NOTE: Some have argued that fish oils are oxidative upon digestion and that fish oil thus probably does significant aging and cellular damage internally that we may not yet understand. However, several studies suggest this to be a relative non-issue.  In addition, one study also found that additional Vitamin E can protective help overcome most of the small amount of oxidative damage that is done anyway. The study authors found that oxidative products in the urine "more than doubled when the fish oil capsules were introduced but then dropped by a factor of four when vitamin E was added. The vitamin E concentration in the red blood cells dropped very significantly when fish oil was ingested but more than recovered with the vitamin E supplement". 
The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.