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Natural Selection of Culture?

Culture and the Evolutionary Process

by Robert Boyd, by Peter J. Richerson
University of Chicago Press, 331 pp., $29.95

The formal similarities between biological evolution and human history have repeatedly tempted students of one topic to borrow ideas from the other. The most famous and fruitful example of borrowing by biologists of an idea from the human sciences was the use made, by both Darwin and Wallace, of Malthus’s picture of human competition for resources as a foundation for their own theory of evolution by natural selection. At a less exalted level, I have myself spent much of the last fifteen years applying the mathematical theory of games, first developed for use in economics, to solve problems in evolution. Indeed, I am by no means the only recent biologist to exploit mathematical economics as a source of ideas.

Biologists have, by and large, been eager to borrow ideas from the human sciences. Borrowing in the other direction is less well regarded. The reason for this ill repute is not far to seek: biological ideas have too often been used, not as potentially valuable research tools, but as a moral justification of policies that might otherwise seem dubious. The Social Darwinists, at the end of the last century, used Darwin’s ideas to justify laissez-faire capitalism and to oppose economic measures aimed at helping the underprivileged. More recently, the Nazis used biological terminology—they can hardly be said to have used biological ideas—to justify genocide. It would, however, be a great pity if this improper transfer of ideas from biology to the human sciences were to blind us to the possibilities of a fruitful transfer. Boyd and Richerson’s book, which offers a Darwinian theory of the evolution of culture—“the transmission from one generation to the next, via teaching and imitation, of knowledge, values, and other factors that influence behavior”—is the outcome of much hard and careful thinking. I approached it with a good deal of distrust and trepidation, but am persuaded that they have something of real value to offer.

It may be as well to start by explaining what they do not say. They are not offering a genetical interpretation of society. There are, in fact, two very different kinds of genetical interpretation possible. The first, and less plausible, is the view that the differences between societies are caused by genetic differences between the members of those societies. The most consistent proponent of that view, the late C.D. Darlington, went so far as to argue that language differences are in part caused by genetically determined differences in the vocal tract, and that what is wrong with British agriculture is that the farmers are too inbred.

Boyd and Richerson have little sympathy with this view, even in its less extreme forms. They think that the evidence tends to show that the genetic causes of cognitive and temperamental differences between races are of trivial importance. There is, however, a very different, but still genetical, view. This is that there are universal features of human nature that determine the nature of human societies. There is a sense in which this is obviously true. The reason why human societies are different from the societies of chimpanzees or hunting dogs is that human beings are genetically different. However, Boyd and Richerson argue that the nature of specific human societies cannot be explained merely by the interaction between a universal human nature and the nature of the environment—of soil, climate, and so on. This is so because the behavior of human beings is determined, not only by their immediate environment, and by the information coded in their genes, but by information that is culturally transmitted. It is the nature and effect of this cultural transmission that they discuss in this book.

They define culture as “information capable of affecting individuals’ phenotypes which they acquire from other conspecifics [i.e., members of the same species] by teaching or imitation.” The critical word here is “information.” They picture a person’s behavior as being determined by his or her immediate environment, and by two kinds of information, transmitted along two channels, one cultural and one genetic: hence they write of a “dual inheritance system.” There is nothing about this picture that one could easily object to, and nothing about it that is particularly novel either. What is novel is the way in which they analyze the behavior of such a system by borrowing concepts, and a style of thought, from evolutionary biology.

Their method is to construct simple mathematical models, aimed at studying the effects of different assumptions that can be made about the way an inheritance system works. Why do they concentrate on simple models? Any simple model of culture will leave out of account many important factors. Should we not, therefore, put into the model everything that we think might be important, even if the price is to end up with a very complex model? The experience of biologists has been that the construction of such complex models is a waste of time, essentially because, as Boyd and Richerson rightly say, “To substitute an ill-understood model of the world for the ill-understood world is not progress.” It has also been our experience that very simple models can be helpful in answering important questions. To give examples, the questions I have myself tried to answer using simple models include: “Why are the two sexes different?” “Why are some species composed of males and females, and others of hermaphrodites?” and “Why are some hermaphrodites capable of self-fertilization, and others not?”

There are two reasons why simple mathematical models are helpful in answering such questions. First, in constructing such a model, you are forced to make your assumptions explicit—or, at the very least, it is possible for others to discover what you assumed, even if you were not aware of it. Second, you can find out what is the simplest set of assumptions that will give rise to the phenomenon that you are trying to explain. For these reasons it is increasingly the case, both in ecology and evolution theory, that anyone who claims that he has an explanation of some phenomenon is expected to back up his claim by presenting a formal model. This style Boyd and Richerson adopt in their book. Some readers may find the method discouraging. However, they can follow the main theme of the book while skipping the mathematical bits; the advantage of including the mathematical demonstrations is that, when in doubt, you can find out what they are really saying, and can confirm that their conclusions really do follow from their assumptions.

Their book is not the first attempt to develop formal models of cultural inheritance. Two previous attempts were made by L.L. Cavalli-Sforza and M.W. Feldman, and by C. Lumsden and E. O. Wilson. The second of these is deeply unsatisfactory, for reasons I have discussed elsewhere.* Cavalli-Sforza and Feldman, in contrast, did an excellent and scholarly job in a book published in 1981, and their work has been built on by Boyd and Richerson. However, I did find the present book more rewarding, for a number of reasons. Their review of empirical data from the social sciences, both in support of some of the assumptions of their models, and to illustrate the phenomena that their models might help to explain, is much richer than in the earlier book. They analyze a wider range of models, and so reach more conclusions, and in particular more unexpected and unobvious conclusions. They make a greater effort to place their own work in the context of what others have done. Finally, they tackle a problem that is of particular interest to me as an evolutionist: How can we explain the genetic evolution of those human characteristics that are needed if extensive cultural inheritance is to be possible?

In addition to borrowing a style of analysis from biology, they have also borrowed the central concept of natural selection. As was clear to Darwin, selective survival and reproduction will cause change, but only if the traits that influence survival are inherited. If cultural traits are inherited, by teaching and imitation, and if different traits have different likelihoods of being transmitted, then the Darwinian model of evolution by natural selection applies, even though the inheritance is not mediated by DNA.

To see what this view implies in more detail, and, incidentally, to see what Boyd and Richerson have in mind when they speak of simple models, consider the two following possibilities. First, suppose that a child acquires some particular cultural trait from one or other of its parents, with equal likelihood, such as a tendency to be altruistic. Suppose further that some variant of the trait causes its possessors to have, on average, more children than they would have if they had not acquired the trait. Then that variant will become more common, by a process exactly analogous to the spread of a genetically determined trait by natural selection.

Now consider an alternative model, in which differences in biological fecundity play no role. Suppose that individuals acquire some trait by imitating, not their parents, but some other member of their social group. They tend to imitate those members who are “successful” according to some criterion: For example, to offer an implausible fantasy, they imitate those professors who attract more students to their lectures. Then, if some cultural variant leads to success (i.e., to attracting large audiences), that variant will tend to become common in the population.

I have deliberately chosen two of the simplest possible models of the natural selection of cultural traits, so as to bring out the gist of the author’s argument. When they speak of the natural selection of cultural traits, they think that such selection brings about evolutionary change because those traits are culturally inherited through imitation and teaching: No genetic change need occur. They recognize, however, that there are two important ways in which the analogy between cultural and biological evolution breaks down. In biology, mutations are nonadaptive—i.e., they do not, in most cases, increase the fitness of the organism—and acquired characters are not inherited: In cultural inheritance, the analogous statements may not be true. Boyd and Richerson seem to give little importance to the faculty of reason. They do accept that a person is more likely to acquire a new habit if he thinks it will pay him to do so, although they argue that the connections between human actions and their consequences are often so hard to calculate that we tend to rely on custom rather than reason. All the same, the existence of human reason does mean that cultural innovation, unlike mutation, can be adaptive. The need to allow for the inheritance of acquired characters is even more obvious: If I learn something I can tell my children and have some hopes they too will learn it.

My own suspicion is that these structural differences between culture and genetics will inevitably limit the usefulness of the kind of theory presented in this book. The explanatory power of evolutionary theory rests largely on three assumptions: that mutation is non-adaptive, that acquired characters are not inherited, and that inheritance is Mendelian—that is, it is atomic, and we inherit the atoms, or genes, equally from our two parents, and from no one else. In the cultural analogy, none of these things is true. This must severely limit the ability of a theory of cultural inheritance to say what can happen and, more importantly, what cannot happen.

I conclude this review by considering one particular model in some detail. In a chapter which opens with an account of the Japanese kamikaze pilots in the last world war, the authors develop a theory to account for the tendency of human beings to behave altruistically toward the groups to which they belong by making sacrifices for the common good. In their view, the beliefs that led the kamikaze pilots to die for their country are an extreme example of such tendencies. Biologists have spent much time on the analogous phenomenon in animals: We have explanations—such as the fact that the altruist may share genes with the recipient of its altruism, and it is genes, not individuals, that matter in evolution—but they are ones that work only for altruistic behavior among the members of small groups. Boyd and Richerson start by analyzing a model in which individuals acquire cultural traits by copying those that are most common in the population. Of course, if I copy the first person I meet, then I am more likely to acquire a common than a rare trait, but Boyd and Richerson are here assuming a more extreme form of imitation in which I adopt whichever trait I observe to be most common, after observing many people. They show that such a “conformist” habit of acquiring culture can be an advantage to the individual in a variable environment, in which different traits are favored in different places. This, they suggest, has led to a tendency to adopt, when in doubt, whatever are the common beliefs and customs in the society to which one belongs. I am not clear whether they think that this conformist tendency is genetically programmed, or itself something that evolves culturally.

So far, there is nothing in the argument to imply that these customs should be self-sacrificing. At this point, therefore, they introduce the concept of “cultural group selection.” Given conformist individuals, they show that cultural differences between groups will be exaggerated. If the cultural practices of different groups differ in their effectiveness in ensuring the long-term success of the group, then group selection can lead to the evolution of cooperative and self-sacrificing practices. For example, note that the argument is that cultural, not genetic, evolution will occur. All that is perhaps genetic is the conformist habit in acquiring culture.

The argument is ingenious, and I think it is logically sound, but I am not convinced that it is either necessary or sufficient for explaining the evolution of cultural traits. First, is it necessary? Boyd and Richerson argue that it is hard to account for altruistic behavior in large groups if behavior is rational, even if everyone would benefit if everyone else was altruistic. Essentially their reason is that it is hard to explain, on purely rational grounds, why individuals in a cooperative society do not take the benefits of cooperation without paying the full costs. I do not see their difficulty. In the society I inhabit, public goods like roads, services, and even a health service are paid for by taxes. If I do not pay my taxes, I am punished, so it is rational to pay taxes. If I am asked, as I am every five years or so, whether I prefer that everyone should pay taxes and should have access to public goods, or that taxes should be reduced and the public goods disappear, it is rational for me to vote for the former. Of course, looking at the world as it is, no one could suppose that reason always leads to beneficial cooperation. The breakdown of rational cooperation arises, I think, because of the existence within society of different groups with different interests.

The difficulty for any account of society that assumes that individuals behave rationally is partly that experimental psychologists find little support for such an optimistic view. For example, people form conclusions on the basis of insufficient data, and are then reluctant to change their minds when confronted by disconfirming evidence. It is also partly that the world is full of groups whose behavior benefits neither the group as a whole nor the individuals that compose it. The activities of most terrorists are unlikely to benefit either the individual terrorist, or the group to which he belongs, or the cause for which that group claims to be fighting. Such groups are often motivated by fanatical beliefs which, to outsiders, seem irrational and self-destructive. The argument developed by Boyd and Richerson perhaps does something to explain such fanaticism, but I wonder whether it is sufficient to explain it. I do not have anything better to offer. The capacity of our species, for good or ill, to be swayed by myths I find a continuing and as yet unanswered puzzle.

I found this book much more fun to read than I had expected. It can be read without following all the mathematics in it, but as I have noted it is important to have the mathematics there, so that one can on occasion find out exactly what Boyd and Richerson mean, and can satisfy oneself that their assumptions really do lead to their conclusions. They have made a brave attempt to integrate their abstract models with data from psychology and anthropology. They have helped to distinguish between and to evaluate different theories of sociobiology and of culture. They have proposed a number of ingenious models to account for the behavior of the oddest species that has yet evolved.

  1. *

    J. Maynard Smith and N. Warren, “Models of Cultural and Genetic Change,” Evolution, Vol. 36 (1982), pp. 620–627.

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