"Little is known about the neurobiological pathways through which testosterone promotes aggression or about the people in whom this effect is observed."

Source : Using a Psychopharmacogenetic Approach To Identify the Pathways Through Which-and the People for Whom-Testosterone Promotes Aggression

This 2019 study published in the journal Psychological Science describes experiments attempting to explain chemical mechanisms, and links with Androgen Receptors (AR).

Testosterone appears to promote human aggression through an AR-related mechanism and to have stronger effects in men with the select personality profiles because it more strongly upregulates the subjective pleasure they derive from aggression. Given other evidence that testosterone regulates reward through dopaminergic pathways, and that the sensitivity of such pathways is enhanced among individuals with the personality profiles we identified, our findings may also implicate dopaminergic processes in testosterone's heterogeneous effects on aggression."
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Also see: Heat and Human Aggressionplugin-autotooltip__plain plugin-autotooltip_bigHeat and Human Aggression

It's often suggested that increased ambient temperatures tend to increase aggressive behavior in humans. There is, however, no generally agreed explanation for the phenomenon.

See: ‘Ambient Temperature and Horn Honking : A Field Study of the Heat/Aggression Relationship’ [ paywalled ] in: Environment and Behavior