Monogamy can be so difficult that its advocates have long pointed to the animal world to prove that the practice is not unnatural. If swans mate for life, the argument goes, humans ought to be able to do it too. But in a new book, The Myth of Monogamy: Fidelity and Infidelity in Animals and People, zoologist David Barash, 55, and his psychiatrist spouse Judith Lipton, 50, reveal that swans—as well as lovebirds, geese and other supposed paragons—are just as prone to secret trysts and jealous snits as humans. "Biology plays a big part in our behavior," says Barash. "To deny it is to bury our heads like an ostrich" (another faithless bird). The same evolutionary instincts that govern animal infidelity drive roughly 50 percent of husbands and 30 percent of wives into someone else's arms.
Yet humans can buck biology, say the authors, whose book incorporates Barash's 35-year study of 12 species as well as Lipton's clinical observations and other scientists' research. The couple, who have been married for 24 years, live in Redmond, Wash., and have two daughters, Ilona, 23, and Nellie, 16. Barash and Lipton discussed their findings with PEOPLE contributor Mary Boone.
Are any animals completely monogamous?
Lipton: Having only one sexual partner in a lifetime is extremely rare. More common is serial monogamy—remaining faithful to a person in a relationship or marriage.
Barash: Only one species is totally faithful: Diplozoon paradoxum, a tapeworm that lives in the intestines of fish. But that's because they have no choice: When they meet, they literally fuse together until death.
Why are animals unfaithful?
Barash: For male animals, just as for male humans, it's the opportunity to spread their sperm. Having many mates give birth to your offspring ensures your genes are passed along—the definition of success from an evolutionary standpoint. For females infidelity seems to be about "moving up"—finding a partner who offers better genes than her current mate or finding a male who has an especially good feeding territory. In humans a similar impulse may drive a woman to connect with a wealthy, successful man who can give her security.
What surprised you most in your research?
Barash: Not the male behavior, which is an old story. The startling news is that female animals mess around too. They're especially sneaky because their male mates are more likely to get violent with intruders. The reason biologists didn't know until recently about the adulterous sex lives of females is that they were keeping secrets from their mates and fooling human observers as well.
So how did scientists discover that the animals were cheating?
Barash: DNA. No matter how faithful, for instance, a ground squirrel parent appears, DNA will show that the offspring often was not fathered by the mate but by another.
Do animals feel jealousy?
Barash: Male animals are notoriously jealous. In fact, most of the within-species violence among animals is committed by males defending "their" women from the sexual advances of other suitors. But females are jealous too. House sparrows kill the offspring of strange females who mate with their husbands, and starlings aggressively flirt with their mates when another female shows interest.
Lipton: In many species besides our own there are two competing instincts within the brain. One is to be attracted to others and fool around, the other is to be totally outraged if your spouse or mate does the same. So jealousy is always present when there's sexual desire.
Is there an animal equivalent to philandering politicians?
Barash: In many species a socially dominant male has access to many partners. That's also the case with humans, even if we're not happy about it. Part of our fascination with Bill Clinton or Gary Condit is that many of us have been affected by infidelity. We work out our own feelings of anger and pain by watching the drama of unfaithfulness played out on a larger stage.
If monogamy is so rare in nature, is it a realistic goal for people?
Barash: Absolutely. Humans have the unique ability to know that with monogamy comes trust and love. Think of it as a mutual disarmament pact: I won't sleep around and make you crazy if you don't either. Both partners agree to forgo what may be biologically desired in the interest of the relationship.
How can people make monogamy work?
Lipton: Marry someone who is your best friend as well as your lover. He or she will show traits such as integrity, humor, empathy and a demonstrated willingness, even eagerness, to make the relationship work. Talk about sex and infidelity openly. Don't keep secrets or harbor grudges.
You two have remained truly monogamous?
Barash: Yes, but it hasn't been easy. Sex experts are human too.
On Newsstands Now
- Amy Robach: 'I'm Lucky to Be Alive'
- Paul Walker: Inside His Tragic Death
- Julia Roberts: Choosing Family Over Hollywood
Pick up your copy on newsstands
Click here for instant access to the Digital Magazine