In the movie "Heartburn," a fictionalized account of Nora Ephron's ill-fated marriage to Carl Bernstein, the distressed protagonist (played by Meryl Streep), tells her father of her husband's infidelities. "You want monogamy?" her father chides, "Marry a swan."
But swans, biologists now know, are not monogamous either.
This and an avalanche of revelations about birds and mammals long believed to be noble paragons of monogamy are explored in "The Myth of Monogamy" (W.H. Freeman & Co., 2001).
The book--written by David P. Barash, a zoologist at the University of Washington in Seattle, and his wife, Judith P. Lipton, a psychiatrist--is a lively look at what the latest research has revealed about the "surprisingly weak biological underpinnings of monogamy."
Barash's inspiration for the book came after a surge in DNA testing in the 1990s was used in biological studies to determine the paternity of offspring in species long-considered monogamous. Scientists repeatedly found that the females of species thought to be monogamous were bearing offspring fathered by males other than their mates. (In the very unsexy terminology of biologists, the creatures were engaging in "extra-pair copulations.")
"What biologists never had until now was clear evidence of paternity," said Barash. "Now when we do DNA tests, animals that we thought were beautiful poster children of fidelity, we find out, over and over, that there is an awful lot of hanky-panky going on."
Of the approximately 4,000 mammalian species, only about 3% are now considered to be monogamous. These include beavers, otters, bats, some rodents, certain foxes and a few hoofed-mammals, said Barash. Only 9% of the approximately 100 primate species are considered monogamous.
In the 1960s, said Barash, birds became the biological standard-bearers of monogamy after famed ornithologist David Lack reported that 92% of the 9,700 bird species were monogamous. However, DNA testing has since revealed that sometimes as many as 40% of hatchlings of various bird species do not share DNA with the bird presumed to be the father.
So what does the extra-pair philandering of birds and beasts have to do with humans?
Human beings, like most animals, have never really been successful at monogamy either, said Lipton. People are notoriously deceptive when asked about sexual affairs, said Lipton, and for obvious reasons. Sexual infidelity is at the root of most divorces, she said. According to one study, 50% of married men reported having at least one extramarital affair, compared with 30% of women. The figures are unreliable because men generally inflate reports to look more manly, said Lipton, while women deflate them to guard their reputations.
Among roughly 185 human societies surveyed by an anthropologist and a psychologist, fewer than 16% restricted members to monogamy, according to the book. And two-thirds of those monogamous societies tolerate premarital and extramarital sex.
It is difficult to know when monogamy emerged as a marriage system, said Barash. "A number of current hunter-gatherer tribes practice monogamy, so there is reason to believe monogamy predated biblical times. Monogamy as a societal norm probably dates back to the late Middle Ages when the Catholic Church espoused it."
Monogamy may not be natural, and humans may be failing at it, said Lipton, but it is undoubtedly the better of a number of flawed marital systems, including open marriage, group marriage and polygamy, which, said Barash, "founder on sexual jealousy."
"The paradox." he added, "is that evolution produces individuals who are inclined to have a wandering eye, but they are also inclined to be very jealous and driven crazy."
Monogamy is also considered the best path to a mature, deeper love than, say, the love one feels in a quick sexual liaison with someone new and attractive, said Barash. The authors are themselves an example. They have been married for 25 years, raised two children, and claim to have withstood temptation.
They hope the book will serve as an open letter, a kind of warning to starry-eyed lovers lulled into the dreamy ideal that once married to a "soul mate," neither partner will sexually yearn for another or, God forbid, actually have an affair.
"The perfect fit of a good monogamous marriage is made, not born," the authors warn. Equipped with an understanding of human sexual instincts, Barash said, couples may be better armed to endure the difficulties of monogamy and to resist the temptations of, as he put it, lots of "cute people."
"What challenges monogamy the most is our own human inclinations, our own biology," said Barash. "When it comes to maintaining monogamy, we should know our own shared human instincts are the weakest link."
David Barash and Judith Lipton will discuss their book from 2 to 4 p.m. on June 2 at the Los Angeles Museum of Natural History, 900 Exposition Blvd., Los Angeles.