Before we attempt to answer the question of why a couple might choose to swing, it should first be noted that - simply - monogamy is unnatural. It's true. Considering all the forms of life in nature, monogamous behavior should be properly be regarded as extremely deviant...

LG, may we attempt to say this in the most articulate manner possible: Right On! Your in depth (and of course, unbiased) research into human (and cannine) sexual behavior, coupled with your sharp analytical prowess, has uncovered some long-held myths and exposed our innermost tendencies and desires. Kudos and keep up the good work!

You hit the nail on the head. Monogamy is indeed unnatural feven or married couples that have taken the vows. Almost all men and women, married or not do covet someone else's wife or significant other in a sexual way. It is the variety of sexual experience that we all desire. This enriches our life sexually and otherwise when couples swap partners for erotic fun, teasing and sexual intercourse.