In addition to dedicating years of his life to living among baboons in the African bush, Robert Sapolsky is a Stanford professor whose work sits at the nexus of primatology and neuroscience. Behave is a deep dive into the meaning behind human behavior. As his 800-page tome reveals, it’s a subject too complicated for any single field of science to explain adequately.

On one side of a street, there is a rooster. On the other side is a hen. The hen sends up every beguiling signal at her disposal to let the rooster know she’s ready to mate. The rooster is receptive, which raises the age-old question of why the chicken crossed the road.

Depending on whom you ask, the answer to the question will vary. The endocrinologist will talk about the hormones secreted in both hen and rooster that made the former irresistible to the latter. The bio-engineer would point to the skeletomuscular mechanics that made the rooster’s movement possible. The evolutionary biologist will talk about the mating rituals that evolved in birds over millions of years, ensuring survival. Each explanation begins and ends in the same basket.

For one thing, this is a painfully boring way of explaining behavior. For another, it’s incomplete. If we really want to understand the meaning behind a behavior, we need to think less in terms of the “best” scholarly basket to put all our eggs in, and more in terms of bands of context that surround a particular behavior. All the bands of context are connected and each has something important to tell us about what gave rise to a behavior. The size of these bands varies with time.

For example, we can look at what happens moments before an action, the band closest to the behavior (which involves looking at neural firings in the brain). We can ask what was happening hours or days before (which could involve investigating hormones secreted or environmental inputs that influence behavior). We could expand the circle to consider what habitual patterns of brain function developed over the course of the person’s life, or what experiences they had in early childhood or even in-utero. This pulls in genetics, family history, and cultural impact. You could widen the band of context even further, to encompass millions of years of evolutionary development that could have shaped the kinds of behavior seen over time.

Suddenly, we have a fuller picture of human behavior, supported by numerous interconnected fields of study that all contribute vital context and give meaning to the event.

This could all be a fancy way of saying, “It’s complicated.” It’s not a good idea to talk about human behavior from only one vantage point. Any vantage point has to connect to others. When we try to say that it’s all because of a particular neurotransmitter or gene sequence, we miss the forest for the trees.

The amygdala is a structure near the base of the brain that houses some of our most primitive reactions: aggression, fear, arousal, and anxiety. The amygdala is often exploding with neural activity in the seconds leading up to some of our more impulsive behaviors.

This small, almond-shaped structure generated some serious controversy back in the 1970s when surgeons performed operations that destroyed the amygdala in an attempt to dampen the aggressive impulses that a highly active amygdala promoted. The procedures were tragically imprecise and data about success rates is spotty at best. The practice has been mostly abandoned.

There are two notorious cases that shed light on the link between the amygdala and aggression. The first case involved a woman named Ulrike Meihhof. Meinhof had led a fairly pedestrian life as a journalist before being radicalized. She founded the terrorist group called the Red Army Faction in 1968, and was arrested for her involvement in bombings and robberies across West Germany. She hanged herself (or was she hanged?) in her jail cell in 1976, amidst the amygdala imbroglio. Her autopsy revealed a tumor butting up against her amygdala.

Another iconic case study was that of Charles Whitman. He was an Eagle Scout, a choirboy, a former marine, an off-the-charts brilliant engineer-to-be, married to a woman he dearly loved. But he’d been complaining to doctors about brutal headaches and violent urges. In 1966, he earned himself the now-famous moniker of “Texas Tower Sniper,” when he shot dead 16 people and wounded twice as many—after murdering his wife and mother. He left a surprisingly coherent suicide note by the bodies of his loved ones, declaring that he couldn’t say why he killed his wife, because he genuinely loved her “with all [his] heart.” He requested an autopsy on his brain and that all his money be donated to a health organization. As it turned out, Whitman was right. Like Meinhof in West Germany, Whitman had brain tumors touching his amygdala.

Such cases are not so simple as “tumor-tortured amygdala leads to violent murder.” It turned out that Whitman had a personal history of violence, just like his father. His brother was murdered in a bar fight. The history of violence was generational. Still, the amygdala is not a factor that can be ignored.

Oxytocin is a several-hundred-million-years-old neurotransmitter sometimes called the “cuddle drug” or the “love hormone” because of the way it promotes bonding between mates and between mother and child. There’s been a recent landslide of remarkable studies documenting just how powerful this hormone is and what it does.

A study of prairie voles (hang in there, this is actually interesting) found them to be monogamous. This is an anomaly for their genus. It turns out that the prairie voles’ brains secrete the same amount of oxytocin as other species, but their brains have far more of the necessary receptors, so they can take in more oxytocin, leading to stronger bonding.

The effects of oxytocin are tougher to study in human subjects, but higher levels of this neuropeptide have been linked to increased physical affection, synchronicity in movement and behavior, relationship longevity, and higher reported levels of  satisfaction among couples. When couples get a spritz of oxytocin via nasal spray, they tend to relate to each other in a more positive manner and stress hormone production drops.

In the last 50,000 years, evolution has hatched something unprecedented: bonding not just between mates or parents and children, but between species. Since the time that humans had domesticated wolves, oxytocin levels increased in both man and beast when they stared at one another. This doesn’t work with strangers, but only between owner and hound. The longer the gaze lingers, the more oxytocin is released. This is an extremely recent development, given that oxytocin has existed a thousand times longer than this new interspecies-bonding process.

Oxytocin also dampens the firing of the amygdala, taking us out of fight-flight-freeze. There was a Harvard study tracking Romanian orphans who had been adopted by families all over the world. A Romanian dictator in the late 1980s had banned birth control until after child number five. In the following years, thousands of unwanted children were left on the doorsteps of orphanages across the country. With the institutions overrun, most of these kids experienced extreme deprivation. In addition to low IQs, high rates of anxiety and depression, and difficulty trusting and attaching, researchers found below average brain size and connectivity in every region—barring the amygdalae, which were unusually swollen. These kids were tragically deprived in manifold fashion, and even adoption into loving, stable families couldn’t readily mitigate the swollen amygdala. What a difference oxytocin could have made in those Romanian children’s lives.

What oxytocin does is reduce fear and anxiety, and allows for the “all is calm, all is bright” parasympathetic nervous system to come online. Oxytocin delivers that almost-euphoric feeling of safety. When oxytocin levels are high, people are more trusting, and tend to see the best in others. They tend to interpret social cues more accurately, and view the actions and facial expressions of others more charitably.

If you dumped oxytocin in a city’s water supply, people would be more trusting, kind, and friendly. They would likely parent more empathetically. They would also fall for every piece of click bait and salesmanship that told them they needed this or that item or experience. Oxytocin can make us trusting to a fault. A cynical interpretation would be that too much oxytocin would make us suckers and pawns in the wily schemes of others. A more generous interpretation would be that oxytocin helps us turn the other cheek.

We are a tremendously violent species, but contrary to common belief, we don’t actually hate violence—what we hate is the wrong kinds of violence. The act of pulling on someone’s arm could be an act of heroism if it means pulling someone off the street and out of the way of a car; or it could be a horrible crime if someone is trying to pull you into a van against your will. The decision to pull a trigger could be heroic or heinous depending on whether it’s pulled to create a massacre or stop a massacre.

Context is everything. Violence has its place. The right kind of violence is awarded and celebrated, whether it’s a brave soldier returning from battle or a champion fighter in the ring. Women want to mate with those who are best at it. The wrong kind earns scorn and imprisonment. Context makes all the difference.

There’s another way in which humans are weird when it comes to violence. Like our other primate relatives, we have been known to knock each other’s brains out with blunt instruments from time to time. But there are many other times where our violence is not so straightforward. It’s done through court orders, clever social maneuvering that ostracizes a person or a group, or by looking the other way when there’s violence carried out against a rival.

Yet another puzzle about our violence is that we humans, so capable of violence, are also capable of remarkable sacrifice and goodwill. We’re becoming more altruistic, codifying it in our institutions. Very recently, our species has developed programs to adopt orphans from other parts of the world or to transfer money to areas struck by natural disasters; we’ve created peace forces and human rights watch groups; we’ve made treaties that ban chemical weapons and nuclear tests.

When we think of the Swedish people, we don’t think of bloodthirsty killers, but that was precisely their reputation only a few centuries ago. The contrast of Swedish history with today’s nature-loving, equality-conscious Swedes is striking. This transformation took place over just a few generations.

Change can take place over the course of a lifetime. John Newton was the captain of a slave ship and then an investor in the slave industry for years. But something remarkable happened. In an unbelievable reversal, he renounced the slave trade as evil, repented of his involvement therein, and began working with abolitionists to eliminate slavery in England. Newton’s radical change led him to pen the famous hymn “Amazing Grace.”

Change can take place in just days. During the First World War, soldiers fighting in France reached a truce that allowed them to come out of the trenches on Christmas Day. Originally, it was an opportunity for armies to bury their dead, but before long, opposing armies were helping each other carry and bury the dead. They prayed together. They had Christmas dinner together, exchanged gifts. By the next day they were playing soccer together. Some even exchanged addresses in hopes of contacting one another after the war. This lasted until the superiors from both armies returned and threatened their troops with death if they didn’t stop singing and playing and start shooting again.

Change can happen over the course of seconds. In one infamous moment in the Vietnam War, known as the My Lai Massacre, American troops raided an undefended village, killing children and the elderly and raping women. Almost 500 civilians were slaughtered. It only took one person to curtail the bloodshed. An American pilot named Hugh Thompson surveying the scene from above saw what was happening, landed his chopper between the Americans and the surviving villagers, trained his chain gun on his fellow soldiers, and told them he’d cut them all down unless they desisted. In mere seconds, the pilot undid all the us-them conditioning that had been embedded in his brain’s circuitry through the US military. This pilot, Hugh Thompson, wasn’t equipped with any special neurons or hormones. He was made of the same “stuff” as anyone else.

These stories illustrate the profound changes that take place in the brain that allow for radical reversals and bring out the best in us. The hackneyed warning that those who fail to learn from history are doomed to repeat it is only part of the picture. It’s also true that those who don’t study moments of tremendous human improvement will inevitably fail to repeat similar moments of human behavior at its best.