Excerpt from Why everyone (else) is a hypocrite. by Robert Kurzban

so, i’d like to talk about birds. Forget humans for a moment, and when i’m done you can worry a lot about whether the kind of explanation i favor doesn’t apply to humans for some reason that you’ll make up but is wrong.

i’ll use birds because the mating pattern of certain bird species illustrates what’s known as the “polygyny threshold model,” which has to do with how female birds choose a mate in certain complex environments. As we’ll see, one result of the model is that it makes it easy to think about how changing the rules of the mating game leave some birds better off and other birds worse off. this is important for thinking about morality.

imagine a bird species in which males set up territories and females choose which male to mate with. High-quality males can defend bigger, richer territories. Low-quality males have to settle for smaller, poorer territories.

suppose i’m a female bird and i’m in the market for a mate. i come to the nesting grounds a little late, and i find that that many of the best males are already taken: other females have already set up housekeeping with the males with the biggest territories. so, i’m faced with a choice. i can either nest with one of the remaining single—but lower quality—males, or i can nest with a male who is already paired, becoming the second female on the patch. is it better to be the only mate of a poorer male or share a better one? the polygyny threshold model focuses attention on the answer to this question: Depending on the details, there will be some monogamously mated pairs and some polygyny. When the payoff to being the second female on a patch is greater than the payoff to being the only mate of an inferior male, there will be polygyny.

now we add the key ingredient: somehow, we make these birds moralistic. they judge certain kinds of behavior “wrong,” and they have the intuition that any bird that does something “wrong” should be punished. this, of course, deters these “wrong” acts. now what happens?

Is morality for the birds?

suppose that our moralistic birds have to make a decision about whether polygyny—two female birds nesting with one male bird—is “wrong,” and suppose that the modules in the bird minds that make this decision are subject to the forces of natural selection. What kind of modules should we expect to find? to figure this out, we have to ask which birds stand to gain reproductive advantage when polygyny is prohibited.

clearly, female birds with the best male mates will do better: their mates won’t be able to acquire secondary females whose offspring would compete for the male’s resources. Enforced monogamy is a strategic win for monogamously mated females. over time, one would expect a moral module regarding monogamy would be very active in females that find themselves in such a situation.

What about the males? Which males gain when polygyny is prohibited? Well, you might think that the low-quality males benefit, since they now might get mates who would otherwise wind up as secondary mates of high-quality males. that’s probably right. so, in some sense there’s a natural alliance between monogamously mated females and low-quality males because they both gain by enforced monogamy. Will they ally against the high-quality males? Maybe. But remember that we’re just talking about the module that morally condemns polygyny.

Which males benefit from all other males being monogamous, even if they themselves are not? that’s nearly all males. From the point of view of any given individual, it’s best to constrain others’ sexual behavior. We’re all in favor of moral rules that prevent others from doing things that harm our own interests. Just look at the seven Deadly sins, a list of all those things we don’t want other people to do, though we might well have an interest in doing them all ourselves. (symmetrically, “virtues” are traits you want other people to possess—altruism, modesty, chastity —even if you yourself are better off avoiding them.) if a high-quality male could prevent some males from polygyny while simultaneously being polygynous himself—having one monogamous mate, and then having illicit but unpunished affairs—that would be the best of all possible worlds in terms of fitness. to the extent that high-quality males can protect themselves from punishment for having extra-pair matings, the rule prohibiting them is less of a problem.

Who stands to lose if monogamy is enforced? single females do, since they’ll be forced to mate with the lower-quality males. Basically, they’ve lost all the advantages of having the choice described in the polygyny threshold model because they can no longer select a potentially better option, becoming the second female on a high-quality male’s patch.

suppose that selection acted on this bird species, and they came to be designed to favor the arrangement that benefited them, even if they couldn’t say why. in the same way that our birds might very much like to have sex without having to understand the relationship between sex and reproduction, they might have preferences for monogamy and polygyny in line with their reproductive interests without knowing the ultimate cause of these preferences.

one can easily imagine what would happen if high-quality males got to make the rules, or, if there were some sort of democracy instituted, how these birds would vote. the point is that in a species in which individuals can constrain others’ behavior with rules, you’d expect evolution to act to cause members of the species to favor rules that serve their reproductive interests even if they don’t know this is why they’re endorsing these rules.

crucially, consider what these birds would say if they could talk. Perhaps the ones in favor of monogamy would talk about things that sound “good,” like love, family, and the “naturalness” of a two-parent nest. they might even refer to a very special magic book where other birds pursing their fitness interests wrote down rules that took on a sort of mystical quality.2

on the other side of the debate, those in favor of polygyny might talk about individual freedoms to do as a free bird will. they might cite moving passages of Declarations and constitutions, and quote famous birds of times past.

it should be clear that any bird social scientists would have a serious problem trying to figure out the true cause of moral intuitions if their only tool was asking other birds to justify their moral stance. Without Darwin, of course, these bird scientists would be in trouble because they wouldn’t know how to think about what the modules designed to generate moral judgments were up to. they would wind up spinning explanations based on introspection, or perhaps a historical riff based on recent events in the local bird population. they would be explaining bird psychology in terms of what it felt like to be a bird, rather than in terms of the logic of design. that probably would lead them down a lot of blind alleys, and leave many, many mysteries.

The scramble for eggs

As the lives of our birds get increasingly complex, selection would cause the modules designed to manipulate others’ sexual behavior to become more sophisticated. to add another wrinkle, suppose there are two kinds of male birds. some males make nice nests and bring back nice worms for the whole family to enjoy. these are investing males, and we’ll call them “dads.”

Another kind of male doesn’t set up house at all. instead of the domestic life, these males offer females a different commodity: good genes. We’ll call the goodgenes guys “cads,” not to prejudge the moral issue, but just for the rhyme with “dads.”3 We assume that cads, on average, have better genes than dads do, but that dads invest more in offspring than cads.

in many species—including many bird species—females choose to mate with males on the basis of how they look because how they look reveals their genetic quality. the reasoning behind this has been discussed elsewhere—most notably perhaps in Darwin’s second great work, Descent of Man—so i won’t rehash it here.4

Who wins and who loses (in terms of evolutionary fitness) with different rules in a population that includes both dads and cads? Which birds want promiscuity? the cads do. they can’t win if the battle is being fought over who brings in the most worms. they only win in a world in which being sexy matters. Without promiscuity, sexy males can’t make the most of what they’ve got.

Dads, however, win if the sexy males can’t be promiscuous. (they also benefit from keeping their females at home, rather than searching for the good-gene cads.) the good females, if they’re unable to get good genes from cads, will go with the dads. if you can’t get the genes, get the worms. so, promiscuity on the part of other birds is bad for dads.

on the female side, mated females are potential losers in a promiscuous world because their mated males might be tempted to stray, potentially diverting precious worms away from her children. so, promiscuity on the part of other birds is bad for mated females. if these birds could vote, then birds in monogamous pairs would cast their ballots for policies—and, in a republic, for the birds who favor policies—that prevent other birds from engaging in practices like sex outside of mateships and anything else that went along with promiscuity. Again, they probably wouldn’t know why they were opposed to these practices. they would be insensitive to arguments about freedom and individual choice. they would probably be “pro-family” and interested in “traditional values” and so on. Further, because they didn’t know why they wanted to constrain other birds’ sexual behavior, they would be forced into contradictory positions. they might be opposed to abortion—the availability of which, by reducing the costs of sex, might well be linked to promiscuity5—and say that their opposition is based on the principle that a new life begins at conception, even though their intuition is really that a female bird who is promiscuous ought to be punished. these birds would be “pro-life,” “pro-family,” and other platitudes, but basically their minds would be designed to prevent other birds from having sex.

oK, enough with the birds, since at this point it should be clear that my point is that humans, just like these hypothetical birds, have moralistic modules designed to favor rules that promote their fitness interests. this might be difficult to believe. But suppose, just for a moment, that opposition to abortion really doesn’t have anything to do with saving the life of the embryo. People’s stance on abortion might then really be a stance based on the output of certain modules designed to limit other people’s promiscuity.6 in this, abortion isn’t all that different from many other ways in which people try to control other people’s sexuality.

Fathers have been sequestering daughters and older women have been curbing younger women’s sexual expression and behavior for millennia. From an evolutionary point of view, sex is fundamental, and if there were going to be some area in which people wanted to set the rules, this would probably be among the first.

organisms are better or worse off, in terms of reproductive success, depending on the rules of the mating game. suppose that humans, like some of our primate relatives, are, potentially at least, somewhat polygynous, with the “best” males getting more than one mate, meaning some males will be left with none. Low-quality males would have a deep, abiding, even crucial interest in rules that force everyone into monogamy—in such a world, the low-quality males do a lot better. similarly, some women are better off with enforced monogamy. this implies that—at least the possibility that—some modules are designed to try to impose certain sexual rules on other people. i think the way this works is through moral intuitions surrounding behavior like abortion, prostitution, and much else that might be associated with promiscuity or mating patterns. the key is that some people win and some people lose in the evolutionary sense under different regimes. i think this explains the large differences in views on sexual behavior. the issues surrounding sex and morality are, no doubt, going to turn out to be more complicated. My main purpose here has been to sketch what an argument might look like for explaining why people are inclined to constrain other people’s behavior. this type of explanation won’t be adequate for all moral intuitions, some of which don’t have a clear link to fitness interests. For example, moving from sex to drugs, people have a very strong intuition that many, indeed, most, recreational drugs should remain illegal. this intuition runs afoul of the principle of freedom that most people in liberal democracies endorse. to return to the example of banning sex, most people would agree that we ought not do that because people should be allowed to do what they want. Make no mistake, some people really, really want to do drugs, perhaps in a way that mirrors the way people really, really want to have sex. For whatever reason, we seem to have modules designed to work very hard to prevent people from doing the things they want to do. this is arguably one of the greatest inconsistencies of modern times, given that our press secretary modules, at least in the West, are always going on and on about our deep, fundamental abiding commitment to liberty, the point with which i close the book. But first, a moment to ensure i’ve explained to your satisfaction why everyone (else) is a hypocrite.