Swinging dates back to many thousands of years ago, to the tribal age or mankind, which lasted much longer than the modern society where monogamous relations are proclaimed the only acceptable norm. Monogamy was only imposed upon women by law and religion relatively recently, because men wanted to make sure that their wealth was transferred to their own offspring and not to someone else’s. That’s why monogamy is one-sided: women are not allowed to be promiscuous, while men can get away with visiting brothels and having mistresses.
The length of the time that people have lived in a monogamous culture is relatively short compared to the history of polygamy. That is to say that polygamy and the need for a variety of sexual partners are more natural to humans than the society-regulated monogamy. Swinging lifestyle is only a reflection of this basic primeval instinct.
From what we’ve seen, swinger couples are much stronger and happier in general than non-swinger couples. It is widely known that the divorce rates and instability in regular marriages are very high and are only increasing every year. Swinging offers an outlet to release the powerful desires and fantasies that are stifled by conventional norms of behavior. If not fulfilled, the suppressed urges may result in disruption of relationships and even in mental disorders.This explains why so many couples secretly seek to play out the fantasies of exchanging partners with other couples. Sites for swingers are extremely popular.
Wikipedia says that:
Research on swinging has been conducted in the United States since the late 1960s. One 2000 study, based on an Internet questionnaire addressed to visitors of swinger-related sites, found swingers are happier in their relationships than the norm.
60% said that swinging improved their relationship; 1.7% said swinging made their relationship less happy. Approximately 50% of those who rated their relationship “very happy” before becoming swingers maintained their relationship had become happier. 90% of those with less happy relationships said swinging improved them.
Almost 70% of swingers claimed no problem with jealousy; approximately 25% admitted “I have difficulty controlling jealousy when swinging” as “somewhat true,” while 6% said this was “yes, very much” true. Swingers rate themselves happier (“very happy”: 59% of swingers compared to 32% of non-swingers) and their lives more “exciting” (76% of swingers compared to 54% of non-swingers) than non-swingers, by significantly large margins. There was no significant difference between responses of men and women, although more males (70%) than females completed the survey. This study which only polled self-identified swingers is of limited use to a broader application to the rest of society (external validity) due to self-selected sampling.