The Myth of Monogamy: Fidelity and Infidelity in Animals and People by David P. Barash; Judith Eve Lipton Page A
Authors: David P. Barash; Judith Eve Lipton
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(Human beings, too, grow more colorful as they get older, and it is at least possible--if unlikely--that white hair has been selected as a similar symbol of status or, at least, of the ability to survive.)
It seems that the key dimension in these cases is female choice; since males of most species are unlikely to refuse a quick and easy EPC, the deciding vote as to who succeeds and who fails is generally cast by the females, based on whom they find most attractive. But the secondary sexual characteristics of males not only dictate their attractiveness to females, they also influence--and are influenced by--dominance relationships among males. And so, the two factors--dominance relationships and degree of secondary sexual traits--are confounded when it comes to determining which males obtain EPCs. Among cattle egrets, for example, the dominance standing among males has implications for who gets to have EPCs with whose mate. Dominant males have EPCs with the wives of subordinates but not vice versa. (This pattern is of course not unknown among Homo sapiens, too.)
On the other hand, one thing about biology--as compared with, say, chemistry or physics--is that there are lots of exceptions. This applies to the general correlation between male secondary sexual traits and reproductive success no less than to other generalizations (such as "animals eat plants but not vice versa," "only mammals are warm blooded," or "females are smaller than males"). There are, after all, insectivorous plants; it appears that dinosaurs were warm blooded, and among some species--such as jacanas, described earlier--females are larger than males. Similarly, male secondary sexual traits don't always correlate with reproductive success; that is, sexy males don't always get more EPCs, or--more important--they don't always get more EPFs (extra-pair fertilizations). Are these, like the examples of sex-role reversal described earlier, cases of exceptions "proving" the rule? It's too early to say.
It is clear that even in ostensibly monogamous species, males seek--and often obtain--EPCs. It is also clear that they do so at the expense of other males, namely, the ones "married" to those females who succumb to their charms. For an EPC-seeking male, the best arrangement is to father children with females who are already mated. In such cases (assuming the female is able to deceive her in-pair mate as to her infidelity and, thus, his nonpaternity), the female will gain paternal assistance from the cuckolded male, making it more likely that any offspring thereby conceived will be sue-
undermining the myth: males 29
cessful. At the same time, the extra-pair male receives this additional payoff: Since any resulting offspring will be reared by someone else, there is no additional parental effort required. Not only that but--at least in the case of birds--by having multiple sexual partners, extra-pair males literally succeed in placing their eggs in more than one basket. On the other hand, an EPC with an already-mated female is almost always riskier than one with an unmated female, since the outraged husband may find out and drive off an interloping male, possibly injuring him.
For the potential cuckold, therefore, an important option is to guard "his" female from gallivanting males, thereby possibly preventing them from achieving their aims.
(All this assumes, by the way, that the result of a successful EPC is that a mated female ends up bearing offspring sired by one or more extra-pair males and that, therefore, the in-pair male is the one who is victimized. But occasionally the in-pair female can be the loser: In one recorded instance, a mated male zebra finch succeeded in inseminating an unmated female, who then laid an egg in that male's nest. The result was one of the few documented cases in which, as a result of an EPC, the cuckolded party was a female --in whose nest the egg was laid--rather than a male. Most of the time, however, cuckolds are male, and for
It seems that the key dimension in these cases is female choice; since males of most species are unlikely to refuse a quick and easy EPC, the deciding vote as to who succeeds and who fails is generally cast by the females, based on whom they find most attractive. But the secondary sexual characteristics of males not only dictate their attractiveness to females, they also influence--and are influenced by--dominance relationships among males. And so, the two factors--dominance relationships and degree of secondary sexual traits--are confounded when it comes to determining which males obtain EPCs. Among cattle egrets, for example, the dominance standing among males has implications for who gets to have EPCs with whose mate. Dominant males have EPCs with the wives of subordinates but not vice versa. (This pattern is of course not unknown among Homo sapiens, too.)
On the other hand, one thing about biology--as compared with, say, chemistry or physics--is that there are lots of exceptions. This applies to the general correlation between male secondary sexual traits and reproductive success no less than to other generalizations (such as "animals eat plants but not vice versa," "only mammals are warm blooded," or "females are smaller than males"). There are, after all, insectivorous plants; it appears that dinosaurs were warm blooded, and among some species--such as jacanas, described earlier--females are larger than males. Similarly, male secondary sexual traits don't always correlate with reproductive success; that is, sexy males don't always get more EPCs, or--more important--they don't always get more EPFs (extra-pair fertilizations). Are these, like the examples of sex-role reversal described earlier, cases of exceptions "proving" the rule? It's too early to say.
It is clear that even in ostensibly monogamous species, males seek--and often obtain--EPCs. It is also clear that they do so at the expense of other males, namely, the ones "married" to those females who succumb to their charms. For an EPC-seeking male, the best arrangement is to father children with females who are already mated. In such cases (assuming the female is able to deceive her in-pair mate as to her infidelity and, thus, his nonpaternity), the female will gain paternal assistance from the cuckolded male, making it more likely that any offspring thereby conceived will be sue-
undermining the myth: males 29
cessful. At the same time, the extra-pair male receives this additional payoff: Since any resulting offspring will be reared by someone else, there is no additional parental effort required. Not only that but--at least in the case of birds--by having multiple sexual partners, extra-pair males literally succeed in placing their eggs in more than one basket. On the other hand, an EPC with an already-mated female is almost always riskier than one with an unmated female, since the outraged husband may find out and drive off an interloping male, possibly injuring him.
For the potential cuckold, therefore, an important option is to guard "his" female from gallivanting males, thereby possibly preventing them from achieving their aims.
(All this assumes, by the way, that the result of a successful EPC is that a mated female ends up bearing offspring sired by one or more extra-pair males and that, therefore, the in-pair male is the one who is victimized. But occasionally the in-pair female can be the loser: In one recorded instance, a mated male zebra finch succeeded in inseminating an unmated female, who then laid an egg in that male's nest. The result was one of the few documented cases in which, as a result of an EPC, the cuckolded party was a female --in whose nest the egg was laid--rather than a male. Most of the time, however, cuckolds are male, and for
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