Why do human beings have sex? Is it to reproduce offspring? Yes. Is it to create, indelible bonds of attachment in relationships? Yes. It is to satiate physical needs, urges and desires? Yes. These queries can snowball into a Sigmund Freud vs Carl Jung match, in a hurry. But even then, it won't really answer the question in entirety. Why do human beings have sex? Part of the carnal act belongs to an often unspoken truth. Social hierarchy. Unlike in nature and with other animals, human beings don't establish dominance in a food-chain based system of hierarchy.