Empathy – the ability to feel or understand another’s emotions – is deeply rooted in our evolutionary past. Consider a simple example: a researcher pretends to cry in front of a family dog. The pet, unable to distinguish the fake sobs from real distress, whines and nuzzles the “upset” person, just as worried as a small child in the same situation. Such reactions hint that empathy isn’t unique to humans; it spans across species and likely evolved long before modern society.

From an evolutionary perspective, empathy conferred a survival advantage. Mammalian mothers who were attuned to their offspring’s needs were more successful in raising surviving young. Over 180 million years of mammalian evolution, natural selection favored parents (especially mothers) who responded to their babies’ cries and smiles – ensuring the young were fed, protected, and comforted. This “parental empathy” laid the groundwork for more complex social emotions. In humans, even infants show rudimentary empathy: newborns cry in response to other babies’ cries, as if emotionally echoing their peers. Such responses are automatic and hard-wired, suggesting empathy is not just a cultural trait we learn, but an innate capacity we refine.

Biologically, empathy is intertwined with the brain’s mirroring systems. In the 1990s, scientists at the University of Parma made a striking discovery in monkeys. Certain neurons in the monkey’s brain fired both when the monkey grabbed an object and when it watched another monkey perform the same action. These were dubbed mirror neurons, famously described as “monkey see, monkey do” cells. In humans, too, these neural mirror systems help us “feel” what others feel. If you see someone get pricked by a needle, for instance, regions of your brain involved in pain can light up in sympathy – a neural echo of the other’s experience. This automatic resonance forms the basis of emotional empathy: we literally experience a faint copy of what others are going through.

Empathy isn’t an all-or-nothing phenomenon; it ranges from basic to advanced forms. At its most elementary, empathy is simply emotional contagion – one animal’s distress spreading to another. But in more advanced forms, it includes perspective-taking and targeted helping. Remarkably, many animals show empathy-like behaviors. Rodents will share the fear of their companions – for example, a rat becomes anxious if it hears another rat squeal in alarm (Rats Show Empathy, Too | National Institutes of Health (NIH)) (Rats Show Empathy, Too | National Institutes of Health (NIH)). In a 2011 study, scientists placed rats in a situation where one rat was trapped in a tube while its companion was free. After a few sessions, the free rats learned how to unlock the tube to free their cagemates. They would consistently work to liberate a trapped friend, even ignoring a stash of chocolate chips to do so (Rats Show Empathy, Too | National Institutes of Health (NIH)). The rats showed prosocial behavior, apparently driven by empathy – they freed their peers even when there was no reward in it for them except relieving the other’s distress.

(The Evolution of Empathy | Greater Good) A mother chimpanzee reaches out to help her whimpering son down from a tree, responding to his cries for help. Empathy in our primate cousins often appears as consoling or helping behaviors, much like in humans.

Our primate relatives provide some of the most heartwarming examples of cross-individual empathy. In one classic observation from 1964, researchers found that rhesus monkeys refused to pull a chain to get food when they realized doing so shocked a companion. One monkey was so upset by witnessing another receive a shock that it didn’t eat for 12 days rather than cause further harm. Such self-starvation to protect a peer is a profound act of empathy – the monkey valued its companion’s wellbeing over its own immediate reward. Chimpanzees and bonobos, our closest genetic relatives, also display empathic concern. A famous account by primatologist Frans de Waal describes a bonobo named Kuni who found an injured starling in her zoo enclosure. Kuni gently picked up the bird and, after climbing the highest tree, carefully unfolded its wings and lofted it into the air, attempting to help it fly away to safety. When the bird didn’t make it out of the enclosure, Kuni stood guard over it, protectively, until it recovered. Chimpanzees, too, console distressed companions with hugs and pats, much as a human might comfort a friend. In one touching anecdote, a captive chimp named Joni stubbornly refused to come down from a high perch – until his caregiver feigned crying. Seeing his human friend “upset,” Joni rushed over, face filled with concern, gently touching the person’s face as if to understand the problem. Moments like these suggest that animals are capable of both feeling another’s pain and taking steps to soothe it.

Evolution seems to recycle and repurpose useful traits, and empathy is no exception. The basic emotional responsiveness that likely evolved for infant care was extended to other relationships – between mates, friends, and even across species. As social animals, being attuned to others’ feelings helps coordinate group activities and maintain harmony. In early human hunter-gatherer bands, an empathic individual who noticed a tribe-mate’s injury or hunger and helped address it would strengthen social bonds and mutual support, enhancing the group’s survival. Thus, empathy became a social glue, fostering cooperation. A lioness that senses another lioness gearing up for a hunt will join in, improving their success. A human who perceives a colleague’s stress might offer assistance, improving group productivity. In short, empathy allows creatures to work together and care for each other, which often benefits everyone involved. It is a biological legacy that underlies kindness, compassion, and the intricate social networks we see in many animal societies – especially our own.

Aggression: A Double-Edged Sword

If empathy is the glue of social life, aggression is the stark opposite – a force of conflict and competition. From snarling wolves tussling over a fresh kill to rival stags locking antlers in autumn duels, aggression is widespread in nature. But why would evolution favor such violent behavior? The answer lies in survival and natural selection. Aggression can be a strategy to secure vital resources – food, territory, mates – or to defend against threats. Creatures that could effectively intimidate or fend off rivals often had better access to resources and a higher chance to pass on their genes (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). Early humans, for instance, might have had to fight off predators or compete with other groups for hunting grounds. In those contexts, the willingness to confront and the capacity for aggression could mean the difference between life and death, or between reproductive success and failure. In evolutionary terms, traits that helped our ancestors survive or reproduce – including a capacity for aggression when needed – tended to be preserved and passed down.

However, aggression is very much a double-edged sword. While it can confer advantages, it also carries steep risks. Fighting can lead to injury or expulsion, so animals (humans included) typically don’t attack indiscriminately. It’s often a calculated behavior used when the stakes are high or when the odds of winning are in one’s favor (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). Natural selection doesn’t favor mindless violence; it favors advantageous violence. A bird defending its nest will attack a predator fiercely – because the cost of not fighting (losing offspring) outweighs the risk. But that same bird won’t gratuitously attack a stronger rival without cause, because getting injured could be fatal. In many species, rituals and displays evolved to minimize unnecessary bloodshed. Two stags roaring and strutting might settle who’s stronger before clashing horns. Likewise, early human tribes likely had posturing and displays of strength to avert constant lethal battles. In short, animals (and people) tend to use aggression selectively, when it promises more benefit than harm (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). Most of the time, alternative strategies like retreating or submitting keep the peace – an equilibrium that benefits survival.

Biologically, aggression is orchestrated by a primal duet between the brain and hormones. Deep in the brain’s emotional core lies the amygdala, an almond-shaped region that acts like an alarm system. The amygdala constantly scans for threats and, when it perceives danger or provocation, can trigger aggressive impulses (the classic “fight” side of the fight-or-flight response) (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). Imagine someone rudely shoves you – your amygdala flares, preparing you to shove back or defend yourself. But whether you actually attack depends on another brain region: the prefrontal cortex (PFC). The PFC, located right behind the forehead, is like the brain’s impulse control center, capable of inhibiting aggressive urges. If the amygdala is the gas pedal, the prefrontal cortex is the brake. Research has found that violent criminals often have reduced activity in their frontal lobes, suggesting their impulse-control brakes are weak. In extreme cases, damage to the PFC can turn even a mild-mannered person prone to sudden aggression because the usual checks on the amygdala’s fury are lifted. Thus, the neural circuitry of aggression involves a balance: emotional triggers from deeper brain areas, regulated (in well-adjusted individuals) by higher reasoning areas that weigh consequences and social norms.

Hormones add another layer to this story. The hormone testosterone, often dubbed the “male” hormone, has long been associated with aggressive behavior. In many animal species, males have far higher testosterone levels and also tend to be more aggressive, especially in competitions for mates or territory. Experiments have shown that increasing testosterone can increase aggression in animals like rodents and birds. In humans, the link is more complex but still present: higher testosterone is correlated with higher propensity for aggression in both men and women (9.2 The Biological and Emotional Causes of Aggression – Principles of Social Psychology – 1st International H5P Edition) (9.2 The Biological and Emotional Causes of Aggression – Principles of Social Psychology – 1st International H5P Edition). One illustrative study measured testosterone in a group of male college fraternity members. Fraternities with the highest average testosterone levels had reputations for wild, rambunctious antics and more physical conflicts on campus. In contrast, fraternities with lower testosterone profiles were known as friendly, studious, and cooperative (9.2 The Biological and Emotional Causes of Aggression – Principles of Social Psychology – 1st International H5P Edition) (9.2 The Biological and Emotional Causes of Aggression – Principles of Social Psychology – 1st International H5P Edition). Similarly, studies of prisoners found that inmates with higher testosterone were more likely to have committed violent crimes and violated prison rules (9.2 The Biological and Emotional Causes of Aggression – Principles of Social Psychology – 1st International H5P Edition). It’s important to note that testosterone doesn’t cause aggression out of nowhere – rather, it seems to prime individuals to be more sensitive to dominance challenges and less fearful of conflict. The effect goes both ways too: aggressive or competitive experiences (like winning a fight or even a sports match) can drive up testosterone temporarily.

On the flip side, a brain chemical that tamps down aggression is serotonin. Serotonin is a neurotransmitter associated with mood and impulse control. High levels of serotonin generally have a calming effect, while low levels remove some of the restraints on aggression. Studies have found that violent criminals often have unusually low serotonin activity. In laboratory experiments, boosting serotonin can literally make individuals less aggressive. In one study, volunteers were given a drug that increases serotonin and then engaged in a competitive game where they could “zap” an opponent with unpleasant noise. Those with boosted serotonin were far less aggressive in retaliating than those on a placebo. This suggests that serotonin helps the brain rein in impulses that might lead to explosive or uncontrolled aggression. The delicate dance between these chemicals – testosterone pushing toward aggression, serotonin holding it back – partly determines how aggressive an individual may be. Of course, countless other factors (stress hormones like cortisol, genetics, etc.) are in play, but testosterone and serotonin are two well-studied players in the biology of aggression.

Aggression doesn’t look the same in every species, or even in every situation. Context is key. Biologists often distinguish between proactive aggression (planned, goal-oriented aggression, like a predator stalking prey or a person hiring a hitman) and reactive aggression (hot-blooded, impulsive anger in the moment). Intriguingly, humans show a unique blend of these two types. Compared to other primates, we humans are relatively low on reactive, impulsive aggression – we don’t fly into violent rages as often as, say, chimpanzees do. Chimpanzees, especially males, can be notoriously quick to anger and attack within their group. Bonobos, on the other hand, are much less reactive; they diffuse tension with social bonding and are often called the “make love, not war” apes. Humans turned out to be more bonobo-like in our ability to inhibit raw anger – perhaps a result of our need for cooperative social living – yet we share with chimpanzees a high capacity for planned, calculated aggression (like organized warfare) (Two types of aggression in human evolution - PMC ). In our evolutionary history, being strategically aggressive (for example, planning a dawn raid on a rival clan) could yield big payoffs, whereas being hair-trigger temperamental was riskier in stable communities. This may explain why humans self-domesticated over time to be generally less reactive, more controlled – though certainly still capable of violence when it serves a purpose.

Different species also have different styles of aggression shaped by their ecology and social structure. In many mammal species, males are more physically aggressive than females – a pattern rooted in sexual selection. Because females often invest more in offspring (pregnancy, nursing, etc.), males compete for access to those limited opportunities to reproduce. The result is often evolution favoring larger size or greater aggression in males (think of stag deer fighting with antlers, or elephant seal bulls battling on a beach). Females, in contrast, might fight in defensive contexts (such as protecting their young) but less for mating rights. In humans, this pattern persists to a degree: statistics show men are more likely to engage in physical violence, while women’s aggression, when it occurs, more often takes non-physical forms (like social exclusion or verbal aggression). Of course, there is plenty of overlap, and cultural norms strongly shape how aggression is expressed by different genders, but the general trend aligns with our biological heritage seen across many animals.

Human aggression is highly modulated by culture and learning. What might be considered an appropriate aggressive response in one culture could be seen as abhorrent in another. One famous cross-cultural study examined the so-called “culture of honor” in the southern United States. In this experiment, researchers deliberately insulted young men to see how they’d react. A participant would be bumped by an actor in a hallway and called an “asshole” – a minor provocation. The results were striking: men from the U.S. South responded with a much sharper spike in stress and anger. Their testosterone levels surged, and they were more likely to respond aggressively or dominantly, compared to men from the North who were raised in a different cultural milieu. The interpretation was that Southern culture traditionally places a high value on personal honor and toughness – historically, in herding societies or lawless frontiers, a reputation for retaliation was a deterrent against theft or attack. Insults in such a culture demand aggressive redress, whereas Northern participants (with a culture less tied to honor reputation) were more likely to shrug it off. This is a vivid example of how cultural norms can amplify or dampen aggressive impulses. Similarly, some cultures socialize children from early on to control aggression and find non-violent conflict resolution, while others may reward displays of dominance and fighting spirit. For instance, certain Indigenous Arctic communities famously used humor and games to defuse conflicts rather than direct aggression, effectively teaching youth that anger should be met with ridicule, not violence. On the other hand, a child raised in a violent neighborhood or a gang culture might learn that striking back hard is the only way to survive or earn respect. These learned behaviors can override or enhance our innate tendencies.

In summary, aggression in humans and other animals is a complex interplay of biology and context. It evolved because it sometimes paid off in evolutionary terms, but it’s kept in check by both internal mechanisms (brains, hormones) and external pressures (social norms, laws, potential retaliation). Understanding aggression as an evolved trait helps explain why it can be so difficult to eradicate – it’s part of our natural toolkit – but also highlights why it varies so much between individuals and societies. It’s a tool that can be used or not used, shaped heavily by environment and experience.

Evolutionary Psychology: Our Past, Present, and Behavior

Evolutionary psychology offers a lens to view empathy and aggression as two sides of the same coin: strategies that helped our ancestors navigate a world of social cooperation and conflict. This field starts from a simple premise: the human mind, like the human body, is a product of evolution. Just as our lungs evolved to breathe air and our eyes to see, our emotions and social behaviors evolved to handle challenges in the ancestral environment. Empathy and aggression are seen not as random quirks of personality, but as adaptive features – mental tools shaped by natural selection because they solved problems in our evolutionary past.

How might natural selection have molded these behaviors? Think back to early human bands living tens of thousands of years ago. Empathy would have been invaluable in a cooperative group – it fosters bonding, altruism, and reciprocal helping. A tribe where members cared about each other’s wellbeing likely out-survived a tribe of selfish individuals, because those with empathy would share food with the hungry, tend to the sick, and support each other in hunting and defense. In evolutionary terms, altruism can be favored if directed toward kin (kin selection) or if it’s repaid in kind later (reciprocal altruism). The warm glow we feel when helping someone in need is possibly evolution’s way of rewarding behavior that, in the long run, benefited our gene pool. On the flip side, aggression would have been crucial in other scenarios: defending the group from rival tribes or predators, establishing one’s status and deterring exploitation, and competing for mates or resources when necessary (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). Individuals who completely lacked aggressive capacity might have been too passive to protect themselves or their offspring, whereas those who could aggress under the right conditions could secure vital resources.

Evolutionary psychology also emphasizes that these behaviors are context-dependent. Our brains have evolved to be flexible, adjusting our behavior to the situation at hand. This flexibility is evident in the way environment and genetics interact. We may have genetic predispositions (say, a temperament that is more prone to anger or more prone to empathy), but how life unfolds can enhance or suppress those tendencies. A well-known example is the so-called “warrior gene,” which refers to a variant of the gene MAO-A that affects neurotransmitters like serotonin. Research by Avshalom Caspi and colleagues found that men with a low-activity MAO-A gene variant were more likely to exhibit antisocial, aggressive behavior but only if they had been severely mistreated or abused in childhood (The Biological and Emotional Causes of Aggression | Principles of Social Psychology) (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). In people with loving, stable upbringings, that same gene variant did not lead to heightened aggression (The Biological and Emotional Causes of Aggression | Principles of Social Psychology) (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). This is a powerful demonstration of a gene-environment interplay: an aggressive outcome emerged from the combination of an evolutionary genetic predisposition and a harsh environment. Evolution likely equipped us with these genetic differences as a way to hedge bets – some individuals are born more sensitive to environments. If they grow up in a rough, competitive setting, their aggression-related genes might switch on to help them survive; if they grow up in a gentle, cooperative setting, those genes stay quieter, and empathy and pro-social behavior carry the day.

Moreover, evolutionary psychology sheds light on why we tend to be kinder to those who are closer to us genetically or socially. The theory of kin selection predicts that we are naturally inclined to protect and empathize with our relatives because they carry many of the same genes. Studies confirm this bias: for example, biological parents are far less likely to abuse or kill their children than stepparents are (The Biological and Emotional Causes of Aggression | Principles of Social Psychology). This disturbing statistic (sometimes called the “Cinderella effect”) is thought to reflect an unconscious evolutionary bias – adults invest more care and restraint in those who share their genes. Of course, human morality and culture can extend our empathy well beyond kin – we often treat friends, strangers, and even pets with kindness that has nothing to do with genetic relatedness. But evolutionary psychology suggests that this broad circle of empathy grew out of a core of family-first compassion in our deep past.

Natural selection also shaped psychological traits via trade-offs. Too much aggression could splinter a community or lead to deadly feuds – not good for long-term survival – so humans evolved nuanced social emotions like guilt, shame, and empathy to keep our violent impulses in check when living in close-knit groups. Conversely, too much empathy (or empathy indiscriminately applied to outsiders) in a perilous environment might have made early humans vulnerable to rival groups. Thus, our minds evolved to navigate a balance: cooperative and caring within our community, but wary and, if needed, aggressive toward threats. This might explain the stark contrast we see in human nature: the capacity for profound kindness and equally profound cruelty. In evolutionary terms, both sides were useful in different contexts.

It’s important to remember that “evolved” does not mean immutable or morally justified. Understanding the evolutionary roots of empathy and aggression doesn’t excuse violent behavior, nor does it diminish the value of compassion. Rather, it helps us see why these tendencies exist at all. Our Stone Age brains sometimes misfire in the modern world – a quick temper that was useful on the prehistoric savannah may be problematic on a crowded city street, for example. Recognizing this can help us find ways to channel our instincts productively. We can cultivate empathy through education and positive social norms, effectively “tuning up” that natural capacity. We can also create structures and laws that discourage harmful aggression, acknowledging that while the impulse may be natural, so is our ability to control it, thanks to our big prefrontal cortex and our deeply social nature.

In conclusion, empathy and aggression are two pivotal threads in the tapestry of human behavior, each with deep evolutionary origins. Empathy binds families and communities, stemming from the nurturing of offspring and flourishing in cooperative groups. Aggression, born from the harsh realities of competition and defense, ensured our ancestors could fight for survival when push came to shove. Evolutionary psychology weaves these threads together, showing how our brains were shaped to deploy either tenderness or fury as situations demanded. It’s a compelling reminder that much of what feels deeply human – our kindness and our conflict – is, in fact, deeply animal as well, forged in the crucible of evolution. Yet, knowing this history empowers us. By understanding the roots of empathy and aggression, we can better foster the former and manage the latter, aiming to live in a modern world that acknowledges our ancient impulses but isn’t ruled by them.