The daddy-at-home theory posits that concealed ovulation evolved to promote monogamy, to force the man to stay home, and thus to bolster his certainty about his paternity of his wife's children. The many-fathers theory instead posits that concealed ovulation evolved to give the women access to many sex partners and thus to leave many men uncertain as to whether they sired her children.

Sex in social mammals is generally carried out in public, before the gazes of other members of the troop.

Recreational sex is thus supposed to function as the glue holding a human couple together while they cooperate in rearing their helpless baby.

Sex is flagrantly separated from reproduction in a few species, including bonobos and dolphins.

big-bang reproduction, or semelparity: a single reproductive effort, followed by preprogrammed death.

But the largest number of primate species--thirty-four--have a promiscuous system in which females routinely associate and copulate with multiple males.