The Myth of Monogamy: Fidelity and Infidelity in Animals and People by David P. Barash; Judith Eve Lipton
Authors: David P. Barash; Judith Eve Lipton
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young adults serve as "helpers at the nest," assisting others to reproduce rather than rearing their own offspring. With our recent appreciation of EPCs, a new wrinkle has emerged in interpreting such seemingly altruistic behavior. Even "helper" males may actually be helping themselves... to occasional sex: with the breeding female. So-called cooperative breeding may therefore involve less altruism than had recently been thought, since, in at least some cases, what looks like altruistic baby-sitting is actually full-fledged parental investment, provided to offspring of the helpers themselves, some of whom were conceived via circumspect EPCs.
And yet, confidence of relatedness doesn't explain all aspects of parenting. For example, an experiment looked at the paternal behavior of male common gobies; these are small marine fish, the males of which guard eggs left them by a female. The goal of the experiment was to assess whether male common gobies treat their offspring differently depending on whether they had spawned alone (with a female but no other male) or with a second male present, in which case there was at least a chance that some of the eggs and fry were fathered by the interloper. It turned out that it didn't matter whether a second male had been present.
The gobies are not alone. It is not invariant that paternal care varies with confidence of paternity; there are some notable exceptions, not only among fish but among birds as well. What are we to make of these exceptions? (Make no mistake: Exceptions they are.) If they were the rule, then we'd have to reassess some basic evolutionary and genetic principles. As exceptions, they provide us with the opportunity to fine-tune our predictions.
In the case of occasional paternal care by nonpaternal animals, other factors appear to be at work. For example, if EPCs don't usually occur in a given species, then, lacking the context, there would be little or no evolutionary pressure selecting for a male's ability to detect his likely nonpaternity and to react accordingly. Natural selection can only generate a response if, in the past, situations have arisen that cause individuals responding in one way to be more successful than individuals responding in other ways. By the same token, we lack the ability to hear ultra-high-frequency sounds because such sounds have not been part of the relevant landscape in which our ancestors evolved; the same is not true of certain moths, however, which
48 the myth of monogamy
have evolved the ability to hear and respond to the ultra-high-frequency sounds emitted by a highly relevant part of their environment: hunting bats.
It is also possible that, in some species, males simply lack the ability to detect eggs or offspring not their own, even though it might be to their benefit if they could. Or maybe in certain cases the payoff that comes with discriminating "my genes" from "someone else's" is substantially reduced by certain disadvantages, such as the costs of occasionally erring and discriminating against one's own offspring after all. Nonetheless, there is little doubt that incursions--especially by a male into the territory of a monogamous breeding couple--are not appreciated . . . especially by the resident male.
In the mid-1970s, David conducted this experiment in Mount Rainier National Park: He attached a model of a male mountain bluebird near a female and her nest, so that when the female's actual mate returned, he discovered his female in close association with this apparent stranger. The male behaved aggressively toward the model and also toward his own mate, in one case driving her away; she was eventually replaced with another female, with whom he successfully reared a brood. This little study became somewhat controversial, with researchers debating, among other things, the propriety of biologists acting as Iago and inducing violent sexual jealousy on the part of their subjects! In any event, there have since been numerous
And yet, confidence of relatedness doesn't explain all aspects of parenting. For example, an experiment looked at the paternal behavior of male common gobies; these are small marine fish, the males of which guard eggs left them by a female. The goal of the experiment was to assess whether male common gobies treat their offspring differently depending on whether they had spawned alone (with a female but no other male) or with a second male present, in which case there was at least a chance that some of the eggs and fry were fathered by the interloper. It turned out that it didn't matter whether a second male had been present.
The gobies are not alone. It is not invariant that paternal care varies with confidence of paternity; there are some notable exceptions, not only among fish but among birds as well. What are we to make of these exceptions? (Make no mistake: Exceptions they are.) If they were the rule, then we'd have to reassess some basic evolutionary and genetic principles. As exceptions, they provide us with the opportunity to fine-tune our predictions.
In the case of occasional paternal care by nonpaternal animals, other factors appear to be at work. For example, if EPCs don't usually occur in a given species, then, lacking the context, there would be little or no evolutionary pressure selecting for a male's ability to detect his likely nonpaternity and to react accordingly. Natural selection can only generate a response if, in the past, situations have arisen that cause individuals responding in one way to be more successful than individuals responding in other ways. By the same token, we lack the ability to hear ultra-high-frequency sounds because such sounds have not been part of the relevant landscape in which our ancestors evolved; the same is not true of certain moths, however, which
48 the myth of monogamy
have evolved the ability to hear and respond to the ultra-high-frequency sounds emitted by a highly relevant part of their environment: hunting bats.
It is also possible that, in some species, males simply lack the ability to detect eggs or offspring not their own, even though it might be to their benefit if they could. Or maybe in certain cases the payoff that comes with discriminating "my genes" from "someone else's" is substantially reduced by certain disadvantages, such as the costs of occasionally erring and discriminating against one's own offspring after all. Nonetheless, there is little doubt that incursions--especially by a male into the territory of a monogamous breeding couple--are not appreciated . . . especially by the resident male.
In the mid-1970s, David conducted this experiment in Mount Rainier National Park: He attached a model of a male mountain bluebird near a female and her nest, so that when the female's actual mate returned, he discovered his female in close association with this apparent stranger. The male behaved aggressively toward the model and also toward his own mate, in one case driving her away; she was eventually replaced with another female, with whom he successfully reared a brood. This little study became somewhat controversial, with researchers debating, among other things, the propriety of biologists acting as Iago and inducing violent sexual jealousy on the part of their subjects! In any event, there have since been numerous
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