Female Sabotage

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Soon after Charles Darwin published his theory of Natural Selection, he was faced with a puzzle. If natural selection is "survival of the fittest," then why do some males have traits that detract from their survival? For instance, the peacock grows a colorful, cumbersome tail, that not only attracts predators, but makes it hard for him to escape those predators. Similarly the buck grows enormous antlers, which are heavy to carry, and which can easily become caught in branches, interfering with effective escape from pursuing hunters.

Darwin knew, of course, that "survival of the fittest" is an oversimplification. An equally important part of the struggle of life is to produce offspring, and that the problem is not simply survival, but also reproduction. In this case, the question becomes, "Why would a female burden her sons with dangerous traits by mating with a similarly burdened male?”

Noting that the males with burdensome traits are almost entirely those in polygamous species, where a minority of males generally mate with many females, Darwin had an insight. He realized that if females found these male burdens more "attractive", and if that attractiveness resulted in more matings by burdened males, then the increase in matings of a few sons might offset the death of many other sons as a result of the burden. In effect, if the success of the surviving males produced enough offspring to cover more than the loss of potential offspring from their lost brothers, then the female who mated with a burdened male had chosen correctly.

In 1996, however, Joe Abraham presented a decidedly feminist re-interpretation of the problem. In polygamous species, males generally contribute nothing to the nurturing of offspring, but are nevertheless consuming resources. In effect, after mating, males become competitors with females and young. This gives females a reason to sabotage males, and mating gives them an opportunity. By exclusively mating with males carrying burdens that will cost them an increased mortality rate, then as males die, more food and other resources will remain for females and their young.

In addition, just as a given amount of land can only produce so much grazing, and a limited amount of grazing can only support a limited number of grazing animals, so a given number of grazing animals can only sustain a limited number predators. These sorts of limitations apply to all living things, and are known as the carrying capacity of a certain physical area. If males' burdens also distract local predators, then males are effectively shifting predation away from females and their young. In such a case, the females and young will gain an added benefit from decreased predation, and enjoy even higher rates of survivability.

Abraham's explanation reunites the major split in sexual selection-- intrasexual selection (male combat) and intersexual selection (female choice)-- together under one rubric. Under female sabotage, the increase in resources becomes the critical factor, and the cause of increased male mortality is secondary. But perhaps the most attractive aspect of Abraham's explanation is that it can easily work with any of the many current theories of sexual selection. An increase in resources and a decrease in predation for females and their young is an inevitable result of increased male mortality, regardless of what mechanism drives females to mate with males carrying burdensome traits.