It takes two: sexual strategies and game theory
Introduction
David Buss’s Sexual Strategies Theory (SST) is one of the major evolutionary psychological research programmes and has been very influential in the study of the human mind (see, for example, Buss, 1989, Buss, 1998, Buss, 2003, Buss, 2007b, Buss and Schmitt, 1993). This success, however, has not prevented it from also being very controversial: in particular, critics have questioned the interpretation and robustness of Buss’s empirical studies, and the theoretical and ideological presuppositions behind them (see, for example, Buller, 2005, Dupre, 2001; for some replies, see, for example, Buss and Haselton, 2005, Machery and Barrett, 2006, Delton et al., 2006, Carruthers, 2002).
Interestingly, though, there are two aspects of the theory that have received only very little attention to date, and that despite the fact that they relate to issues that, in their general form, have long been known about. These aspects are, firstly, the sex-specific methodology of the theory, and secondly, its conflation of the distinction between monomorphic and polymorphic evolutionarily stable states. However, as I seek to show in this paper, the lack of attention to these two issues is problematic, since there are good reasons for thinking that they make SST—at least as it is currently articulated—theoretically and empirically flawed.
More concretely, I argue that, firstly, without analysing mate choice as a game, no insights into what sexual strategies are likely to have evolved can be obtained. Only by taking the strategies of both sexes into account at the same time can evolutionary considerations be brought to bear on mate choice. While often acknowledged in passing, this point is still not sufficiently assimilated into the theory—and that despite the fact that a version of it had already been articulated by Dawkins (1976). Secondly, I try to show that, even if Buss did provide the relevant game theoretic analysis, SST would not yet be shown to have explained the origins of our sexual strategies. The reason for this is that the data Buss presents and analyses fail to clearly distinguish between evolutionarily stable states involving a monomorphism of complex strategies and those involving a polymorphism—a distinction that, as has been made clear by Orzack and Sober, 1994, Thomas, 1984, and Bergstrom and Godfrey-Smith (1998), needs to be respected for a trait to be corroborated as an adaptation.
Before laying out this criticism in more detail, though, it is useful to be more explicit about what, exactly, its scope is. As it turns out, this scope is at the same time quite restricted and quite wide-ranging. It is restricted, in that the focus of the criticism presented here is strictly on Buss’s version of SST. This is important, as his is not the only evolutionary approach to the study of how we make mating decisions (for alternatives, see, for example, Gangstead and Simpson, 2000, Li and Kendrick, 2006). Since these other theories are quite different in structure from that of Buss, one must not assume that the worries raised here automatically affect them also. On the other hand, the scope of the present discussion is also quite wide-ranging, in that the issues raised here apply, at least in principle, to any evolutionary psychological theory that is concerned with matters of social interaction. This is important, as it may entail that other parts of evolutionary psychology, too, would profit from closer attention to their game theoretic presuppositions. While spelling this out in more detail calls for a paper of its own, it is enough for present purposes to note that the discussion here has at least great potential relevance for many other parts of evolutionary psychology as well.
This paper is structured as follows. In Section 2, I set out the key aspects of Buss’s theory. In Section 3, I show why introducing game theory explicitly into the framework of the theory is necessary to make it theoretically compelling. In Section 4, I show why a closer attention to the monomorphism/polymorphism distinction is necessary to make it empirically compelling. I summarise the argument in Section 5.
Section snippets
Sexual Strategies Theory
Mate choice is a hugely important event for all sexually reproducing organisms: as one of the key factors determining their reproductive success, it contributes directly to their biological fitness (see, for example, Sober, 1993). According to evolutionary psychologists, events of this kind—that is, types of behaviours having a major adaptive importance—tend to lead to the evolution of psychological mechanisms that help the organism to shape them to its advantage (see also Cosmides & Tooby, 1992
Game theory and Sexual Strategies Theory
When Buss’s theory is discussed (both by defenders and detractors of it), it is frequently remarked that deriving sex-specific sexual strategies from claims about minimal parental investment alone is overly hasty. Since mating is a cooperative venture, both sexes need to be taken into account simultaneously when reasoning about the evolution of their sexual strategies (see, for example, Buss and Schmitt, 1993, Buss, 1992, Fernald, 1992, Buller, 2005). In fact, a version of this point had
States, strategies, and sexual strategies
In order for SST to be a convincing and interesting contribution to psychology, it needs to be empirically substantiated. To be clearer about what exactly this requires, it is useful to begin by noting that, at bottom, SST has two major aims: firstly, it seeks to provide an account of which sexual strategies we pursue, and secondly, it seeks to provide an account of why we pursue these strategies. Therefore, for SST to be empirically corroborated, Buss must show, on the one hand, that we in fact
Conclusion
I have tried to argue that Buss’s theory rests on weak theoretical and empirical foundations, unless it takes into account the fact that the two sexes were engaged in a strategic interaction. This need not mean that its conclusions are wrong, but it does point to the fact that, as it stands, it is intellectually unconvincing. Firstly, this is because the selection of cooperative strategies cannot plausibly be analysed without taking into account both partners of the exchange—only by doing that
Acknowledgements
I would like to thank Elliott Sober, Dan Hausman, Lawrence Shapiro, and an anonymous referee of this journal for useful comments on previous versions of this paper.
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