Evolution's Rainbow. Joan Roughgarden
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taxes the ability of biologists even to describe what’s happening. But the pejorative language biologists have used so far undercuts the attempt to understand cliff swallow society in greater depth.
A DIFFERENT MODEL
Do animals really own anything? The assumption that they do naturalizes human property rights. Because of this assumption, animals can be described as stealing. Biologists are willing to impute ownership to animals, as though animals cared about property as much as people do. A biologist interprets a bird feeding another as wasting food. The bird is said to be incapable, too dumb, to know it’s been duped into giving up hard-earned wages. Yet the same bird is acknowledged to be smart in so many other ways. Why is a bird smart in some ways and dumb in others? Time and again, biologists assume that ownership is well defined, and explain away the failure to be selfish as a limitation of ability, rather than as falsifying the assumption that selfishness is adaptive.
Close genetic relationship among individuals undercuts natural property. Imagine living in a place where you’re closely related to everyone else. In a colony where every individual is related 50 percent to another, do you own half your things or half-own all your things? I don’t know. The clarity of who owns what becomes fuzzy here. Reciprocal and distributed altruism also undercuts natural property. I live in San Francisco among the homeless. I often see people of limited means give to the poor on the streets. Hasn’t someone told them to be selfish? Perhaps they, or their genes, have been there too. What goes around comes around.
Twenty years ago, Sandra Vehrencamp, an evolutionary biologist, introduced the theory that a society’s reproductive skew was connected to what might today be called a “labor market” for cooperative effort within the society. Her focus was on insect colonies with multiple queens. The basic idea is that an animal helps another in exchange for access to reproductive opportunity.35 Some individuals, the privileged, are envisioned to have control of reproductive opportunity, and to pay out some of this opportunity to others who do not have similar access. In return for this paycheck, the underprivileged contribute labor to assist the privileged in their reproduction.
The inequality of reproductive opportunity initially available to different individuals is called a “distributional inequity” by economists. Distributional inequity may reflect territories that vary in exposure to predators or availability of food, water, and a mix of sunny and shady spots. An animal’s political connections may also give it control of resources. Distributional inequity may develop because of inheritance, age, abilities, and luck.
Exchanges of labor for reproduction are especially profitable between relatives, leading to the formation of an extended family wherein the individual who does the breeding is a parent of helpers who remain at the nest. The value to a helper of assisting its parent’s reproduction depends on its genetic relationship to the parent’s offspring. The highest value accrues to offspring who are full brothers or sisters—in this case a helper may not bother with reproducing at all but let the parent do all the work, called kin selection.36
An exchange of help for reproductive opportunity is possible even in the absence of a genetic relationship if the amount of access the helper is paid exceeds the reproductive opportunity the helper would have in the absence of supplying any labor. The reproductive opportunity granted by a privileged individual who employs an underprivileged individual is called a “staying incentive” because this payment leads the underprivileged individual to stay at the nest as a helper instead of leaving to start a new nest. Overall, the theory envisions the animal society as a political economy held together by transactions in the currency of reproductive opportunity.
Extended families form depending on supply and demand within the labor market. If demand for labor is tight—no jobs for youngsters outside of home—then even a small staying incentive will induce them to stay at home and join an extended family. With lots of opportunity outside of the home, even a large staying incentive will not persuade the youngsters from striking out on their own.
According to this thinking, family structure is fluid, changing when opportunities outside the nest vary and when the breeder changes mates (which devalues the genetic paycheck helpers receive for their labor). Great distributional inequity causes reproduction to concentrate in a few individuals by mutual agreement between breeders and helpers, resulting in a high reproductive skew that may amplify the initial inequity. If resources are evenly distributed, almost everyone breeds for himself or herself, and the social system has a low reproductive skew. Sandra Vehrencamp termed these extremes “despotic” and “egalitarian” societies.37
Let’s see how this theory works in an actual case. White-browed scrubwrens of Canberra, Australia, fit the labor-market theory of family dynamics.38 The social groups consist of a breeding female and one or more males (polyandry). In this case, the young males have to decide whether to stay and help mom and dad or to leave and set up a new home. Females build their nest alone and incubate the eggs alone. The males feed the female while she is fertile before the eggs are laid, and while she is incubating the eggs. The males and the females both feed the chicks while they are in the nest and up to eight weeks after they leave the nest. The males fight it out, leading to a dominance hierarchy, with the alpha male on top and the beta male as a subordinate. The question is what the alpha male should allow the beta male to do so that the beta male remains as a subordinate and doesn’t strike out on his own. How does the alpha male hire the beta male as a helper? Four types of multi-male families occur:
1 If the beta male is related to both the alpha male and the female, the beta male helps at the nest and doesn’t father any of the nestlings himself. The alpha male is the sole male parent. Even though the beta male is not the father, the eggs are very worthwhile to him because the eggs are his full siblings. When combined with limited outside opportunity, the beta male finds it reproductively profitable to stay, even without the incentive of sharing in some of the matings. This family has high reproductive skew.
2 If the beta male is related to the female but not the alpha male, the beta male again helps at the nest without mating, even though the eggs are not as valuable to him as they are when both the female and the alpha male are his relatives. Again the alpha male provides no staying incentive. This family too has high reproductive skew.
3 If the beta male is related to the alpha male but not the female, the value of the eggs is even less because the paternity of the eggs is uncertain. About 15 percent of the eggs are fathered by extra-group matings. From the beta male’s perspective, any eggs the alpha male doesn’t father have no value. As a staying incentive, the alpha male allows the beta male to sire about 20 percent of the brood by mating with the female. This family has moderate reproductive skew.
4 If the beta male is not related to either the alpha male or the female, the beta male sires about 50 percent of the brood himself. The alpha male has to share half of all matings, the maximal possible incentive, to keep the beta male as a helper. This family has zero reproductive skew.
Thus the alpha male can be viewed as allotting the beta male access to reproductive opportunity within the family group in whatever amount is necessary to induce him to stay as a helper. In situations 1 and 2, the beta male doesn’t need any staying incentive at all. In situation 3, the alpha male allows the beta male to sire 20 percent of the brood, and in situation 4, to sire half of the brood.
Do you think these families are happy groups of individuals sticking together by mutual consent to fashion productive lives for all? Some biologists are critical, raising three objections.39 The breeder, for one, may find the price of the staying incentives too high and not agree to pay. The helper would then abandon the nest and set forth alone. But the breeder might coerce the helper to stay anyway. However, the breeder might not be able to completely control the helper. The helper would therefore breed surreptitiously to whatever extent he could. This is not a peaceful home, but a family at war.
A second objection concerns whether the net effect of the “helper” is actually to help or to hurt. Does hanging around the nest and bringing in some food now and then yield a net benefit to the breeder? In naked mole-rats, the breeding female aggressively prods “lazy” workers, suggesting a tension between employer and employee.40
A third