Early Primates | | UZH
Religious fundamentalists like to assume they have ownership of the institution of marriage because the 'right' form of marriage was dictated by their imaginary god so we should all subscribe to their approved form of it. In many formerly majority Christian countries, the Christian-based marital laws are one of the few remaining vestiges of a time when Christianity imposed itself on everyone, believers, non-believers and non-Christians alike, arrogantly believing it had a divine right to rule.
But recent research has shown that a form of flexible monogamy, or more or less stable social parings of a female and a male is common if not the norm in the primate family. It was most likely incorporated into religions because some human tribes thought of monogamy as the 'right' form of sexual relationship, so any god whom the priesthood wanted to be taken seriously had to hand down 'morals' that the people thought were right and proper. After all, the only way to tell if a god is a good god or an evil god is to compare its morals and behaviour to that of an external standard of 'good', is it not?
If you think not, you have to believe that if your god had told people to hurt babies, rob banks and hit old ladies, those would now be considered moral acts and people who didn't do them would be regarded as immoral and deserving of punishment or other social sanctions. Christian apologist for faith-based genocide, William Lane Craig, has even declared that a seemingly immoral act such as infanticide, is morally right if you believe his (but only his) god commands it, and it would be immoral not to carry out such a divine command.
But William Lane Craig's repugnant idea of what constitutes morality is straying somewhat off the point, which is the 'right' form of marriage in human society, which William Lane Craig presumably believes is divinely commanded by his god and therefore mandatory for the rest of us.
But, absolute monogamy is not the universal norm in modern human sexual relationships, even in societies which only permit monogamous marriage, and probably never has been. Humans can best be described as mostly monogamous, most of the time, with 'infidelity' by both sexes being fairly common to the extent that some estimates put the number of people who have a different father to the one they think is theirs at about 25%. In some cultures, such as Islamic, bigamy is normal and, as evidenced by baptism records, pre-marital sex was commonplace in 19th Century England.

























