Evolutionary Psychology

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Robert Kurzban

The Evolutionary Psychology Blog

By Robert Kurzban

Robert Kurzban is an Associate Professor at the University of Pennsylvania and author of Why Everyone (Else) Is A Hypocrite. Follow him on Twitter: @rkurzban

What the Decision Letter Should Have Said

Published 16 March, 2011

Dear Dr. Conley,

Thank you for submitting your manuscript, “Perceived Proposer Personality Characteristics and Gender Differences in Acceptance of Casual Sex Offers” to the Personality Processes and Individual Differences section of the Journal of Personality and Social Psychology.

I have now received three reviews, and as you will see, the referees have suggested publication of your manuscript. In retrospect, I should have sent the paper to one or more reviewers with training in evolutionary psychology, because I have decided to override their recommendation due to some serious issues the reviewers did not address. I hope the comments below will be of use as you revise the manuscript.

The issue you address is a potentially interesting one, possible alternative explanations for the results of the classic study by Clarke and Hatfield in which confederates approach members of the opposite sex approach people on a college campus and ask one of three questions: “would you go out tonight?”, “will you come over to my apartment” and “would you go to bed with me?” As you report, in the last of these three treatments, no women but three quarters of men said “yes.”

The usual explanation one finds is based in Sexual strategies Theory (Buss & Schmitt, 1993). This theory suggests that men and women have different adaptations designed around the different adaptive problems faced by males and females, built on Parental Investment Theory (Trivers, 1972). Because of much greater female parental investment, female humans – as in other species – have adaptations designed to make them choosy, as each copulation is a potentially large fitness cost.

Here is where one difficulty lies. While you also allude to this issue of investment, you suggest that “From a sexual strategies perspective, women need to be “choosy” in terms of sexual encounters because they have very few ova…” The number of ova is not relevant; even if there were many more, the issue of investment would still give rise to adaptations to be choosy. You make this mistake again when you write, “Based on SST, the women in the Clark and Hatfield (1989) study were being selective in their choice of sexual partners, because their ova are a precious commodity.”

Further, you write that the theory says that “women are motivated to find the sexual partner most likely to support them and their children, as this provides the greatest hope of ensuring the survival of their genetic material over time.” This isn’t quite right, as it suggests a direct link between the adaptive problem and the motivation. Please have a careful look at Symons (1992), which will be useful to help you work through this issue.

You similarly write, that SST suggests that “Men’s desire for women stems from men’s desire (a) to spread their sperm indiscriminately and (b) to spread their sperm to women who are likely to bear children.” This is another instance of the same error. The claim from SST is not that men have these desires. The claim is that men’s preferences and strategies can be explained by the adaptive problems they faced. It is a crucial distinction you blur here and elsewhere.

Considerably more importantly, your exposition of the theory has some difficulties. You suggested “Pleasure Theory” as an alternative account:

The central thesis of pleasure theory is that the pursuit of pleasure is the central force that motivates sexual behavior (Abramson & Pinkerton, 2002). According to this theory, sexual reproduction is a by-product of sexual pleasure, rather than the reverse. Pleasure theory asserts that pleasure itself is evolutionarily favored; if humans are having pleasurable encounters, enough instances of vaginal intercourse will occur to ensure the survival of the species.

Taking the last part first, “survival of the species” confuses the level at which selection operates. Please have a careful look at Dawkins (2006) for an introduction to these ideas, which I strongly suggest you engage if you are going to continue to do work that touches on evolutionary ideas.

Next, your claim that the theory says that “sexual reproduction is a by-product of sexual pleasure, rather than the reverse” is a very odd claim. The “reverse” of this would seem to be that sexual pleasure is a byproduct of sexual reproduction. As far as I know, no one has ever made that claim, in part because it is – and I hope you will forgive some strong criticism here, which I make only improve the paper – essentially incoherent.

A byproduct is, as you probably know, an aspect of the phenotype that does not itself contribute to reproductive success, but is a side-effect of a trait that does;a belly button, for instance, itself has no function, but is a result of umbilical cords, which do, and leave the belly button as a side effect. So, one might say something like: “belly buttons are a side effect of umbilical cords, but do not themselves contribute to reproductive success.” All byproduct claims have this sort of structure. A [trait] is a by-product of [adaptation], but does not itself contribute to reproductive success. So it makes no sense to say: “Sexual reproduction is a byproduct of sexual pleasure, but does not itself contribute to reproductive success.”

I think the argument that you want to engage is the one that evolutionary psychologists typically make about sexual pleasure, which is that it is an adaptation, not a byproduct, and in particular that it is the motivational system that causes people to seek sexual encounters. An excellent source here is Jared Diamond’s book, Why is Sex Fun. (Please see p. 5 of the book you cite, With Pleasure, which portrays this argument reasonably well.)

More generally, I found it difficult to understand what you mean, then, when you say: “Pleasure theory asserts that pleasure itself is evolutionarily favored.” There is a sense in which this just is the standard view, but it’s difficult to know what you mean by this claim.

This isn’t to deny, of course, that people seek sex because they enjoy it. But of course this is a proximate, rather than ultimate explanation. Sexual Strategies Theory, against which you set Pleasure Theory, is at the ultimate rather than proximate level. Please see Scott-Phillips et al. (2011) for a recent discussion of this distinction. Some explanation for why people have the pleasure systems that they do is required. Simply assuming the pleasure systems are as they are and that people seek pleasurable experiences is not a theory or explanation as these terms are usually used. (You allude to being aware of this issue when you write, “I am not entirely convinced by the argument that sexual pleasure is a different level of analysis. That is, the implications of SST are clearly that women would forgo sexual pleasure to have sex with a high-status man who would support them and their potential children. Thus, for women, at least, pleasure is intentionally discounted within SST.” I was unable to understand the second two sentences, so I cannot respond to your being convinced by the ultimate/proximate distinction, but I do encourage you to engage witht this idea.)

I am afraid that these theoretical difficulties are sufficient to preclude publication in JPSP. Of course, you report a number of results from pen-and-paper versions of the Clarke and Hatfield work, and it could be that suitably framed, they would make a nice contribution.

Having said that, I would urge some care in how you present the results. In your discussion, you write:

if men’s central goal, as suggested by SST, is to transfer their genetic material to future generations, men should have a greater base rate likelihood of accepting a sexual offer from any woman than women have of accepting a sexual offer from any man, regardless of the proposer’s attractiveness (i.e., women should be choosier than men). SST does not predict that women would be equally likely to accept offers as men when (a) the proposers are very attractive, (b) the proposers are very unattractive, (c) the proposers are familiar people, and (d) the proposer and the individual are of the same sex.

I think it is quite incorrect to say that SST makes these predictions. For instance, you find that men report a certain disinclination to have sex with Rosanne Barr, and you find that there is no sex difference between men’s inclination to have sex with Angelina Jolie and women’s inclination to have sex with Johnny Depp. While I think there is some reason to worry about why it is that (some) men (say they would) turn down sex with relatively unattractive women, I think that a careful reading of SST suggests that the theory does in fact predict that woman might be interested in having sex with very attractive men, even if it is in the context of a short term encounter. (You might want to have a look at Meston & Buss, 2009). In short, your portrayal of SST is somewhat less complex and nuanced than most readings of the theory take it to be.

Broadly, your manuscript in its present form contains serious errors that must be corrected before publication could be considered. I hope these remarks are useful to you.


The Editor

ps (Back in Rob persona now): I actually have no idea who edited this manuscript or reviewed it.


Abramson, P. R., & Pinkerton, S. D. (2002). With pleasure: Thoughts on the nature of human sexuality. New York, NY: Oxford University Press.

Clark, R. D., & Hatfield, E. (1989). Gender differences in receptivity to sexual offers. Journal of Psychology and Human Sexuality, 2, 39–55.

Dawkins, R. (2006). The Selfish Gene: 30th Anniversary Edition. Oxford: Oxford University Press.

Meston, C., & Buss, D.M. (2009). Why women have sex. New York: Holt.

Scott-Phillips, T.C., Dickins, T.E. & West, S.A. (2011) Evolutionary theory and the ultimate/proximate distinction in the human behavioural sciences. Perspectives on Psychological Science.

Symons, D. (1992) “On the use and misuse of Darwinism in the study of human behavior” in Barkow, J., Cosmides, L. & Tooby, J. (eds) (1992) The Adapted Mind: Evolutionary psychology and the generation of culture (New York: Oxford University Press)

Trivers, R.L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.), Sexual selection and the descent of man, 1871-1971 (pp. 136–179). Chicago, IL: Aldine

Copyright 2011 Robert Kurzban, all rights reserved.

Opinions expressed in this blog do not reflect the opinions of the editorial staff of the journal.