Though marriage is universal and monogamy is the dominant form, it remains a puzzle why marriage should exist at all. Evolutionary biologists assume that human fitness is measured by how many of one's genes are reproduced into the next generation. If that is true, men should seek out as many sexual partners as they can, because, in exchange for a few minutes of rather pleasant effort, they can multiply the number of their offspring. Therefore, in a world simply governed by evolutionary rules narrowly defined, men should seduce as many women as possible without much regard for a marital bond. The reason it prevails is not that it is about sex but that it is about children and property.
Human marriage is a reproductive alliance.
The Enlightenment gave a powerful boost to human choice and to freedom from dogma and tradi tion. In the late eighteenth century, various writers, such as the Scotsmen David Hume and Adam Smith, explained that human life could be understood by human reason alone. They wrote on the assumption that the family was of great importance but could be taken for granted. Smith understood that the need to care for the young was the chief reason for marriage. But he assumed that the affection on which marriage was based would persist beyond child rearing.