I want to first mention that both violence and aggression is defined in term of culture and as such is a difficult subject for researcher to define in studies.

I want to first mention that both violence and aggression is defined in term of culture and as such is a difficult subject for researcher to define in studies. The link between aggression and testosterone in modern studies is a complicated one. The theory that testosterone levels can be used as a predictor for violence has been extensively debunked. However violence is a predictor for high testosterone, a finding mostly done on apes. The prevailing theory, as far as I seen in modern research, is the challenge hypothesis. If two males fight, the winner of the two will have raised testosterone afterward. The winner will also be more likely to be more vigorous defending themselves if their new won status is challenged. On a more subtle human experience, place people in a economic game and inject some with testosterone. What ever behavior that the game has in order to defend status will be increased in those injected. If status is preserved by giving money, those injected with testosterone become more generous. A similar study has been done on sport fans. When a team wins a match, male fans of that team will have their testosterone raised afterward. If there is a confrontation between fans of the two different teams, it is more likely that the winning side will react more aggressively. Talking about toxic behavior, there is also a similar finding for women. It is however a bit more complicated and involve multiple hormones. The aggression is also more complicated, harder to define, and is more context sensitive.