Birds Do It
In the animal behavior class I teach, students seem interested in one thing above all others: infidelity. As one student put it recently: “Last night on TV they said that cheating on your spouse is natural, because animals do it, so you expect people to do it too. Are we going to talk about that in class?”
In fact, it is something we talk about in class--although not in the way it’s discussed on late-night television. Since the advent of DNA-based paternity analysis, scientists have begun intensely studying infidelity in animals, particularly in birds. It is now relatively easy to sample the DNA from a set of chicks in a nest and compare it with the DNA of the male and female associated with the young. As it turns out, so-called extra-pair paternity is quite common among birds. The percentage of offspring sired by males other than the one attending a female and her nest varies widely from species to species, from 0% in snow geese to a whopping 90% in a species of brilliantly colored Australian fairy wren.
This discovery was quite a shock to scientists because outwardly it appeared that most birds were monogamous. Birds have always looked so admirable, so industrious. The way the male and female rush back and forth to their demanding brood of chicks seems like nature’s model of good parenting. And now we find that they’re actually in the same situation as millions of modern-day husbands and wives, eyeing a child warily and making uneasy jokes about the milkman.
My students are no less shocked than the scientists. In fact, they are horrified. If warblers, robins and other models of monogamy are doing it, they worry, do we then have to conclude that extra-pair copulation--or adultery--is natural and expected, part of our evolutionary heritage and therefore nothing to make a fuss about?
But the truth is, the birds aren’t “cheating”; they are just doing what they do. They don’t have rules about the pair bond between a male and female, and it isn’t cheating if there are no rules to break. If we try to use their behavior as a model or justification for our own, we might find ourselves making decisions about morals on very shaky grounds. Because chimpanzees masturbate publicly, does that mean humans should?
We can make lists of things humans do that animals don’t--pay taxes, watch television, wear socks--or things they do that we don’t--lay eggs, change the color of our skin to match our surroundings, store sperm in the uterus for years. We are understandably fascinated with the attributes we share with some animals, like mate choice, parenting and craving sugar. But trying to model our behavior on the traits of other species is pointless. It brings to mind a new version of an old parental admonition: “If all the lemmings jumped off a bridge, would you jump too?”
In the end, modeling human behavior on animal behavior is absurd because for each species that exhibits an “admirable” behavior by human standards, you can probably find one that’s “contemptible.” And it’s equally silly to be disturbed by what the animals do. Yes, we’ve discovered some philandering finches, but real, true, till-death-do-us-part monogamy is still seen among many animals, including snow geese and some sea birds.
Still, humans of all ideological stripes seem to feel compelled to assert that their viewpoints are supported by nature itself. Traditionalists note that, with few exceptions, males in nature are physically larger and behaviorally dominant--at least in many vertebrates--and that females tend to play the dominant role in nurturing infants. Feminists respond by noting nature’s exceptions--bonobos have lesbian sex, females in most species are the sex that does the choosing during mating. And of course feminists can usually end the discussion by bringing up the example of praying mantids, whose females eat the males after mating.
Ultimately, though, these arguments are pointless. Humans live in societies of their own making, and we have shaped society’s rules not so much to conform to nature but in pursuit of the common good. Murder is illegal because it destabilizes society. So what if intra-species killing is common in certain parts of the animal kingdom? I like to think we are perfectly capable of choosing our own visions of an ideal society without the help of snow geese or wrens.
As a scientist studying animals, not humans, I am also concerned about how our preconceptions of what constitutes acceptable human behavior affects our views of animal behavior. Some of the early papers on extra-pair paternity in birds were positively Victorian in their assignments of blame. Initially, there seemed to be two approaches, neither one particularly favorable to females. Either the males were roaming around taking advantage of hapless females waiting innocently in their own territories for the breadwinner males to come home with the worms or else females were brazen hussies, seducing blameless males who otherwise would not have strayed from the path of moral righteousness into turpitude. One scientist referred rather peevishly to “female promiscuity” in blackbirds. Another article, published in the prestigious journal Nature, dubbed young warblers fathered by males not paired with the mother “illegitimate,” as if their parents were supposed to have acquired tiny avian marriage licenses and chirped their vows.
Such prejudices are amusing, but I worry about how they spill over and influence our interpretation of what we see animals doing. A paper on Tasmanian native hens, birds with a complex set of relationships between the sexes, discussed what appears to be polyandry, multiple males associated with a single female. The paper refers to this behavior as “wife-sharing.” I have never seen the phenomenon of multiple females associated with a single male labeled “husband-sharing.” Making the males the active parties (they “share” the female, as if she were a six-pack of beer) may reduce the likelihood of noticing what the females do, of seeing things from their point of view.
What, then, is the lesson from so-called infidelity in animals? The naturalistic fallacy holds that what is natural is good, but what is natural can’t be inherently “good” any more than it can be inherently amusing, inherently painful or more likely to keep your hair shiny. That some animals eat their young should no more suggest an ethic of infanticide than the fact that some animals are yellow should suggest a fashion trend. And using animal behavior to further a social agenda--whether by claiming that cheating is justifiable because it occurs in wrens or by arguing that it is clearly a debasing act that occurs only in lower organisms--is doomed to fail.
The fact that a male blackbird did not sire some of the chicks in his nest is fascinating for what it tells us about evolution, about variation, about what benefits birds in different environmental circumstances. But it says nothing about appropriate behavior in a marriage.
