Testosterone has been discussed on here loads of times before but people seem to ignore the bits they don't like. As I've got to be up at 4am, I'm going to be lazy and just cut and paste a post from a previous thread.
There's a lot of evidence to suggest that testosterone is a significant factor in human aggression, although some studies have concluded that high testosterone alone isn't always a predictor of aggression - like how some dog breeds have a greater capacity for aggression but are not always aggressive as individuals.
"When male robins enter the breeding season, their testosterone level rises. They become aggressive and amorous. Testosterone has remarkably similar effects on men."
www.psychologytoday.com/us/blog/the-human-beast/200907/sex-violence-and-hormones?amp
"In non-human animals, the relationship between testosterone and aggression is well established."
www.sciencedirect.com/science/article/pii/S135917890000032X
"There is evidence that testosterone levels are higher in individuals with aggressive behavior, such as prisoners who have committed violent crimes."
www.ncbi.nlm.nih.gov/pmc/articles/PMC3693622/
"We were able to show for the first time that increasing levels of testosterone within the normal physiological range can have a profound effect on brain circuits that are involved in threat-processing and human aggression."
www.elsevier.com/about/press-releases/research-and-journals/testosterone-in-healthy-men-increases-their-brains-response-to-threat
"Inmates who had committed personal crimes of sex and violence had higher testosterone levels than inmates who had committed property crimes of burglary, theft, and drugs. Inmates with higher testosterone levels also violated more rules in prison, especially rules involving overt confrontation."
www.sciencedirect.com/science/article/pii/019188699400177T
"Higher testosterone levels are related to criminal violence and aggressive dominance among women in prison."
www.sciencedaily.com/releases/1997/09/970927110900.htm