By the end of the 20th Century, scientific research on animal behavior and brain chemistry were providing strong confirmation of the troubling observation many of us had already made through personal experience - that life long monogamy is not natural for humans, nor for most other animals.

As David Barash and Judith Lipton discuss in their book The Myth of Monogamy which was published in 2001, the advent of DNA testing to determine paternity was a major breakthrough in the study of animal mating patterns. Many species previously thought to be monogamous have since been found to be socially monogamous at best. That is, they may mate with a single individual, setting up housekeeping, co-parenting, and sharing resources. But DNA testing along with behavior observation reveals that in many species both males and females have “secret affairs” often with other partnered individuals.