Evolution's Rainbow. Joan Roughgarden

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СКАЧАТЬ harem to obtain matings and yet burdened the males within their harem with the job of raising the young. The investigators, themselves male, were outraged, asserting that male jacanas were being “cuckolded” in spite of contributing so much parental care. One investigator stated, “It’s about as bad as it can be for these guys.”⁸

      The converse probably wouldn’t have provoked such outrage. A female in a harem controlled by a male might raise a chick fathered by that male and placed there by a female from a neighboring harem. We could imagine many reasons for such an adoption. The female might find it advantageous to raise the chick in return for the controlling male’s provisioning and protection of the young she has mothered herself. Similarly, a male jacana might find it advantageous to raise a chick mothered by the controlling female in return for the controlling female’s provisioning and protection of the young he has fathered himself. Thus, sex-role reversal implies that the double standard also reverses. This idea takes some getting used to.

      Other birds showing sex-role reversal include two shore birds, Wilson’s phalarope and the spotted sandpiper.⁹ Apparently, no mammals exhibit sex-role reversal, presumably because of the very high parental investment by mammalian females. In addition to the egg, a mammalian female supplies milk to the embryo and carries the young to term, either in a placenta or a pouch. For a mammalian male, this act is hard to follow. To exceed this already high parental investment by a female, a male would require a social system allowing him to care for his offspring well beyond the age of weaning, as may be approached in humans.

      The evolution of the mammalian placenta and pouch is usually presented as a physiological advance, an adaptation for nurturing embryonic development in a climate that has cooled globally since the time of dinosaurs. Alternatively, the evolutionary force behind the placenta and pouch may have been for females to assume control of their offspring. A side effect is that males then acquire an incentive to control females.

      5

      Two-Gender Families

      Let’s move on now to species with two genders that don’t change sex, do not have intersexual body parts, and aren’t sex-role reversed. Are such animals “normal”? Have we come at last to the familiar gender roles performed by ordinary bodies, as depicted on nature shows? Or are nature shows perhaps not telling the whole story? What goes on in two-gender animal families, and how are such families organized?

      Many of us were raised to admire the nuclear family as a norm and were taught that single-parent families, families of same-sex couples, or communes were second-best alternatives or, even worse, wrong. Yet the meaning of a human family is in flux. In the United States, public attention has focused on the problem of how to define “family” as a result of a recent Supreme Court case about the rights of grandparents to visit grandchildren despite parental objection. The thirty-million-member American Association of Retired People (AARP) states that grandparents are the primary caretakers of 1.4 million children because many nuclear families have dissolved.¹

      The American Center for Law and Justice, which represents the Christian right, claims that “the traditional family, consisting of married parents and their children” is the building block of society. A leader of the Nation of Islam similarly declares, “Whenever . . . 50% of those who marry get divorced within the first three years, these are signs of the decline of a civilization.”²

      Meanwhile, the Lambda Legal Defense and Education Fund, a gay rights organization, argues that neither side, grandparents or parents, sufficiently protects children being reared in nontraditional families, affirming the primary importance of “the quality and security of the relationship between individual children and adults rather than blood ties or labels.”³ Indeed, in June 2002, the California Supreme Court ruled unanimously that a man who cared for a six-year-old boy could be considered the boy’s parent, even though the man was not the boy’s biological father and was never married to the boy’s mother. The man was given custody of the child over the mother’s objections, showing that “parenthood could be achieved through love and responsible conduct.”⁴

      With so much controversy about the meaning of family and parenthood, asking how animals raise their young may be helpful. What is an animal family? Does any family organization emerge as a particularly efficient way to raise young? And does biology support the belief that the nuclear family should have a privileged status in our society?

      SEX AND POWER

      Oh, I wish the simplest of animal families were a blissfully pair-bonded male and female. Alas, males and females negotiate over power in even the most elementary of animal families. Feminist writings call attention to a power differential between the sexes: “The image of the cage helps convey . . . the nature of oppression. ‘Why can’t I go to the park; you let Jimmy go!’ ‘Because it’s not safe for girls.’ “⁵ Well, how safe is it outside the cage? Why does a cage exist at all? If we look at squirrels, we can see what biologists call “mate guarding,” a male caging a female.

      The Idaho ground squirrel (Spermophilus brunneus) lives in populations of one hundred to three hundred individuals in short-grass meadows.⁶ The squirrels hibernate in burrows most of the year, only becoming active from late March to early August. The males wake up from hibernation about two weeks before the females. Females become sexually active for about three hours in the afternoon on the first day after hibernation. Three hours on this one day is all the family life a squirrel has.

      

      A successful date for a male squirrel means walking behind a female while sniffing and licking her genitals, going with her into a burrow, mating there for five minutes, and then reemerging. As a sign of successful mating, the female acquires a “sperm plug” that can be seen by a human observer and probably by other squirrels as well. The male then stays within one meter of her and keeps her in a small area by “herding.” About every forty minutes, he follows her back into the burrow, where they mate again. She acquires a fresh sperm plug, and he turns around to block the entrance with his body. The male rebuffs an average of four other males who try to mate with the female. If a male is displaced, he is likely to take about an hour and twenty minutes to locate another female, and she is usually guarded by some other male.

      A litter typically consists of five pups. If the female has been guarded by only one male for these three hours, then the whole litter is sired by him. If more than one male has guarded the female, paternity analysis shows that her litter is sired mostly by the male who was the last to guard her or by the male who guarded her the longest.

      Thus the family life of the Idaho ground squirrel consists of three hours per year. The Idaho ground squirrel family is solely a unit for reproduction. The male doesn’t hang around and help raise the young. The male is said to guard the female to protect his “investment” of sperm by making sure that his female doesn’t mess around. He doesn’t mess around himself because if he stopped guarding he would lose his investment, and in any case finding another female is nearly impossible.

      A close relative, Belding’s ground squirrel (Spermophilus beldingi) of the midwestern United States, does not mate-guard. In this species, twenty-five minutes are all a male needs to locate and initiate courtship with another female. Female Belding’s squirrels typically mate with three to five males. The female’s first mate sires most of the litter, followed by the second mate, then the third mate, and so on, in contrast to the Idaho squirrel, where the last mate gets most of the sires. A Belding’s male doesn’t waste time guarding a female because his investment of sperm is secure—as the first mate, he’s already guaranteed siring most of the young. Instead, these males hurry to find more females to mate with, and with so many nearby, why not?

      A cage, then, is not biologically universal. These two closely related species of squirrels have completely different power relationships between СКАЧАТЬ