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In our final episode of Crash Course Psychology, Hank discusses the ideas of Aggression and Altruism. These two things are difficult to understand and explain so sit tight and get ready to run the gauntlet of human emotions.

Want more videos about psychology? Check out our sister channel SciShow Psych at!

Introduction: Robber's Cave Experiment 00:00
Conflict vs. Cooperation 2:26
Aggression 3:05
Genetic, Neurological, & Biochemical Reasons for Aggression 3:26
Frustration-Aggression Hypothesis 4:24
Altruism 5:17
Bystander Effect 5:48
Why do we help others? 6:57
Social Exchange Theory & the Norm of Reciprocity 7:19
Social Responsibility Norm 7:47
Conflict & Self-Interest 8:09
Review & Credits 9:37

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CC Kids:
Hank Green: Let me tell you about Robber's Cave.  In 1954, a group of 11 boys, all about 12 years old, were invited to a special summer camp in the deep woods of Southeastern Oklahoma, at a place called Robber's Cave State Park.  None of the boys knew each other, although they all came from similar backgrounds.  They spent their days bonding over things like games and swimming and treasure hunts, and in no time, they formed a tight friendly group.  They even came up with a name for themselves: the Rattlers.  

But soon they began to notice something.  No, not a guy in the woods with a hockey mask, there was another group of boys also 11 of them, also the same age, that had been staying at the other end of the park the whole time.  The Rattlers never interacted with these other boys, so they didn't know that those kids were also spending time bonding over games and swimming and treasure hunts, and that they'd come up with a name for themselves, too: the Eagles.  But the Rattlers didn't like the look of the Eagles, oh, no, they didn't like them using their baseball diamond or their dining hall.  

And the feeling was mutual.  It didn't take long for each group to start complaining to the camp's counselors about the other gang, and eventually, they both said that they wanted to set up a contest to determine once and for all which group was better.  The counselors were only too happy to comply, because as I'm sure you've figured out by now, those counselors were actually researchers.  

The man who set up what would be remembered as the Robber's Cave Experiment was Turkish American social psychologist Muzafer Sherif.  He was interested in what it would take for rivals to overcome their differences and resolve their conflicts.  Specifically, Sherif wanted to test something called Realistic Conflict Theory.  He hypothesized that conflict happens when you combine negative prejudices with competition over resources, and the boys at Robber's Cave were well on their way to proving him right.  

Over the next couple of days, the Rattlers and the Eagles competed against each other for prizes in a series of games, like tug-of-war and foot races, and soon, what started as your basic trash talking and taunting and name-calling morphed into fist-fights, thefts, and raids on each others' cabins.  But then their dynamics changed or were changed for them.  

After the games were over, the researchers integrated the groups and gave the kids shared goals that they could only achieve through cooperation.  The tide quickly turned.  All 22 boys worked together to move a stalled truck that was carrying their food, they took care of a partially felled tree that was deemed a danger to the camp, they collaborated in setting up tents, even though they weren't given complete sets of equipment.  While isolation and competition made enemies of the strangers, shared goals and cooperation turned enemies into friends.  

Over the past 39 weeks, we've learned a lot about ourselves, our emotions and our personalities, how our minds can get sick, how we can help them get well again, why we can do vicious things and then turn around and act like heroes.  So maybe it's fitting that we wrap up this course by looking at a couple of opposing forces that some consider the very definition of human nature: aggression and altruism.  Conflict and cooperation.  You might think of it as the psychology of war and peace, or simply, what we can all learn from a bunch of 12 year olds.

(CrashCourse Psychology Intro plays)

In psychology, aggression is defined as 'behavior intended to hurt or destroy someone, something, or even yourself.'  People aggress, as psychologists say, in all kinds of ways, verbally, emotionally, and physically, and for lots of different reasons: out of anger, to assert dominance, or as a response to fear.  But that's just a glimpse into why someone might become aggressive.  Where does the aggression actually come from?

Like a lot of behaviors we've talked about it, it seems to emerge from that familiar combination of biological factors, like genetic, neurological, and biochemical influences, and our environment and experience.  In terms of genetic influences, studies of twins, and yes, CrashCourse Psychology might have been called CrashCourse Studies of Twins, showed that if one identical twin has a violent temper, often the other one does, too, but fraternal twins are much less likely to be so similar.  Neurologically speaking, no single area of the brain controls aggression, but certain areas like the limbic system do appear to facilitate it.  Research on violence and criminality has also revealed a link between aggression and diminished activity in the frontal lobes, which play a vital role in impulse control.  And finally, our aggressiveness can be influenced by our own biochemistry, hormones like testosterone and glucocorticoids and pheromones have all been implicated in animal models of aggression.  It's a little trickier in humans, it's a lot trickier in humans, but it's highly likely that our hormones are intimately linked with feeling and showing aggression.  

Obviously, aggression isn't just about biology.  Psychological and cultural factors also play an important role, as does the power of the situation.  For example, there's the Frustration-Aggression Hypothesis, the simple idea that people become aggressive when they're blocked from reaching a goal.  To demonstrate, consider the not-very aggressive sport of baseball.  There's a study that analyzed 44 years worth of baseball stats, and focused on the more than 27,000 incidents when a pitcher hit a batter with a ball.  It turned out that this was most likely to occur if the pitcher was frustrated by a recent home run or if one of his own teammates had been hit by a pitch in the previous inning.  

But we also learn aggression by watching others.  Like, if you grew up watching your parents throw popcorn and jeering lewdly at their most hated soccer team, you might have learned something from their behavior.  So combine all of those biological factors and funnel them through a particular person with a particular history in a particular situation, and you can begin to see how aggression can have many roots that grow together.

Thankfully, though, humans are more than their bad tempers.  While some things in people will leave us annoyed and angry, others breed friendship and affection.  So yes, there are positive topics in social psychology, like altruism, our selfless, even self-sacrificing regard for the welfare of others.  This could be something as simple as jumpstarting a stranger's car or as heroic as running into a burning building to save someone.  But if being altruistic is so awesome, why aren't we all that way all the time?  Or maybe the better question is, why do we ever do anything selfless, like, what's in it for us?

In the late 1960s, social psychologists Bibb Latane and John Darley conducted a series of experiments examining when and why we help others.  In one experiment, they placed a subject in a room, sometimes alone, sometimes with two other subjects, and sometimes with two actors posing as subjects.  Then, they simulated an emergency by filling the room with smoke and waited to see if the subject would do anything to alert the others or help themselves.  If the subject was alone, they'd report the smoke 75% of the time.  But subjects in a group of three only spoke up 38% of the time.  And when they were stuck in the room with two oblivious actors, only 10% of the participants said anything to the others.  Darley and Latane found that people typically helped others only if they noticed the incident, interpreted it as an emergency, and then finally, assumed responsibility, and all of these things were much more likely to occur if a person was alone, while the presence of others deterred the person from helping.

This kind of diffusion of responsibility referred to as the bystander effect, can weaken our instinct for altruism.  The bystander effect is a bit like the concept of social loafing that we talked about.  If you're around other people, it's easier to think that someone else is going to pick up the slack or in this case, come to the rescue.  

When people do decide to help others, they may do it for a number of reasons.  One perspective is that we tend to help others mainly out of self-interest.  By this thinking, helping really isn't altruistic at all, and instead, our actions boil down to a sort of cost-benefit analysis.  Like, maybe we'd turn in a lost wallet because we're hoping for a reward or we pitch in on a project at work because we think we'll get recognized and promoted by our bosses.  Social psychologists contextualize these kinds of examples in the broader theory of social exchange.  When it comes to doing things for other people, we're always trying to maximize our personal rewards while minimizing our personal costs.  But social exchange doesn't have to be as selfish as that, it can also mean that we act altruistically because we expect that  the people we help will go on to help others, so if we give someone a hand changing a tire, maybe they'll stop next time they see someone else, maybe even us, broken down on the side of the road.  You might know this concept, sometimes it's called the norm of reciprocity, sometimes it's called paying-it-forward.  

And then there's the social responsibility norm, which is the simple expectation that people will help those who depend on them, like any parent can expect to give more help than they're going to receive from young children.  That's just part of being a parent.  And that's really it, the world would be a delightful place if altruism were the standard for human behavior, but then, psychology wouldn't be nearly so interesting.

In some ways, you might say that what fuels conflict is the opposite of altruism: self-interest.  Social psychologists view conflict as any perceived incompatibility of actions, goals, or ideas.  That could mean two nations fighting over a border, sparring religious or political groups, or you and your boo fighting over whose turn it is to do the dishes.  And then a weird conundrum of human behavior: a lot of conflicts arise from what psychologists call 'a social trap', where people act in their own short term self-interest, even though it takes a toll on the larger group and on themselves over the long-term.  You see this kind of thing all the time on an individual scale, like in a crime movie, when a criminal just betrays all of his criminal friends to get the big payout, it doesn't turn out very well for him in the end.  But on a larger scale, you can find social traps taking their toll on the environment, like when we poach elephants to sell their ivory or cut down old growth forests to make a quick buck in the lumber market.  Either way, when self-interest succeeds in wrecking the collective interest by, say, depleting some limited resource, it becomes easy to start viewing our neighbors as competitors, taking us right back to the angora vs. out-group mindset that we all know causes big problems.

So as long as there's self interest, there's gonna be conflict.  But before you get all down on humanity, remember those Robber's Cave boys.  They were ready to go full-on Lord of the Flies before shared goals forced them to cooperate and ultimately, make peace.  The power of cooperation to make friends of former enemies is one of the most hopeful areas of psychological research.  If greed and self-interest can destroy the world, perhaps cooperation can save it.  

Today, you learned about the Robber's Cave experiment and what it taught us about realistic conflict theory and how shared goals can overcome conflict.  We looked at the physical and environmental triggers of aggression, and the frustration-aggression hypothesis.  You also learned about altruism, the bystander effect, and when we are more or less likely to help a person in need, and also about the social exchange theory, the reciprocity norm, the social responsibility norm, and social traps.  

Thanks for watching, especially to all of our Subbable subscribers who make CrashCourse possible.  To find out how you can become a supporter, just go to, and please remember to go to and subscribe for more future CrashCourses in the future.  This episode was written by Kathleen Yale, edited by Blake de Pastino, and our consultant is Dr. Ranjit Bhagwat.  Our director and editor is Nicholas Jenkins, the script supervisor and sound designer is Michael Aranda, and the graphics team is ThoughtCafe.  

(CrashCourse Endscreen)