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Video transcript

- [Voiceover] Psychologists define aggression as any physical or verbal behavior that's intended to harm or destroy. So things like physical assault or verbal assault or even spreading a malicious rumor would all count as aggression. And while they can spend a lot of time thinking about different aggressive actions, I think a more important question is where aggression comes from. And there seem to be three things that can influence it. The first is biology, the next is psychological, or cognitive influences, and the last are socio-cultural influences. And while none of these things on their own might lead to aggression, a combination of the three of them is what we think leads to aggressive behavior. And, the first one I wanna talk about is biology. And, there are actually three different components of biology that I would like to discuss. The first one is genes, and we know that there needs to be a genetic component to this, because animals can be bred for aggression. But, there's some other evidence too. We know that if one identical twin has a violent temper, the other one is likely to have one as well. But, the same is not true for fraternal twins. Another important biological factor could be the impact of brain structure on aggressive behavior. Now, there's now one spot in the brain that controls for aggression, but there are circuits that can either inhibit or facilitate it. And so, what we're looking at here is what we would see if you cut someone's brain directly in half. So, if you can imagine a person's face, what we've done is we've cut straight down the middle and pulled the two sides of the head apart. And, we refer to this kind of slicing as a sagittal slice, and this one in particular is referred to as a mid-sagittal slice, because it was taken right down the mid-line. And, just to help orient you with this image, this would be the front of the brain, the back of the brain, the top of the brain, and the bottom of the brain. And the first brain area I wanna talk about is the amygdala. And, this small brain structure is actually really important, because it helps facilitate our fear response. And when stimulated, it tends to trigger aggressive behavior. Another area of the brain that seems to facilitate aggression is the frontal lobe which would be located here. And, this part of the brain is responsible for a lot of really important high-order tasks, things like planning and decision-making, but another thing that it's responsible for is impulse control. And, studies of violent criminals have shown decreased frontal lobe activation. And, we can't really draw any firm conclusions about that because it's correlational. But, it does seem to imply that maybe those who commit violent actions will have trouble inhibiting aggressive behaviors that other people might be able to keep inside. Another biological factor that can influence aggression is testosterone. And, testosterone is a hormone that's released both by the testis in men and the ovaries in women. And, this might be kind of surprising to you, because we usually associate testosterone with men and estrogen with women, but the truth is that testosterone is present in both. However, it is higher in men which is one of the things that leads men to be more aggressive than women. This is also one of the reasons why a 70-year old man would be less aggressive than a 17-year old adolescence, because men's testosterone production decreases over time. Testosterone is a really important hormone though, and it influences way more things than aggression. And because of this, scientists have actually found that they can predict aggressive behavior based on the other signs of testosterone. So, let me break that down. We know that high levels of testosterone can lead to aggression, however, we also know that high levels of testosterone are involved in muscle building, as well as things like determining the shape of the face. High levels of testosterone tend to result in wider faces as opposed to rounder long ones. And, because of this, a very muscular physique and a very wide face tend to be fairly good predictors of aggression. High testosterone also has a number of other effects that might lead to aggressive behaviors. For example, it can sometimes lead to irritability and assertiveness and impulsiveness, even a low tolerance for frustration. And, all of those things in combination might lead someone to act aggressively. We also know that drugs that reduce testosterone levels tend to reduce aggressive tendencies which adds further proof to the idea that testosterone plays a large role in aggressive behaviors. There are also a number of psychological factors that can lead to aggression. And, a lot of these are based on what we refer to as the frustration-aggression principle. And, this is the idea that frustration creates anger which can then spark aggression. And, we know that almost anything can cause frustration, things like physical pain or the presence of crowds. But, one main unexpected frustration that tends to lead to aggression might surprise you and that's temperature. And, we know from experiments that have been done in a lab that the higher the temperature in the room, the more frustrated a person left alone tends to become. And, we also know by examining crime records that there tend to be more violent crimes when the weather is hot as compared to when it's cold. We also know that reinforcement and modeling can lead to aggression. In terms of reinforcement, when being aggressive pays off, we're likely to be aggressive again. So, parents who reward temper tantrums by giving in to the child's demands, are actually encouraging more temper tantrums in the future. Parents can also model aggressive behavior for their children. If parents deal with restraining situations by fighting and yelling at each other or even screaming and hitting, children are likely to demonstrate those behaviors as well. So, even if a parent never yells at a child and doesn't reinforce their aggression in any way, the child is still paying attention to what the parents do, and it can pick up their behavior just by observing them. The last thing that I wanna talk about are social-cultural influences on aggression. And, these are things within our society that tend to bring out aggressive behavior in people. For example, we know that people tend to act more aggressively in groups compared to how they would react if they were just by themselves. Think about how some towns react after losing a big game. People can riot in the street, they can set cars on fire, and afterwards, all everyone can talk about is how they don't understand how something like that could happen there, because it's not a bad place, it's not a violent town. But, what they're seeing here is what's referred to as deindividuation which means that we gain kind of an anonymous status when we're with a large group of people. And so, of other people around an individual are behaving poorly, then they may tend to act poorly as well. This also helps to explain why some people tend to demonstrate poor behavior on the internet. For example, think about YouTube comments. There're some things that people say online that they would never even dream of saying to another person if they were face-to-face. But, because they're online, and because they're kind of anonymous, and because those around them might be modeling poor behavior, they tend to display poor behavior as well. And talking about the internet or media in general, actually brings up another social factor that can lead to aggressive behavior. And, that's social scripts. When people find themselves in new situations and they're unsure of how to behave, they tend to rely on social scripts, or instructions that are provided by society about how to act. So, let's say someone watches a lot of violent media. Let's say that they watch a lot of violent movies, or maybe they play a lot of violent video games. Even though, that media doesn't tell them that that aggressive behavior is okay, it's still modeling that aggressive behavior for them. It's still showing them that people are responding to situations in an aggressive way. And so, when someone is placed in a new situation, and they're uncertain about how to behave, they might rely on this social script to tell them how to act, and so, maybe they'll lash out at another person when something goes wrong. And, this isn't to say that violent media causes aggression, so much as viewing that media can give someone just one example of how they might act in frustrating situations. And, I wanna take a moment to address all of these different topics, because psychologists are not saying that any one of these things could cause aggression. Instead, it seems to be that a combination of biological, psychological, and social factors tend to work together to lead to aggressive behavior.