n.
A theory that explains why the presence of a second male in a sexual scenario with a woman increases rather than decreases the arousal of a heterosexual male.
The presence of a second male causes the first male's testes to increase sperm and
testosterone production. This evolutionary reaction occurs so that if they both engage in intercourse with her, his increased erection size and sperm count will boost his chances of inseminating her over his reproductive
competition.
Although the reaction is most powerful in person when a second male's pheromones are present, just seeing another male's erect phallus through any type of media will trigger the reaction.
When the other male ejaculates, the first male's reaction surges, giving him an
overwhelming urge to also ejaculate even if his penis is nowhere near a vagina or other orifice.
