Final answer:
Testosterone and serotonin levels, as well as hormonal changes, can affect aggression.
Step-by-step explanation:
The biological explanation for aggression is influenced by various factors. One factor is testosterone, a hormone that is often associated with aggression. However, research has shown that the relationship between testosterone levels and aggression is not always clear, as there are other factors that contribute to aggressive behavior. For example, roosters given testosterone shots may act more like hens, which suggests that testosterone can actually reduce aggression in some cases (option a). Men undergoing sex change may experience a decrease in aggression (option b), while women undergoing sex change may exhibit more aggressive behavior due to hormonal changes (option c). Finally, studies have shown that people with lower levels of serotonin are more likely to display aggressive tendencies (option d). Therefore, options a, b, and d all provide a biological explanation for aggression.