cichlid fish spectators observing a winning fight, and soccer spectators seeing their team win the World Cup.
What many volumes of experiments reveal is that testosterone plays a fundamental role in social behavior across the animal kingdom, motivating individuals to defend their resources, acquire additional resources when possible, develop confidence following victory, and gracefully walk away following defeat. Testosterone influences behavior, and behavior influences testosterone. If an individual experiences a challenge, this causes an increase in testosterone. The increase in testosterone heightens confidence and risk-taking to defend the resources. Heightened confidence and risk-taking are often associated with winning fights. Winning fights increases testosterone, bringing us full circle to the challenges of social living.
Testosterone is joined by several other microcontrollers, including at least one additional hormone — cortisol — two neurochemicals — serotonin and dopamine — and several brain areas that are affected by these hormones and neurochemicals. Our understanding of this assemblage, beautifully synthesized by the psychologist Jack van Honk, accounts for both our adaptive and sometimes highly maladaptive capacity to harm others.
Cortisol mediates the stress response in fish, reptiles, birds, and mammals, including all ages of human mammals. When fear kicks in due to aggressive challenges from a dominant individual or from the appearance of a predator, cortisol rises. When individuals confront uncertainty, cortisol rises. When cortisol levels are high, individuals are more sensitive to punishment and more likely to avoid social interactions. Flipping the polarity around, when cortisol levels are low, individuals are more aggressive, more reward focused, and less sensitive to punishment. Testosterone and cortisol therefore play within the bodies of animals like two children sitting on opposite ends of a see-saw. When testosterone is up and cortisol is down, individuals are primed to harm others and take risks. When testosterone 1s down and cortisol is up, individuals are risk averse, less likely to harm and more likely to engage in fnendly social behavior.
Serotonin, as noted earlier in the discussion of domestication, is primarily involved in self- control. High serotonin levels are associated with behavioral inhibition, whereas low serotonin levels are associated with disinhibition or impulsivity, as well as heightened aggression. Dopamine is linked to the experience of reward, both in terms of predicting when it will occur and in motivating behavior that maximizes the odds of obtaining the goods. When animals reach their goals or expect to obtain them, including food, mating, or winning a fight, the brain delivers a surge of dopamine. In humans, taking a drug that increases the amount of dopamine, causes people to believe that they will feel more elated about
an event in the future.
Hauser Chapter 1. Nature’s secrets 37
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