The Myth of Monogamy: Fidelity and Infidelity in Animals and People by David P. Barash; Judith Eve Lipton Page B
Authors: David P. Barash; Judith Eve Lipton
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good reason: Among all species with internal fertilization--including birds, mammals, and reptiles--a female "knows" that any offspring emerging from her body is genetically hers, whereas a male has to take his mate's word for it, unless he is an especially assiduous mate-guarder.)
Let's take a brief excursion to a cattle pasture, almost anywhere in the world. One common occupant--far more numerous than the cows--is a tiny insect, the yellow dungfly. Male dungflies gather around cowpatties, especially the fresh ones, where they search for females who are about to lay their eggs in the warm, gooey interiors. Interestingly, these arriving females have nearly always copulated before arriving at the egg-deposition sites. Therefore, they already contain enough sperm in their genital storage organs to fertilize all their eggs. Yet before ovipositing, they copulate once again with at least one waiting male. Why?
The answer seems to be that among dungflies, the last male to mate guards "his" female until she is finished laying her eggs. Having such a protector greatly reduces the harassment that a female would otherwise receive from other males. This isn't a bad deal for males, either, since they experience a "last male advantage": The last male to mate fertilizes more than 80 percent of a female's eggs. Guarding takes about a quarter of an hour, which is probably a good trade-off.
Guarding doesn't always work, though. If another male dungfly, much larger than the guarder, attacks the pair, he may succeed in copulating yet again with the female, after which he proceeds to stand guard himself.
30 the myth of monogamy
Mate-guarding is very widespread. It is even possible that the well-known tendencies for animals of many different species to establish and defend territories is really a consequence of males guarding the sexual rights to their mates by defending a region surrounding them. In a sense, mate-guarding is one of the clearest animal (or human) manifestations of sexual jealousy, and it is sometimes quite overt, with the male shadowing every movement of his mate. Such "togetherness" is almost certainly not a simple--or even complex!--matter of love or loneliness, since it is nearly always limited to precise times when the female in question is fertile. Male bank swallows, for example, closely follow their mates, flying along nearby whenever they venture from their nests; such devoted attention quickly terminates, however, when the females are no longer fertile.
Mate-guarding is also a common male strategy among mammals, especially when the female is in estrus. The goal, once again, is evidently to thwart EPCs. Mate-guarding is also widespread, almost universal, among that mammalian species known as Homo sapiens: A now-classic anthropological review recorded that only 4 out of 849 human societies did not show some signs of mate-guarding, whereby men keep close tabs on their mates. In some societies, husbands even time their wives' absences while they are in the bushes urinating or defecating. Such concern may not be ill founded; one piece of British research found that the less time a woman spent with her primary mate (husband or identified main sexual partner), the more likely she was to have copulated with someone else.
We used to think that the close association of male and female, especially in a monogamous species, was simply a manifestation of their close pairbond, as well as perhaps a way of further enhancing their relationship. Here is a description of courtship among European blackbirds, from a classic 1933 account by ornithologist E. Selous:
The male bird follows her all about, hopping where she hops, prying where she pries, and seeming to make a point of doing all she
does except actually collect material for the nest____Then, the one
laden, the other empty-billed, they both fly back in just the same way, and the cock will sit again ... for the cock is as busy in escorting and observing the hen as she is in
Let's take a brief excursion to a cattle pasture, almost anywhere in the world. One common occupant--far more numerous than the cows--is a tiny insect, the yellow dungfly. Male dungflies gather around cowpatties, especially the fresh ones, where they search for females who are about to lay their eggs in the warm, gooey interiors. Interestingly, these arriving females have nearly always copulated before arriving at the egg-deposition sites. Therefore, they already contain enough sperm in their genital storage organs to fertilize all their eggs. Yet before ovipositing, they copulate once again with at least one waiting male. Why?
The answer seems to be that among dungflies, the last male to mate guards "his" female until she is finished laying her eggs. Having such a protector greatly reduces the harassment that a female would otherwise receive from other males. This isn't a bad deal for males, either, since they experience a "last male advantage": The last male to mate fertilizes more than 80 percent of a female's eggs. Guarding takes about a quarter of an hour, which is probably a good trade-off.
Guarding doesn't always work, though. If another male dungfly, much larger than the guarder, attacks the pair, he may succeed in copulating yet again with the female, after which he proceeds to stand guard himself.
30 the myth of monogamy
Mate-guarding is very widespread. It is even possible that the well-known tendencies for animals of many different species to establish and defend territories is really a consequence of males guarding the sexual rights to their mates by defending a region surrounding them. In a sense, mate-guarding is one of the clearest animal (or human) manifestations of sexual jealousy, and it is sometimes quite overt, with the male shadowing every movement of his mate. Such "togetherness" is almost certainly not a simple--or even complex!--matter of love or loneliness, since it is nearly always limited to precise times when the female in question is fertile. Male bank swallows, for example, closely follow their mates, flying along nearby whenever they venture from their nests; such devoted attention quickly terminates, however, when the females are no longer fertile.
Mate-guarding is also a common male strategy among mammals, especially when the female is in estrus. The goal, once again, is evidently to thwart EPCs. Mate-guarding is also widespread, almost universal, among that mammalian species known as Homo sapiens: A now-classic anthropological review recorded that only 4 out of 849 human societies did not show some signs of mate-guarding, whereby men keep close tabs on their mates. In some societies, husbands even time their wives' absences while they are in the bushes urinating or defecating. Such concern may not be ill founded; one piece of British research found that the less time a woman spent with her primary mate (husband or identified main sexual partner), the more likely she was to have copulated with someone else.
We used to think that the close association of male and female, especially in a monogamous species, was simply a manifestation of their close pairbond, as well as perhaps a way of further enhancing their relationship. Here is a description of courtship among European blackbirds, from a classic 1933 account by ornithologist E. Selous:
The male bird follows her all about, hopping where she hops, prying where she pries, and seeming to make a point of doing all she
does except actually collect material for the nest____Then, the one
laden, the other empty-billed, they both fly back in just the same way, and the cock will sit again ... for the cock is as busy in escorting and observing the hen as she is in
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