Men and women dream differently. Women tend to recall their more often than men and women tend to report more frequent and more intense than men. Men dream more often about other men rather than women, whereas women dream equally often about men and women. For example 67% of characters in men's dreams are other men whereas 48% of characters in women's dreams are other women. Men tend to dream about aggressive encounters with other men (typically strangers) while women tend to dream about interactions with familiar others that take place in familiar surroundings.

Why do these consistent differences occur in dreams? One possibility is that men and women are socialized differently as they grow up-boys are taught to be more aggressive than girls, and girls are taught to be more social than boys -or so the story goes.

But there is plenty of evidence to suggest that boys do not need to be taught to be aggressive and girls do not need to be taught to be social. The biologies of boys and girls propel boys and girls down these sort of developmental trajectories. While the trajectories are not inevitable and deterministic, they are real tendencies.

Thus, the dream recall and dream content patterns of men and women differ because the biologies of men and women differ. Why would Mother Nature tend to increase physical levels in boys and verbal social interactions tendencies in girls... to put it in crudely simplistic terms?

Sexual selection theory (a branch of evolutionary theory) suggests (to again put the matter in crudely simplistic terms) that females are the choosy sex in humans and that men must outcompete one another in order to gain favor with women. Just as male reindeer bucks or male mountain goats grow huge weapons we call antlers in order to battle with other bucks (typically in front of a receptive female) during the season so too do human males cultivate innate tendencies to physical aggression in order to outcompete other males in the battle to gain the favors of local females...or so the sexual selection story goes.

Whether or not the sexual selection theory makes sense it is clear that for many millennia men have gone off to war while women watched over the kids at the homefront. This ‘war theory' regarding high physical aggression levels in males suggests that men HAD to become aggressive in order to survive-not just to impress women, as the sexual selection theory suggests. The data from dream content studies is consistent with both the war theory of male aggression and the sexual selection theory. We need further studies in order to come to an understanding of this intriguing sex difference in dream content.