Homo Mysterious: Evolutionary Puzzles of Human Nature (17 page)

We must conclude that even though the route from genotype to sexual orientation is winding and not yet entirely revealed, it unquestionably exists. Given, furthermore, that homosexuality is a cross-cultural universal, with the proportion remaining roughly the same around the globe and throughout human history, we are left with an undeniable evolutionary puzzle. In the pages to come, we will not unravel this puzzle; however, we shall attempt to identify and evaluate some of the key ingredients in what promises to be a very complex situation.

At first glance, homosexuality and altruism seem no more connected than apples and oranges. But of course, apples and oranges aren’t altogether dissimilar (both are fruit). And homosexuality and altruism are similar as well, in that each poses a comparable theoretical dilemma, namely, the fact that alleles promoting either tendency necessarily promise—or threaten—to act against their own propagation. Altruism
means
an action that promotes the success of people other than oneself, and so basic definitional logic says that it should be replaced by alternative genes that promote one’s own success, that is, genes for selfishness. Homosexuality
means
same-sex erotic preference, which also appears logic-bound to diminish the reproductive success of any genes that promote such activity. Like genes for altruism, genes for homosexuality should therefore be replaced by alternative genes, with selfishness succeeding altruism and homosexuality giving way to heterosexuality. But, like altruism, homosexuality does not merely exist; it flourishes in significant numbers.

As it happens, an especially satisfying scientific explanation for altruism has been proposed and is strongly supported by the evidence. It also offers some promise for explaining homosexuality. Known as “inclusive fitness theory” or “kin selection,” it essentially argues that once evolution is seen to operate at the level of genes rather than organisms, the paradox of altruism melts away insofar as individuals are selected to act on behalf of their constituent genes. This is because beneficence toward others, at the level of behaving organisms, although appearing to be altruistic, can constitute unacknowledged selfishness at the level of genes, if “altruists” are actually benefiting identical copies of their own altruism-promoting genes, contained in other bodies. And in fact, humans, like other animals, typically dispense altruism toward genetic relatives—hence the phrase “kin selection.”

This insight, due largely to the genius of theorist William D. Hamilton, has literally revolutionized evolutionary biology in recent decades.
²⁹
It has been used to solve such mysteries as food sharing, alarm calling, and willingness to run risks defending others from predators. It is strongly implied in the “grandmother
hypothesis” for the evolution of menopause, which we have already considered. It also stimulated biologists to look for a possible kin-selected basis for human homosexuality, since the reason food sharing, alarm calling, and predator repelling (in addition to other seemingly altruistic acts) are evolutionary mysteries is that when push comes to shove, they involve foregoing reproductive opportunities for oneself while conveying a compensatory benefit to others. And the answer, of course, is that at the genetic level, those “others” are really “oneself.”
^v

Sharing food, giving alarms, and repelling predators—along with many other forms of social cooperation—were evolutionary conundrums because they translated into reproductive restraint.
^vi
And in fact, the most satisfying application of inclusive fitness theory to a prior evolutionary mystery had to do with explaining the presence of sterile worker castes among social bees, wasps, and ants. It’s a long story, basically revolving around the fact that because of their peculiar genetic architecture, worker bees, wasps, and ants share more genes with the offspring of the queen than they would with their own children, were they to reproduce. Not surprisingly, once kin selection became established within the intellectual repertoire of evolutionary biologists, there ensued a flurry of efforts to ascertain whether it could do for homosexuality what it has done for altruism. How neat it would be if homosexual humans were even a little bit like worker bees, producing on average fewer children than heterosexuals, but compensating genetically via their own inclusive fitness, that is, conveying a reproductive lift to their relatives, and thereby, to their own distinctive alleles.

It seems that the hypothesis was first explicitly proposed by noted evolutionary biologist Edward O. Wilson,
³⁰
who suggested
that because homosexuals were freed from the obligation of investing time and energy on their own reproduction, perhaps they were then able to assist their siblings and other relatives to rear
their
offspring, to the ultimate evolutionary benefit of any homosexuality-promoting genes present in those additional children thereby produced.

Unfortunately, the data suggested otherwise.

For starters, available evidence did not show that homosexuals spent an especially large amount of time helping their relatives, or even interacting with them. Moreover, when homosexuals did provide notable amounts of assistance to others, it did not appear that this helping behavior was especially directed toward genetic relatives.
³¹
Another study, comparing 60 heterosexual with 60 homosexual English men, found “no significant differences between heterosexual and homosexual men in general familial affinity, generous feelings (willingness to provide financial and emotional resources), and benevolent tendencies (such as willingness to baby-sit).”
³²
These results were based on surveys; accordingly, they revealed opinions and attitudes rather than actual behavior. Moreover, they involved modern industrialized societies, which presumably are not especially representative of humanity’s ancestral situations. Nonetheless, it was reasonably concluded that if assisting one’s relatives were a robust feature associated with same-sex preference, it should have been revealed.

Another hypothesis was promptly floated, namely, that since there is some anthropological evidence that homosexual men were more than randomly likely to become priests or shamans, perhaps the additional social prestige conveyed to their heterosexual relatives might have given a reproductive boost to those relatives—and thereby, to any shared genes that predisposed toward homosexuality.
³³
An appealing idea, but once again, sadly lacking in empirical support.

Further discouraging to the kin selection hypothesis is that—especially in modern, Western societies—parents do not generally react with delight when they learn that a child is gay or lesbian, whereas if homosexual children were analogous to the “helpers at the nest” phenomenon among birds, we might expect if not outright enthusiasm at least a consistent level of tolerant acceptance on the part of those older, breeding adults who can expect to
be helped.
^vii
One might also anticipate that if kin selection were involved, homosexuality would be more frequent if there are other siblings to be assisted and vice versa. But in fact, singleton children are no less likely to be homosexual than are those with siblings.

Another problem with attributing homosexuality to kin selection is that it isn’t clear why individuals who enhance their fitness by helping relatives should
also
engage in same-sex erotic and bonding behavior at all. Why aren’t people with an above-average predilection for aiding their relatives also inclined, say, to hop on one leg instead, or to experience olfactory hallucinations, or to talk in tongues? Why should their sexual predisposition be at issue in the first place, and given that it is, why aren’t they inclined to have sex with plants, or to masturbate obsessively? After all, as already noted, same-sex copulations are not in themselves reproductive, and—like any sexual interactions—they also require lots of time and energy, which might otherwise be expended directly on behalf of reproducing relatives or somehow used to obtain other proximate rewards.

But on the other hand, it is possible that—as Mark Twain famously responded to the announcement of his own demise—the death of kin selection as an evolutionary explanation for homosexuality has been greatly exaggerated. Thus, as already noted, the less-than-impressive levels of intrafamily benevolence reported for homosexuals were based on technologized, 20th-century populations, which might not reflect the long period of small-scale, nontechnological hunter-gatherer living in which such tendencies would presumably have evolved. And in fact, some interesting and suggestive research has recently emerged, focusing on male homosexuals among a more traditional population on the island of Samoa.

Known as
fa’afafine
, these individuals do not reproduce. They are, however, fully accepted into Samoan society in general,
and into their kin-based families in particular. Of particular note is that
fa’afafine
are significantly more prone to behave in a positive avuncular manner than are heterosexual uncles. Thus, they are more likely to purchase toys for their nieces and nephews, babysit, contribute money for the children’s education, and generally provide high levels of indulgence and emotional support, in addition to their material assistance. These men are not simply fond of all children; rather, they lavish their attention upon their nieces and nephews (with whom they share, on average, 25% of their genes). This supportive role of
fa’afafine
even exceeds the contributions of heterosexual women as supportive aunts.
³⁴

It has recently been argued, most cogently by anthropologist Sarah Hrdy, that for much of human evolutionary history, child-rearing was not the province of parents (especially mothers) alone; rather, our ancestors engaged in a great deal of “allo-mothering,” whereby nonparents—other genetic relatives in particular—pitched in.
³⁵
It makes sense that such a system would have been derived by
Homo sapiens
, of all primate species the one whose infants are born the most helpless and that require the largest amount of postbirth investment. Insofar as it genuinely does “take a village to rear a child,” no one should be surprised if some of the most engaged assistants turn out to have been the child’s gay relatives.

One effect of modernization has been a reduction in infant mortality and a parallel decrease in average family size, the so-called “demographic transition.” A consequence of this, in turn, might be that with fewer children per family, the industrialized world offers less opportunity for homosexual offspring to convey benefits to their heterosexual siblings, simply because there are fewer of the latter. Add to this the fact that with enhanced mobility, it is increasingly common for children, regardless of their sexual orientation, to leave their nuclear family to attend school and eventually start their own domestic lives. Hence, it is possible that kin selection was involved in the initial evolution of human homosexuality, but with little or no fitness payoff currently detectable, except in traditional societies. It may also be significant, therefore, that unlike the experience of gays and lesbians in much of the industrialized world,
fa’afafine
are fully integrated into Samoan society and are not discriminated against.

The implications are potentially large, and not only for a deeper scientific understanding of how and why homosexuality may have evolved. Thus, if—as may well be the case—homosexuals are only able to display their kin-selected inclinations to assist their heterosexual relatives when homosexuality is tolerated, then what is mal-adaptive is discrimination against homosexuals rather than homosexuality itself. Let’s be more optimistic: If current trends persist and homosexual rights continue their current trajectory toward greater acceptance, this might generate a return not only to a more “natural” human condition but also to a higher inclusive fitness payoff experienced by gays and lesbians as well as—no less—by their relatives.

There is yet another route whereby kin selection could have led to the evolution of homosexuality without requiring that gays and lesbians were doting brothers and sisters, uncles and aunts. If some human ancestors with a same-sex preference merely reproduced less (or not at all), this in itself could have freed up resources for their straight relatives, without necessarily requiring that the former were especially collaborative or directly altruistic to their breeding heterosexual relatives. The argument is similar to one that helps explain the widespread within-family social support for individuals who enter monasteries, nunneries, or the priesthood, substituting homosexual orientation for vows of chastity: Such actions can, in theory, reduce the pressure of scarcity on those left “outside.”

It’s worth emphasizing here that there is currently no evidence for a genetic propensity in favor of taking vows of chastity, whereas there is for homosexual orientation. Also, the “more resources for everyone else” hypothesis has more than a whiff of “group selection” about it, since it posits that by foregoing or diminishing their own reproduction, homosexuals would have conveyed a benefit to the remaining group members. The problem is that these beneficiaries are liable to have included nonrelatives as well as those sharing part of the homosexuals’ genotype. As a result, this hypothesis is vulnerable to selfish exploitation by unrelated group
members who might gain by homosexuals’ reproductive restraint, without having to give up anything.
^viii

But the payoff needn’t have been all or nothing. Freeing up of resources could conceivably have been at least a contributing factor, especially if while diminishing their own reproduction, homosexually inclined individuals were able to enhance the amount of food, living space, adult attention, and so forth that remained “all in the family,” instead of conveying benefit unselectively to everyone in the group.