The Myth of Monogamy: Fidelity and Infidelity in Animals and People (19 page)

Possibilities abound. For example, by copulating frequently, a female could increase her mate's confidence that he is the father, making him less likely to desert, more likely to help, and perhaps also less inclined to seek EPCs. Such enhanced confidence might or might not be justified: Frequent copulation probably does suggest a higher probability of paternity, but it isn't beyond the capacities of many animals to deceive their mates as to likely paternity in order to keep the male nearby and also more inclined to help take care of the kids.

Finally, an oft-copulating female might not simply be acting on her sexual motivation; she may also be
signaling
that she is sexually inclined. Throughout the animal world, such inclinations are generally at least somewhat correlated with ovulation and could therefore influence her mate to stick around and mate-guard ... since EPCs loom as the alternative.

"TTt is a truth, universally acknowledged," writes Jane Austen in the
I
famous opening sentence of
Pride and Prejudice,
"that a single man, in
JL
possession of a good fortune, must be in want of a wife." She goes on:

However little known the feelings or views of such a man may be on his first entering a neighborhood, this truth is so well fixed in the minds of surrounding families that he is considered the rightful property of some one or other of their daughters.

Less universally acknowledged is the appeal of material resources to those daughters themselves, an appeal that may be so great that a man "in possession of a good fortune" may obtain copulations even if he is not single, or not "in want of a wife." In short, females may be inclined toward EPCs even if they are not prospecting for genes--if the material rewards are sufficient.

Red-billed gulls, studied off the coast of New Zealand, show a common pattern: Females who are well fed during courtship resist all EPC attempts, and they also remate with their partner the following year; on the other hand, females who had been poorly provisioned are especially likely to

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the myth of monogamy

divorce in the future and are more likely to submit to EPCs--and even to solicit them. We have already reviewed a similar pattern among ospreys, another species in which males are expected to provide substantial calories and in which females engage in EPCs if their mates slack off.

It is at least possible that among species such as ospreys and red-billed gulls, which generally form long-term pair-bonds and which invest heavily in producing chicks and then caring for them, males are better off taking good care of their wives rather than spending their time and energy gallivanting. After all, in such species, males that switch partners end up with fewer successful offspring than do those who remain faithful and affiliated. In such cases, as red-billed gull expert J. A. Mills concludes, "the attentive prosper." Marital virtue--in this case, bringing home the bird equivalent of "the bacon"--may be its own reward, or rather, it can lead to higher reproductive rewards. Ditto for female fidelity, in all likelihood, but with the added proviso that if your male isn't a good provider, you might be better off mating with someone else.

There is a hard-hearted but deep-seated logic in females exchanging sex for resources and, if possible (or necessary), looking elsewhere for sex in the event that adequate resources aren't forthcoming from one's own mate. Among human beings, there is a long cross-cultural history of women being wooed by display of resources and being disaffected by material want. There is also a long cross-cultural history of men, whether married or not, using money to obtain sex from women, who also may or may not be married.

Moreover, even if prostitution isn't the world's oldest profession, it is without doubt one of the most widespread. And there is a difference only in degree between the prostitute who offers sexual services in return for a fee and the mistress who makes a similar exchange with a man who may be married but who has sufficient resources to provide her with various material benefits: an apartment, fancy clothing, jewelry, luxurious meals and vacations, and so forth. To be sure, the man "keeping" a mistress or visiting a prostitute is not attempting to reproduce, nor--in virtually all cases-- is the woman. But in trading sex--often EPCs--for resources, people are almost certainly responding to an ancient connection, one that recent research has made increasingly evident.

The animal world is similarly filled with examples of females providing sexual access to themselves in exchange for resources controlled by males. Among the purple-throated Carib hummingbirds, males defend territories containing as many flowering trees of a particular, highly valued species as possible, aggressively chasing away other males. Interestingly, they also attack trespassing females ... except those that solicit copulations. The technical article describing this system is aptly titled "Prostitution Behavior in a Tropical Hummingbird."

undermining the myth: females (other considerations)
93

Another example comes from an odd little bird--the orange-rumped honeyguide--that lives in Nepal and loves to eat beeswax. Beehives, not surprisingly, are highly valued and are defended energetically by male hon-eyguides. To obtain the treasured beeswax, a female must first copulate with the proprietor male. In the world of orange-rumped honeyguides, "those that have, get," and those that don't, don't. Indeed, only hive-owning males do any mating, and one particularly "wealthy" male was observed to copulate 46 times with at least 18 different females during one breeding season.

In other cases, the concept of male as "provider" is taken even more literally, to the extent that the successful male may appear less enviable, at least to the human observer. Thus, certain spider species practice female sexual cannibalism, by which females profit directly from multiple copulations if only because they get to eat their numerous sexual partners. Although there is little obvious benefit from consuming just one male (especially since, in such species, the males tend to be much smaller than their voracious mates), multiple matings offer females the alluring prospect of a multicourse meal. It is conceivable that in such cases, the material benefit of munching on males--even more than mating with them--is what drives females to copulate as often as they do.

The insect world is especially rich in peculiar patterns of this sort, whereby females gain material benefits in unexpected ways. For example, in a species of moth, adults and eggs achieve protection from their predators via certain chemicals known as pyrrolidine alkaloids (PAs). The moths cannot synthesize PAs; they have to obtain them from plants they eat or-- more efficiently--from a male who has eaten these plants. Males secrete PAs into their spermatophores, large blobs of proteinaceous goo that are transferred to the female during mating and are consumed by her, whereupon they protect her and her eggs. Male moths attract females by use of specialized chemicals, pheromones, and the most effective pheromones--the ones most likely to turn on a female moth--are those containing large doses

"o one ever considered chimps monogamous. They have long been

known, in fact, for the diverse, inscrutable, amorphous complexity

-A*.
^| of their sex lives. Alternatively, one might say that chimpanzee sexual arrangements were notorious for their simplicity: their
lack
of structure. But the former interpretation--complexity--is more likely accurate. Some tantalizing new discoveries about the sex lives of chimps have begun shedding light not only on
Pan troglodytes
themselves but also on yet another reason why females may engage in EPCs: recruiting lovers to provide enhanced care and protection of their offspring.

of PAs.

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the myth of monogamy

Female chimpanzees in heat will sometimes associate preferentially with one male, with the duo occasionally even isolating themselves from other troop members for several days to a few weeks. More often, a dominant male may monopolize (or attempt to monopolize) sexual access to a given female, especially when her anogenital swelling indicates that she is at peak fertility. Most commonly of all, females will copulate with many different males in their troop, although even in this case they seem especially prone to being inseminated by the most dominant adult male, since they are most likely to have sex with him when they are ovulating. At the same time, however, chimpanzees were at least thought to restrict their promiscuity (is "restricted promiscuity" an oxymoron?) to their own social group. No more.

It had long been assumed that the reason adolescent female chimps disperse from their social group is to avoid inbreeding. It may still be. But now it is also clear that females are not limited to the troop in which they reside; rather, they can--and do--mate with other males on the sly.

It is now apparent--once again, as a result of modern DNA technology--that females actively seek and obtain mating partners from outside their social unit. (Not quite an example of EPCs; we might call them EGCs--extra-group copulations.) It had long been known, from field observations, that females occasionally leave their troops for periods of a day or more, although no one knew why.

Recently, however, a study of chimps in the Tai forest, Cote dTvoire, found the answer. Females actively seek out mating partners from adjoining groups. In 13 cases, mother-infant pairs were analyzed for their DNA content and the results compared with DNA profiles obtained for in-group males. The results were startling: In 7 of these 13 cases, all the in-group males could be excluded as possible fathers! So, the baby chimps must have been fathered by males outside the mothers' group. Interestingly, all 7 of these females were known to have left their troops during their estrous period, precisely when the infants in question would have been conceived. It is also interesting that such absences are brief--in 4 cases, only one to two days-- and, moreover, matings with nongroup males must be exceedingly furtive: During 17 years of continuous observations, the sharp-eyed researchers saw nary a one! (Without the DNA analysis, we would have had no way of knowing about this furtive aspect of the love lives of female chimps.)

The researchers suggest that this behavior by females allows them to choose from a wider variety of potential mating partners while still retaining the resources and social support of their in-group males. Another major possibility: They gain toleration of their young when different troops interact. Males may well say to themselves, in effect: "I remember this female, an old flame from several months ago. So maybe, just maybe, this cute little baby is my kid!"

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Paternal perceptions of this sort, whether accurate or not, may turn out to be especially important for the survival of young chimps. An ethically troubling discovery--deriving initially from the pioneering research of pri-matologist Sarah Hrdy--has been that many animals practice infanticide. In brief, the pattern is as follows: Among polygynous species, when the harem-keeping male is eventually deposed, the newly ascendant male not uncommonly embarks on a grisly policy of killing the nursing infants. Although despicable by human moral standards, such behavior makes "good" evolutionary sense, since after their youngsters are eliminated, nursing mothers quickly resume ovulating, whereupon they are likely to mate with the new harem-keeper ... despite the fact that he murdered their offspring. Insofar as the unfortunate infants were sired by the preceding male, their fate is of no biological concern to the newly ascendant infanticidal male. He is interested in his own progeny, not someone else's.

Female langur monkeys have even evolved an interesting counterstrategy. If a female langur is in the late stages of pregnancy when a male takeover occurs, she may undergo a "pseudo-estrus," developing swollen genitals and a sexual appetite for the new harem-keeper. Then, when her offspring is born, the adult male is more likely to act paternal than infanticidal.

Among many species, including chimpanzees and numerous other primates, the danger of infanticide is not limited to the aftermath of male takeovers. It is ever-present whenever two groups meet. However, as Sarah Hrdy has pointed out, given that even hard-hearted adult males are concerned about their own progeny, it may be that by copulating with more than one male, females introduce a degree of strategic uncertainty (or even erroneous confidence) as to whether a male who has enjoyed a female's sexual favors may accordingly have fathered her offspring. If so, then EPCs might serve as a kind of infanticide insurance, a means whereby females purchase a degree of immunity for their offspring.