Why is the connection between testosterone and aggression more complex in animals with elaborate social structures?

In species with elaborate social structures, the connection between testosterone and aggression is more complex because the influence of the hormone is less direct and less dependent on gonadal production alone.1

While castration typically reduces aggression in many vertebrates, this effect becomes significantly less drastic as social complexity increases. This suggests that in these species, aggressive behavior is governed by a more intricate interplay of factors beyond simple hormonal levels, including:1

• Multidirectional Feedback: The relationship between hormones and behavior is bidirectional; while testosterone influences aggression, the outcome of social conflicts—such as winning or losing a fight—rapidly alters an individual's hormone secretion, which then modulates future behavior.1
• Alternative Hormonal Pathways: Aggression can be facilitated by nongonadal hormones, such as those produced by the adrenal gland, or modulated by neuropeptides like vasopressin and arginine vasotocin within the limbic system.1
• Past Experience: Behavior in conflict situations is highly adaptive, shaped by both current circumstances and an individual's history of social interactions.1