Men have a psychological need to show off their courage and strength. When he sees you talking to another guy, that instinct kicks in and he jumps to protect you and prove he's worthy of your love.
Helen FisherScientists know that women gravitate to men who have a different immune system from theirs.
Helen FisherWe're not very dangerous animals; we don't have a horn like a rhino or quills like a porcupine.
Helen Fisher