____ behaviour depends on the individual as well as the situation.
Most of the vigourous emotional behaviours we observe in animals fall into the categories of attack and escape, and it is no coincidence that we describe the ____ nervous system as the fight-or-flight system. These behaviours and the corresponding emotions – anger and fear – are closely related both behaviourally and physiologically.
Why do some people turn ____ more readily than others? Some environmental factors are easy to identify. Certainly people who were abused in childhood, people who witnessed violent abuse between parents, and people who live in a violent neighbourhood are at greater risk of violence themselves.
Another environmental factor is exposure to ____, which is harmful to developing brains. Since the banning of lead-based paints and the rise of unleaded gasoline, the prevalence of violent crime has declined, possibly as a result of the decreased lead in the environment.
What about ____? Monozygotic twins resemble each other more closely than dizygotic twins do with regard to violent and criminal behaviours, and adopted children resemble their biological parents more closely than the adoptive parents.
However, various kinds of aggressive behaviour to occur under different circumstances, and we cannot expect to find a single ____ or set of genes that will account for all variations.
After researchers repeatedly failed to find a strong link between any single gene and aggressive behaviour, they explored the possibility of interactions between heredity and ____.
Several studies have found that violence is particularly enhanced in people with both a genetic ____ and a troubled early environment.
The effects of genetic differences can be seen in the production of the enzyme __________ (MAOa).
monoamine oxidase A
The enzyme MAOa breaks down the ____ dopamine, norepinephrine, and serotonin, thus lowering the available amounts. The effects of this gene apparently interact with childhood experience.
Among those who were seriously maltreated in childhood, the rate of antisocial behaviour was significantly higher for those with ___ MAOa activity.
Male ____ behaviour depends heavily on testosterone, which is highest for adult males in the reproductive season. Even in species that do not have a particular season for breeding, testosterone increases are linked with increased striving for social dominance.
Similarly, throughout the world, ____ fight more often than ____, commit more violent crimes, shout more insults at one another, and so forth.
men : women
Moreover, young adult men, who had the highest ____ levels, have the highest rate of aggressive behaviours and violent crimes.
According to the "____ ____ ____", the reason testosterones effects are unimpressive is that violence depends on the other chemicals as well, especially cortisol and serotonin.
triple imbalance hypothesis
____, which increases under stressful conditions, increases fear, and a decrease in cortisol is associated with loss of inhibitions.
Therefore, aggression tends to be ____ when testosterone levels are high and cortisol levels are low.
Men with high levels of both testosterone and cortisol are likely to ____ their violent impulses.
_____ also tends to inhibit violent impulses.
Several lines of evidence link aggressive behaviour to ___ serotonin release.
When neurons release serotonin, they ____ most of it and synthesise enough to replace the amount that washed away. Thus, the amount present in neurons remains fairly constant, and if we examined that amount, we have little idea of how much the neurons have been releasing.
However, if we measure the serotonin metabolites in the body fluids, we gauge the ____, which is the amount that neurons released and replaced.
Researchers estimate serotonin turnover from the concentration of ___________ (5-HIAA), serotonins main metabolite, in the cerebrospinal fluid (CSF).
In mice, ____ ____ lowered serotonin turnover by the greatest amount in the genetic strains that reacted with the greatest amount of fighting after social isolation.
That is, serotonins effects _____ with those of testosterone, as in the triple imbalance hypothesis mentioned previously.