In 1935, renowned anthropologist Joseph Daniel Unwin tried to prove the opposite: that marriage was an irrelevant and even harmful cultural institution. He was forced by the evidence to conclude that only marriage with fidelity, what he called absolute monogamy, would lead to the cultural prosperity of a society. Anything else, such as “domestic partnerships” would degrade society.
In his address to the British Psychological Society, Unwin said this:
The evidence was such as to demand a complete revision of my personal philosophy; for the relationship between the factors seemed to be so close, that, if we know what sexual regulations a society has adopted, we can prophesy accurately the pattern of its cultural behavior…
Now it is an extraordinary fact that in the past sexual opportunity has only been reduced to a minimum by the fortuitous adoption of an institution I call absolute monogamy. This type of marriage has been adopted by different societies, in different places, and at different times. Thousands of years and thousands of miles separate the events; and there is no apparent connection between them. In human records, there is no case of an absolutely monogamous society failing to display great [cultural] energy. I do not know of a case on which great energy has been displayed by a society that has not been absolutely monogamous…
If, during or just after a period of [cultural] expansion, a society modifies its sexual regulations, and a new generation is born into a less rigorous [monogamous] tradition, its energy decreases… If it comes into contact with a more vigorous society, it is deprived of its sovereignty, and possibly conquered in its turn.
It seems to follow that we can make a society behave in any manner we like if we are permitted to give it such sexual regulations as will produce the behavior we desire. The results should begin to emerge in the third generation.
”Sexual Regulations and Cultural Behavior,” Joseph Daniel Unwin, Ph.D., in an address given to the Medical Section of the British Psychological Society. Library of Congress No. HQ12.U52
Sex is an instinct that produces an institution; and it is positive and not negative, noble and not base, creative and not destructive, because it produces this institution. That institution is the family; a small state or commonwealth which has hundreds of aspects, when it is once started, that are not sexual at all. It includes worship, justice, festivity, decoration, instruction, comradeship, repose. Sex is the gate of that house; and romantic and imaginative people naturally like looking through a gateway. But the house is very much larger than the gate. There are indeed a certain number of people who like to hang about the gate and never get any further.
In a 2007 article (now in his website archives), atheist Richard Dawkins frowned upon those valuing faithfulness. In “Banishing the Green-Eyed Monster,” he asked, “Why are we so obsessed with monogamous fidelity in the first place?” He says that we need to intellectually “rise above” the sexual jealousy that blind Darwinian evolution has produced in us and cheerfully permit our spouses to carry on any sexual recreation they choose to have outside the marriage bed. “Why should you deny your loved one the pleasure of sexual encounters with others if he or she is that way inclined?” he asks. Dawkins is being completely consistent with his worldview by denying any objective sexual morality, even where marriage is concerned, so long as no one is harmed. (It remains unclear, however, why harming anyone or anything is objectively wrong in his view, where morality is nothing but an evolutionary social construct.)
My sense is that most self-described atheists, particularly those who are in happy marriages, have a deep-seated conviction that something is truly wrong with marital infidelity. As God’s image-bearers, the Truth of Things resonates strongly within their soul, and they know that spouses should be faithful. Just like they know, intuitively, that it is wrong to stab puppies with scissors for fun. The Apostle Paul talked about how even those who do not profess to follow God often still follow His law, for it is written on their hearts—“their conscience bearing witness and their thoughts alternately accusing or else defending them” (Romans 2:15).