earnest_voice
Well-Known Member
http://www.rmca.org/Articles/aggression.htm
Some studies show that there are also differences in circulating testosterone levels between strains of rats, the more aggressive animals having higher testosterone levels and vice-versa. Interestingly, it has also been observed that individually-housed rats attack intruders more readily than rats that are housed in groups. In rats, exposure to androgens (the male steroids testosterone and dihydrotestosterone) during fetal development determines the number of cells produced in a part of the brain termed the sexual dimorphic nucleus.