True, new, and important: an introduction to the special issue.

In 1989, Leda Cosmides and John Tooby wrote the following in their contributed chapter to a book of "evolution-minded" research papers:

   Popular wisdom has it that arguments against new ideas in science
   typically pass through three characteristic stages, from

1. "It's not true," to

2. "Well, it may be true, but it's not important," to

3. "It's true and it's important, but it's not new--we knew it all along."

   If the papers in this volume are any indication, then the
   application of evolutionary biology to the understanding of human
   behavior has entered the "It's true but not important stage."
   (p. 277)

In the introduction to their chapter, Cosmides & Tooby were celebrating the growth of acceptance of evolutionary studies of human behavior from the stage of outfight hostility among many social scientists during the 1970s to the stage of grudging respect as the 1980s drew to a close. If the papers in this volume are any indication, however, we have finally entered the stage where numerous former critics are claiming that "it's true and it's important, but it's not new--we knew it all along." And it's about time!

In 1989, when Cosmides & Tooby wrote the chapter cited above, a special issue of The Journal of Sex Research devoted to evolutionary and neurohormonal perspectives would have been unthinkable. Evolutionary studies were viewed with profound distrust by many, and misunderstandings were even more widespread than they are currently, which is saying a lot. Although some continue to dispute various claims of scientists in fields of human evolutionary studies, relatively few would seriously argue that knowledge of the evolutionary history of our species is not relevant to an understanding of human psychology or sexuality. This is a major shift.

Nevertheless, the evolutionary perspective is not well represented in the field of sex research in general. This seems particularly odd, given that the theory of natural selection is, at its core, a theory of reproduction. While it may be easy to have sex without reproduction, it's not all that easy to have reproduction without sex, and many of the most important and influential theories and research projects to emerge from fields of evolutionary study of human behavior have been concerned with matters pertaining to courtship, mating, and sex or gender. The authors who have contributed to this special issue and I are therefore grateful to John DeLamater, Editor of JSR, for allowing us the opportunity to bring evolutionary perspectives to our readership, some of whom may not have been widely exposed to such perspectives.

This special issue of JSR is devoted not only to evolutionary perspectives, but also features neurohormonal research. Unlike evolutionary theory and research, sexual science has been widely informed by neurohormonal findings. However, from the evolutionary perspective, neural, hormonal, and biochemical substrates constitute proximate mechanisms by which ultimate mechanisms--evolutionary adaptations--are expressed and mediated. Detached from "evolution-mindedness," many sex researchers have used neurohormonal findings in an attempt to answer "why" questions, when, from the evolutionary perspective, such findings typically can only answer "how" questions.

Consider the question of the purported link between testosterone and aggression. If this link is genuine, and if it underlies the higher average levels of physical aggression found in boys and men relative to girls and women, knowledge of this link would still not answer the question of why boys and men are more physically aggressive than girls and women. "Why" questions demand ultimate answers, located in the adaptations (evolutionary history) of our species. "How" questions require proximate answers. Thus, testosterone may (or may not) turn out to be the "how" of greater average levels of male physical aggression, but it will never answer the question of "why" males are more aggressive (i.e., "why do men have more testosterone than women?").

Here is just one example of problems that may occur as a result of failure to incorporate both evolutionary and neurohormonal perspectives: Whereas the female reproductive cycle has long been understood by sex researchers in terms of neurohormonal events, the impact of the reproductive cycle on human female sexuality has, with few exceptions, been ignored. This is a result of the failure even of researchers who are not "biophobic" to incorporate evolutionary theory into their hypotheses. Consequently, virtually all of our knowledge of women's sexual psychology and behavior has been acquired through research that essentially averages data across the reproductive cycle. Researchers studying the sexuality of any other mammal would never even consider such a strategy.

An unknown number of erroneous conclusions about women's sexuality may have resulted from such practices. For example, Baumeister, Catanese, and Vohs (2001) put forth a strong empirical case to support their view that men have a more intense and constant "sex drive" than do women. They defined sex drive as intrinsic sexual motivation, "usually focused on craving for sexual activity and sexual pleasure" (p. 243). According to Baumeister et al., a person with a stronger sex drive has "more intense, and/or more frequent desires for sex" (p. 243), and these desires are for sex for its own sake, rather than in the service of other goals such as procreation, power, or stress relief. Moreover, these desires tend to override other, possibly conflicting desires. In contrast, a weaker sexual drive ought to "yield precedence" to other motivations and not produce behavior designed to promote or facilitate sexual experience (p. 244).

Baumester et al. (2001) reviewed abstracts for the entire publication history of The Journal of Sex Research and Archives of Sexual Behavior. They read all articles that measured sexual motivation in any form and also read all sources cited in these articles that referred to sexual motivation. They then conducted literature searches of PsycINFO and MEDLINE data bases, yielding a total of 5,400 articles on human and nonhuman animals. They excluded dissertations and research on nonhuman animals, and focused their attention on research with non-clinical samples.

They found substantial empirical support for their hypothesis: Men think about sex more than women, have more sexual fantasies and more spontaneous arousal, they masturbate more, they desire sex more frequently and with a greater number of partners, they are less willing to forgo sex, less likely to avoid sex, more likely to initiate sex, more likely to enjoy many types of sexual practices, more likely to sacrifice resources (e.g., money) to obtain sex, they have more favorable attitudes toward sexual behavior, they have less prevalence of hypoactive sexual desire disorder (HSDD), and they give higher self-report ratings for strength of sex drive.

This is powerful evidence indeed, and Baumeister et al. (2001) may well be correct in their assertion that the strength of men's sex drive is more constant and intense than that of women. They are certainly onto something, and there are solid theoretical grounds for anticipating such a sex difference. Because of the large disparity between men and women in the minimum possible parental investment necessary for reproduction, it would have benefited ancestral men to be interested in sexual behavior under a wide variety of circumstances. The contexts under which interest in sexual behavior would have benefited women reproductively were more limited (Symons, 1979).

However, virtually all of the data reviewed by Baumeister et al. were collected without controlling for women's reproductive cycle phase, and thus should be considered an average across the entire cycle. We really don't know if there is a true sex difference in the strength of sex drive, irrespective of reproductive cycle phase. Indeed, there are equally solid theoretical grounds for hypothesizing that the intensity of men's and women's sexual drive differs little or not at all--as long as the measurements are taken close to the women's mid-cycle (follicular phase; see Stanislaw & Rice, 1988; Wallen, 1995).

We are fortunate to have articles in this issue authored by a number of researchers--including Susan Bullivant and her colleagues, David Buss, Bettina Fischer, Karl Grammer, Martie Haselton, Martha McClintock, Elizabeth Pillsworth, LeeAnn Renninger, Kim Wallen, and Julia Zehr--who are concerned specifically with the importance of women's reproductive cycle to women's sexual psychology and behavior. Two of these articles, one authored by Bullivant et al. and the other by Pillsworth, Haselton, & Buss, are concerned with issues of measurement of women's reproductive cycle phase in the context of sex research. We hope these articles will stimulate more "cycle-consciousness" among sex researchers.

This special issue also includes an article on female intrasexual competition by Anne Campbell; a comprehensive evolutionary view of human mate choice by Dave Geary; a developmental view of the acquisition of templates for female attractiveness by Jennifer Connolly, Virginia Slaughter, and the late Linda Mealey, to whom this issue is dedicated; Catherine Salmon and Donald Symons' unique look at an unusual form of erotic media; an article by Dev Singh on the relationship between attractiveness and choice of mating strategy; and Melissa Hines, Charles Brook, and Gerard Conway's exploration of the role of androgens in the psychosexual development of men and women with congential adrenal hyperplasia (CAH). We are proud of the quality of scholarship and imagination represented in this issue.

Finally, I note that of the total of 29 contributors to this issue, 19 are women and 10 are men. If we remove from consideration the two articles strictly concerned with proximate neurohormonal variables and consider only the specifically "evolution-minded" articles, the tally is 11 female and 9 male authors. Thus, any way you slice it, women authors predominate. I draw attention to this for the following reason: Some commentators have asserted that evolutionary psychology, sociobiology, and similar fields are "male biased," promote "male perspectives," and have little to offer women scientists or women in general. Like so many other myths about evolutionary studies, this one is utterly unsupportable. If we have indeed moved into Cosmides & Tooby's third stage of argument against new scientific ideas, we are likely to hear fewer such assertions, and to benefit more and more from the incorporation of evolution-mindedness into all aspects of behavioral research. As Donald Symons, a founder of evolutionary studies of human sexuality, has noted, there is no such thing as "evolutionary psychology," because all scientific psychology must be evolutionary, by definition.

Many thanks to Martie Haselton for her comments on an earlier draft.

REFERENCES

Baumeister, R. F., Catanese, K. R., & Vohs, K. D. (2001). Is there a gender difference in strength of sex drive? Theoretical views, conceptual distinctions, and a review of relevant evidence. Personality & Social Psychology Review, 5, 242-273.

Cosmides, L., & Tooby, J. (1989). From evolution to behavior: Evolutionary psychology as the missing link. In J. Dupre (Ed.), The latest on the best: Essays on evolution and optimality (pp. 277-306). Cambridge, MA: MIT Press.

Stanislaw, H., & Rice, F. J. (1988). Correlation between sexual desire and menstrual cycle characteristics. Archives of Sexual Behavior, 20, 567577.

Symons, D. (1979). The evolution of human sexuality. New York: Oxford University Press.

Wallen, K. (1995). The evolution of female sexual desire. In P. R. Abramson & S. D. Pinkerton (Eds.), Sexual nature, sexual culture (pp. 57-79). Chicago: University of Chicago Press.

Address correspondence to Paul Okami, Ph.D., Department of Psychology, University of California, Los Angeles, 334 Kinsey, Box 951538, Los Angeles, CA 90095; e-mail: [e-mail]