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How do testosterone and other androgens affect male characteristics and behavior?

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Diagram comparing reproductive pathways: arrows show sexual reproduction forming a diploid zygote from oocyte and sperm, haploid parthenogenesis forming a haploid individual, and two types of diploid parthenogenesis-automixis and apomixis-both resulting in diploid individuals. Symbols indicate haploid and diploid stages. — Animal reproductive system The process of sexual reproduction and several forms of parthenogenesis.

In the context of the animal reproductive system, androgens—primarily testosterone—are essential for the development and maintenance of male characteristics and behaviors across many vertebrate species.12

Physical Characteristics

Androgens promote the development of male anatomy and secondary sexual characteristics. In humans, these include the growth of facial and body hair, deepening of the voice, and increased muscular and skeletal development. Testosterone also directs the development of the male reproductive tract, including the vas deferens and seminal vesicles, and supports spermatogenesis.234

Behavioral Influence

Androgens are closely linked to aggressiveness and sexual drive. In many species, aggression levels fluctuate in tandem with natural changes in testosterone; for example, castration often reduces aggression, while experimental reinstatement of the hormone restores it. These hormones also influence behaviors such as courtship, territorial defense, and vocalizations.24567

The relationship is complex and multidirectional: while androgens facilitate these behaviors, participation in social conflicts can also trigger rapid changes in hormone secretion. Furthermore, in some species, early exposure to androgens can permanently influence the nervous system, shaping adult behavioral patterns regardless of later hormone levels.56