The Myth Of Monogamy

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From the issue dated April 20, 2001

http://chronicle.com/weekly/v47/i32/32b01601.htm

Deflating the Myth of Monogamy

By DAVID P. BARASH

The Nobel Prize-winning ethologist Konrad Lorenz used to recommend that every scientist discard at least one cherished notion every day, before breakfast. It is excellent advice (although Lorenz wasn't known for tossing away many of his ownprized ideas). In any event, good science doesn't really require that its practitioners intentionally turn their backs on what they believe to be true, or what they devoutly wish were so. Tincture of time and the accumulation of new findings generally accomplish that: If we wait long enough, the world has a habit of making mincemeat of even our most strongly held ideas. The only thing necessary is toremain open to the evidence.

Case in point: the widely held view that certain animals -- notably the great majority of bird species -- are monogamous. Second case in point: the belief that females of most species, including our own, strongly tend toward sexual fidelity -- in contrast to males, who are known to have a penchant for sexual variety, if not promiscuity.

Biologists have longunderstood that monogamy is rare in mammals. Of about 4,000 mammalian species, only a handful have ever been called monogamous. The tiny list includes beavers and a couple of other rodents, otters, bats, certain foxes, a few hoofed mammals, and some primates -- notably gibbons and the tamarins and marmosets of the tropical New World. By contrast, birds have long been the poster children of monogamousfidelity. A common figure, first reported by the great ornithologist David Lack in the 1960's, has been that 92 percent of the 9,700 bird species are monogamous. Picture an archetypal male and female robin, collaborating in nest building, then devotedly taking turns incubating the eggs and feeding their young.

The notion has even penetrated into popular culture. In the movie Heartburn, a barelyfictionalized account by Nora Ephron of her marriage to Carl Bernstein, the lead character complains to her father, who responds, "You want monogamy? Marry a swan!" Now we are learning that even swans aren't monogamous.

Actually, the myth of monogamy didn't disappear overnight. The tell-tale hiss of its deflation began several decades ago. One now-famous study, for example, sought to assessvasectomy as a possible means of population control among red-winged blackbirds. To their surprise, the researchers discovered that female blackbirds, mated to vasectomized males, were nonetheless laying eggs that hatched! Evidently, there was some hanky-panky going on in the blackbird world.

And not just blackbirds. By the 1980's, studies employing blood typing as well as analyses of proteinswere leading researchers to question whether social monogamy and sexual monogamy were necessarily synonymous. Then came DNA fingerprinting in the 1990's, and a veritable avalanche of new findings. Time and again, it was revealed that 10, 20, even sometimes 40 percent of nestlings were not fathered by the social father. The apparent mother, on the other hand, usually is what she seems to be,reinforcing the adage "Mommy's babies, Daddy's maybes."

Reports of extra-pair copulations -- henceforth, E.P.C.'s -- in animals previously thought to be monogamous have come hot and heavy during the last decade. Increasingly, biology journals have featured articles with titles such as "Behavioral, Demographic, and Environmental Correlates of Extra-Pair Fertilizations in Eastern Bluebirds," "Extra-PairCopulations in the Mating System of the White Ibis," "Extra-Pair Paternity in the Shag, as Determined by DNA Fingerprinting," "Genetic Evidence for Multiple Parentage in Eastern Kingbirds," "Extra-Pair Paternity in the Black-Capped Chickadee," "Density-Dependent Extra-Pair Copulations in the Swallow," and "Patterns of Extra-Pair Fertilizations in Bobolinks." We've even seen these oxymoronic...