Why Evolutionary Psychology Is Not Mere Speculation or "Just So" Stories: With Examples from Human Sexuality and from Narratives

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Contrary to what some of its opponents claim, evolutionary psychology is not mere speculation, or "just so" stories which are incapable of being tested. Many believe these critiques. In fact, a former colleague of mine, now a journal editor, recently stated them to me in an e-mail. He mentioned Stephen Jay Gould, who has made such criticisms (Gould, 1997). Influential people like Gould have advanced these critiques, and they were once somewhat true, when evolutionary psychology was called sociobiology. In the early days of sociobiology, there was much speculation with little empirical or quantitative assessment. In fact, I was initially turned off by that reality. But, this is no longer true. Sociobiology, with its emphasis on biological explanations of apparent social realities (E. Wilson, 1975) has evolved into evolutionary psychology, with its emphasis on how the brain evolved over time, and how our desire to survive and to spread our genes into future generations determines much of what we do (Barkow, Cosmides, & Toby, 1992; Buss, 1999; Dawkins, 1989). Sociobiology or evolutionary psychology both now use empirical methods of observation, and subject data to statistical analysis. Of course, any science uses speculation, theory, etc. But, these are used in the service of a scientific approach, and the old criticisms are now mostly inaccurate. The concept of evolution is the unifying concept in biology. Bringing this concept into psychology has provided many new insights. Evolutionary psychology is one of the most important new theories of our time, applying Darwin's insights about evolution and natural selection (Darwin, 1859, 1868, 1871, 1872) to human psychology.

There has been, in my opinion, a paradigm shift in psychology, such that many things explained in terms of social causation--or not explainable well at all--are now explained in evolutionary psychology terms. Thus, evolutionary, biological explanations have become more frequent in psychology, while explanations in terms of social psychology, learning or culture have become seen as less useful. Nature and nurture work together, so these other areas are not rejected, they just are not used as much anymore as the primary explanation of things. I shall provide examples of how the new evolutionary psychology explanations provide important insights, not previously available.

Human Sexuality

Evolutionary psychology has been especially helpful in the area of human sexuality, where our understanding lags behind the importance of an area that affects us all. Not only would the human race not survive but for heterosexual attraction and heterosexual intercourse. But also, there are many important aspects of human sexuality, including both biology and male-female relationships, that are poorly understood. There are four areas in which evolutionary psychology provides extremely important insights, and in which other fields seem unable to explain well what is occurring. Other fields have some insights, but nothing like that provided by evolutionary psychology. The four areas that seem especially important to me and in which evolutionary psychology provides excellent insights are the preference of both males and females for sexual intercourse over masturbation; the preference for males, as they age, for younger female partners; female sexual desire during ovulation; and, differences in male vs. female jealousy. I have discussed these briefly before (Eisenman, 2001a) but will discuss them here in greater detail, and add some new studies.

Sexual Intercourse vs. Masturbation

At first glace, it might seem obvious that people prefer sexual intercourse to masturbation. For one thing, our culture often puts down masturbation, and makes it seem like some undesirable thing only engaged in by people who are disturbed, or who are deficient because they cannot obtain a partner. However, the reality is much more complex. Famous sex researchers Masters and Johnson (1966) found that masturbation provides more physiological intensity (presumably enjoyable intensity) for both males and females than does sexual intercourse. …