, but slower in preparation for an attack on prey.

Male and Female Brains
In our school, fighting was not allowed in the school yard, so the boys who wanted to fight marched over to the footbridge that crossed the irrigation flume, just over the edge of the school’s boundary. This was a good venue, as onlookers could seat themselves along the bridge rails and cheer on their favorite. These fights did not amount to much other than the odd bloody nose and a generous helping of crow. The teachers let it go unless the frequency was considered too high, whereupon the principal called in the likely suspects and gave them the strap. That kept the business in bounds. The girls did not fight. They gossiped. They could, of course, be spiteful and cruel, especially to other girls, but they did not actually engage in a slugfest. This tends to be the pattern worldwide, though of course local customs and biological variability allow for exceptions.

It is well known that human males more commonly engage in physical fights than females. The rates of convictions for assault, battery, and murder are vastly higher in men than in women. Men are typically the ones who hold up the stagecoach, rob the banks, go to war, and knife their way out of a bar fight. This is true pretty much everywhere. What explains this difference between males and females?

Testosterone is an essential element in the story, but the story is massively complex in very surprising and interesting ways, making offhand comments about testosterone poisoning in males a poor indication of the facts. Before outlining the role of testosterone in aggression, it may be useful first to briefly address how human male and female brains differ and the mechanisms whereby these differences are established and maintained.

Normally, when a sperm fertilizes an egg, the resulting human conceptus has 23 pairs of chromosomes. A pair of sex chromosomes is either XX (genetic female) or XY (genetic male). In the early stages of development, the sex organs (gonads) of the fetus are neutral, but during the second month of fetal development, genes on the Y chromosome produce proteins that transform the neutral gonads into male testes. Absent this action, the gonads grow into ovaries. In the second half of development, testosterone produced by the fetal testes is released into the bloodstream and enters the growing brain. Testosterone now comes to affect the anatomy of the male brain.

How do sex hormones interact with the growing fetal brain? The fast answer is that a surge of testosterone masculinizes the fetal brain by altering the number of neurons in very specific areas that mainly concern reproductive behavior, such as mounting and penetrating. In the absence of the testosterone surge, the brain follows a typical female path. So the female brain plan can be thought of as the default—it is what you get unless testosterone masculinizes the brain. As we shall see, however, even when testosterone is available, other factors, including timing of testosterone release and the amount released, may mean that the brain is not masculinized after all or it may be masculinized to some lesser degree.

What does it mean to say that the brain is masculinized? Testosterone affects the number of neurons forming a network. More exactly, it prevents the death of neurons in the affected network. Consequently, several neuronal groups (nuclei) in the hypothalamus are more than twice as large in males as in females.

Why is there any cell death in a developing brain? In general, the developmental blueprint for making nervous systems allows for production of excess neurons. Then the neurons are culled as a function of how effectively the neurons are working in their networks. This is a bit like hiring extra players at the beginning of the football season and then culling them down to make the best team. Testosterone affects the developing brain by downregulating the culling process—the cell death. So the size of a region will reflect the amount of culling undergone. The pattern is laid down in the fetal brain but is maintained throughout life, with an additional testosterone surge in puberty. The circuitry that was organized by hormones in fetal development is activated by hormones during puberty.

Small but important correction: Once it passes from the blood into the brain, some testosterone is transformed by an enzyme into a more potent androgen, dihydrotestosterone. And some of that is then changed into estradiol, which goes on to masculinize the brain. Paradoxical though it may seem, estradiol, a female hormone, is crucial for the masculinizing development. Biology is funny that way. It uses whatever works to get the job done.

So why doesn’t the female fetal brain get masculinized? After all, the fetal ovaries make estrogen aplenty. Owing to genes on her XX chromosomes, the female fetus produces a protein that soaks up and destroys much of the circulating estrogen produced by the ovaries. This operation can vary, depending on the genes and timing of gene expression. Puzzling as it may seem, moreover, low levels of estrogen feminize the brain, whereas high levels masculinize it. Progesterone in the brain also helps to feminize the hypothalamus.

Couldn’t I have left out that correction about estradiol? Possibly, but it conveys all by itself the fact that surprising mechanisms are in brains and bodies because we are evolved animals, not designed from scratch by a team of engineers. It also conveys a small irony. Ultimately, it is a female hormone that plays a big role in masculinizing the male brain.

Where do these testosterone-sensitive changes happen? Mostly in small regions of the hypothalamus, an evolutionarily ancient structure. Some hypothalamic nuclei regulate thirst and drinking behavior, others regulate hunger and eating behavior. As we saw in Chapter 4, some hypothalamic regions are important for parental care in mammals. Yet other regions regulate sexual behavior. These hypothalamic regions are important in the male’s sexual behavior—his interest in females and his capacity to mount and penetrate the female.

The size of these cell groups in the hypothalamus is not by itself the cause of male versus female differences in sexual behavior and sexual feelings. What really makes the difference is the pattern of connections among the neurons within each group and the connections between one group and other networks in the brain. The size is just one structural difference that we can currently detect. Because the size correlates with stereotypical male sexual behavior, that tells us what to study next to begin to uncover the broader causal details.

In a slightly different part of the hypothalamus—an area shown in rats to be important for ovulation—the neurochemical dopamine inhibits cell death. In the female brain, this area expands—not prenatally, however, but during puberty. In males, the cells in this area are not only fewer in number but also different biochemically, making and releasing homegrown opioids. If by chance a female had opioid neurons in this area, they would inhibit ovulation. The cells in this area project into the nearby pituitary gland, and this is the crucial communication channel between brain and ovaries. When these neurons are active, the pituitary releases hormones that stimulate the ovaries to produce estrogen. The female cycle of release of eggs from the ovaries will then begin.

Within the male (XY) and the female (XX) populations, there is individual variation in the number of neurons in the sex-sensitive hypothalamic nuclei; that is, some men will have about the same number of neurons as some women. Averages are only averages, not invariant principles.

Another significant difference between male and female brains may help explain why females are somewhat more fearful and cautious than males. This holds not just for humans, but for other mammals as well. And I mean, of course, on average. So some particular female hyena may be less fearful than some particular male hyena. In female brains, the hypothalamus (the ventral medial area) is more densely connected to another subcortical structure, the amygdala. The amygdala is important for generating the fear response and for learning what is to be feared. From an evolutionary point of view, the female mammal’s role in pregnancy, birth, and child rearing means that she is vastly more vulnerable than the males. She needs to be a little more cautious. To be sure, the behavioral significance of the amygdala difference is not yet thoroughly understood, and many environmental factors likely go into a particular person’s profile of risk aversion and fear. Nevertheless, the finding may well lead us to a fuller understanding of these average differences in behavior.

Intricate also are the interactions between a whole orchestra of potent neurochemicals that can affect mood, personality, and temperament. They can affect risk taking, aggression, trust; whether you are shy or outgoing, easygoing or prickly. Levels vary across individuals and also within a person over time. They include such neurochemicals as serotonin, vasopressin, oxytocin, stress hormones, and somatostatin. What else is in the orchestra? Well, there are interactions involving other parts of the body, including the pituitary gland, thyroid gland, and adrenal glands. And then there is the immune system, which interacts with all these things, and the brain.

Finally, the masculinizing of the gonads (making testes, penis, and prostate) occurs before the masculinizing of the brain. Owing to variability in the pathways controlled by genes and the interactions among the items in the suite of neurochemicals, sometimes the masculinizing of the brain does not follow the typical path and may be incomplete in various ways. You could have male genitalia and a female brain.

Rats have been the model animals used in figuring out the fundamentals of the gonad-brain story. But you are not just a big rat. So, is the human hypothalamus like the rat hypothalamus? Pretty much. The basic anatomical differences in hypothalamic structures of male and female lab rats are also seen in humans. Nevertheless, human sexual and social behavior is vastly more complex. Your very large brain, especially your huge prefrontal cortex, means that your flexibility in navigating your social world and your capacity to control sexual behavior is far more rich and varied and involves much more learning than in the case of a rat. In large-brained mammals, the interaction between gene expression and learning-based changes in the brain becomes a dense thicket of complexity.

This chapter is focused on aggression, and given the statistics on male aggression, that means we need to consider what makes a male brain male. But that is not enough. To understand the masculinization of the fetal brain at a deeper level, it is useful to see that nature does not always follow the beaten path. Reflecting on these other paths allows us a broader understanding of how hormones can affect our very nature. Then we shall return to the matter of male aggressive behavior.