Dolphins engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins engage in such acts of aggression apparently for the same reasons as humans: disputes between companions and competition for females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile as a result of losing a fight.
Male bottlenose dolphins have been known to engage in infanticide. Dolphins have also been known to kill porpoises for reasons which are not fully understood, as porpoises generally do not share the same diet as dolphins, and are therefore not competitors for food supplies.
Dolphins are known to have sex for reasons other than reproduction, sometimes also engaging in homosexual behavior. Various species sometimes engage in sexual behavior including copulation with other dolphin species. Sexual encounters may be violent, with male dolphins sometimes showing aggressive behavior towards both females and other males. Occasionally, dolphins behave sexually towards other animals, including humans.