The Chronicle Review

Sex on the Mind

Keith Negley for The Chronicle Review

October 14, 2013

It is a truth universally acknowledged—at least by biologists—that every person owes his or her existence to parents who successfully reproduced, each of whom, in turn, had two parents who did the same ... and so on, going back hundreds of millions of years to the first ancestral blob (or two) of protoplasmic goo that trundled onto terra firma from the early earth's organic soup. From then on, no one's ancestors missed a beat.

As a strictly logical proposition, that observation is probably equivalent to the astounding fact that no matter how tall or short a person may be, her legs are always just long enough to reach the ground. Nonetheless, the universally shared, unbroken chain of successful breeding conveys a crucial biological truth: Reproduction matters.

Modern evolutionists, however, can be criticized for giving short shrift to the realities of reproduction. The most important conceptual advance in evolutionary science over the past few decades has been the recognition that natural selection acts at the level of genes rather than of species, groups, or even individuals. That perspective sees individual reproduction as only a special case of the fundamental evolutionary process, in which genes are favored insofar as they succeed in projecting copies of themselves into the future, housed in bodies that need not necessarily be their own offspring.

Hence the evolutionary bottom line—what is maximized by natural selection—is "inclusive fitness," which includes not only traditional Darwinian fitness (personal reproductive success) but also an indirect component of the enhanced reproductive success of relatives, with the importance of each devalued in proportion to the distance at which he or she is related.

Much of the intellectual excitement and empirical richness of evolutionary science in recent years have derived from studies revealing the power of that perspective. Nevertheless, there is still much to be said for plain old "direct fitness," bearing in mind that natural selection promotes personal reproduction because it is the most direct way by which genes project copies of themselves into future generations. Reproduction isn't opposed to inclusive fitness; it is simply the most straightforward technique to achieve it.

Yet evolutionary biologists have until recently given insufficient attention to straightforward breeding success—and failure. Moreover, even when it comes to looking at individual reproduction, the focus of behavioral ecologists has tended to be asymmetrical, examining particularly the actions of males­—even though the role of females in direct reproduction is nearly always more crucial. After all, in theory, at least, any male is capable of inseminating numerous females, whereas it is the success or failure of breeding females, based on their limited supply of eggs, that determines reproductive success. (That, incidentally, is why wildlife managers are typically inclined to institute a hunting season for bucks rather than does.)

Not to sound too stuffy, but the degree of breeding success (and failure) was good enough for Darwin and for the critters he studied, not to mention all the others. It is to be welcomed, therefore, that several books on evolutionary science this year are turning attention back to personal reproduction in Homo sapiens. That is, they're getting back to biological basics.

Grazyna Jasienska's The Fragile Wisdom, subtitled An Evolutionary View on Women's Biology and Health (Harvard University Press), may well be the best of the lot. Jansienska—a professor at the Institute of Public Health at Jagiellonian University Medical College, in Krakow, Poland—could be described as an evolutionary/obstetric/endocrinologic anthropologist, uniquely qualified to explore women's reproductive health from a perspective that is not only cross-cultural but also infused with evolutionary wisdom.

Her book is a revelation. Jansienska explains, for example (for the first time, in my reading experience), why it has been so difficult to prevent certain aspects of disease in women: because women are, unfortunately, victims of competing evolutionary pressures between their lifetime reproductive success—the focus of natural selection—and their lifelong health, which is of great concern to women and those who care about them, but not especially "privileged" by the evolutionary process.

In short, women's physiology has evolved to maximize their successful reproduction, not their health or happiness, and—especially once they are postreproductive—not their risk of disease and consequent suffering. A genetically facilitated tendency toward high levels of estrogen, for instance, has been selected for because it enhances fertility, despite the fact that such levels also increase the risk of developing breast cancer in later life. Consider, as well, that while many pregnant women in the West restrict calories and engage in vigorous exercise to promote their well-being, doing so also appears to trick their bodies into "thinking" that nutrients will be limited, which results in newborns with low birth weight. As Jansienska emphasizes persuasively, there are many such long-term trade-offs. Her book is intellectually invigorating—and simultaneously a bit dispiriting.

Although she stops short of being prescriptive, her work nonetheless points toward the prospect of practical interventions by the new field of evolutionary medicine, emphasizing "poor fits": between Stone Age physiology and modern lifestyles (notably with regard to exercise and dietary habits), between fetal and adult environments (what is good for the fetus isn't necessarily good for the mother, and vice versa), and between biology and culture (for example, we've evolved to cherish fats, sugars, and salt­—generally rare in our Pleistocene past, but artificially produced in dangerous abundance by today's technology).

In most disciplines, there are three kinds of books intended for the intelligent layperson. Some provide stimulation and insight even for specialists in the field; heading that list would be George C. Williams's Adaptation and Natural Selection (Princeton University Press, 1966) and Richard Dawkins's The Selfish Gene (Oxford University Press, 1976). The Fragile Wisdom belongs here.

Books in the second group are solid, occasionally prettified for the general reader but not offering much new for practicing scientists. Robert Martin's How We Do It: The Evolution and Future of Human Reproduction (Basic Books), although more serious than its title (which unfortunately sounds like a middle-school sex-ed book), fits into the second category. So do Evolution and Human Sexual Behavior, by Peter B. Gray and Justin Garcia (Harvard University Press), and Mating Intelligence Unleashed: The Role of the Mind in Sex, Dating, and Love, by Glenn Geher and Scott Barry Kaufman (Oxford University Press).

How We Do It is a sound but relatively pedestrian account of human reproduction with a comparative slant on our primate relatives, as might be expected from an expert on prosimians (tree shrews, lemurs, and so forth). Martin, curator of biological anthropology at the Field Museum in Chicago, asks what is natural when it comes to making and raising babies. (Breastfeeding, he says, probably evolved with an average age of 3 for weaning; babies may be ready for toilet training much earlier than we think.)

The book contains some delightful information. Did you know, for example, that in the 1760s, Lazzaro Spallanzani—who disproved the widely accepted doctrine of spontaneous generation—also outfitted male frogs with tight-fitting taffeta pants to demonstrate that amphibian eggs don't develop into embryos unless they are fertilized by sperm?

However, although Martin regularly brings his focus back to human beings, his analysis is sometimes imperfect. Thus, when discussing human polygyny (our "natural," biologically inclined mating system), he appropriately describes sexual dimorphism. The presence of males consistently larger than females correlates strongly with male-male competition, and so with harem-based breeding. But he would have made a stronger case had he mentioned two other key pieces of evidence for our polygamous nature: behavioral dimorphism (the tendency of human males, even juveniles, to be more aggressive than females) and the well-described asymmetry between men and women when it comes to preferring multiple sex partners.

Martin also fails to mention sexual bimaturism. One would logically expect that females would delay breeding until they are older, larger, and better able to undertake the demands of pregnancy and lactation, while males should begin when younger and smaller, since their only biologically mandated investment is a trivial squirt of semen. And yet it is a cross-cultural universal that girls become mature earlier than boys, a pattern found in all polygynous species. Why? Because the "harem-keeping" sex is forced to engage in strenuous social competition with other harem-master wannabes. Add the fact that more than 85 percent of human societies were preferentially polygynous before the cultural homogenization generated by Western missionaries, and humanity's "natural" harem-keeping proclivity is essentially proven.

Although the subtitle of How We Do It alludes to the future, the book gives scant attention to how we might actually "do it" in the years to come. It dutifully discusses birth control and assisted reproduction, both of which focus primarily on women, but neglects DNA testing, which promises to protect men from bogus claims of genetic fatherhood as well as hold them responsible for paternity.

Jansienska and Martin focus on reproduction by women, but Gray and Garcia look at sexual behavior as such, and at men no less than women—although the authors are more concerned with "how come?" than "how to?" Evolution and Human Sexual Behavior is sound, but unoriginal. Thus, it is a reviewer's worst nightmare: a very good book about which there is very little to write. Still, a strong case can be made that real sex education would go beyond Plumbing 101 and emulate this book—actually teaching about sexual behavior from an evolutionary perspective. With backgrounds in anthropology—Gray at the University of Nevada at Las Vegas and Garcia at the Kinsey Institute for Research in Sex, Gender, and Reproduction—the authors do an especially good job describing what William James might have called the varieties of sexual experience.

That is more unusual than one might think. Anthropologists have what might be labeled the Pago Pago problem: fear that when they identify a complex human behavior as a cross-cultural universal, someone in the audience will intone, "That's not the way they do things in Pago Pago." Hence it is especially refreshing to encounter members of the discipline who are comfortable with both biologically influenced behavior patterns and the remarkable range of human cultural diversity, and who have the wit and wisdom to combine the two—consistencies in pair-bonding and adolescent sexual development and variations in the desirability of mates worldwide—rather than argue vociferously that either precludes the other.

Still, Gray and Garcia fall flat when it comes to their discussion of female orgasm and menopause, embracing the ludicrous proposition that both are nonadaptive byproducts: the former a hitchhiker on male ejaculation and the latter a random consequence of recently extended human life spans. Suffice it to note that female orgasm, with all its Technicolor complexity, shows every sign of being a highly evolved and thus adaptive phenotype, while evidence is overwhelming that postmenopausal women contribute significantly to their genetic fitness via enhancing the survival and success of their grandchildren.

With a more how-to dimension, Geher and Kaufman's Mating Intelligence Unleashed offers a provocative concept, derived by applying evolutionary insights to mating, exploring such things as the role of personality in generating sexual attractiveness and whether nice guys do finish last. Geher, an evolutionary psychologist at the State University of New York at New Paltz, and Kaufman, a psychologist who teaches courses at New York University, show that the tendrils of evolution by natural selection extend far beyond the sex act, impacting a panoply of behaviors, including love.

Despite its retro comic-book cover, Mating Intelligence Unleashed unleashes some excellent science, buttressed by 35 pages of research references. Some readers will doubtless resent an evolutionary exegesis of their innermost traits and inclinations, especially when such insights threaten to unweave the rainbow of romance and love. But mating intelligence embraces an array of traits, including but not limited to humor, empathy, even artistic appreciation. It deserves recognition along with such other "intelligences" as verbal, numerical, structural, emotional, ethical, artistic, and so forth.

Each of these books offers genuine insights, or, at a minimum, factual accuracy. There is, regrettably, also a third component of this "pop science" triad: books that, to channel Dorothy Parker, should not be lightly tossed aside but instead "thrown away with great force." Notable in this category is Sex at Dawn: The Prehistoric Origins of Modern Sexuality (Harper, 2010), whose commercial success makes its egregious scientific blunders all the more galling. Christopher Ryan and Cacilda Jethá, a psychologist by training and a doctor, argue that human beings evolved in egalitarian groups that shared chores and sexual partners. Note: The "polyamory" the authors seek to promote is a far cry from polygyny, which is almost always associated with considerable mating competition. A pastiche of wishful thinking and grotesque and irresponsible misrepresentations of theory and data, the book might better be labeled Dreck at Dawn. It degrades the currency of those who struggle to honestly inform the reading public about important developments in science.

It is said that before one studies Zen Buddhism, mountains seem merely mountains, and rivers, rivers. Then, for those pursuing deeper understanding, everything is different ... until eventually, with enlightenment, the mountains are once again mountains and the rivers are rivers. The evolutionary study of reproduction is lot like that. Reproduction was initially seen as the evolutionary bottom line for all things, a straightforward Darwinian recognition—which changed when biologists comprehended the crucial primacy of gene-level selection. Of late, many evolutionary biologists have been returning to the straightforward mountains and rivers of regular old reproductive success. Whether this constitutes enlightenment or merely an overdue course correction remains to be seen, although, as with any good scientific pursuit, there are always more mountains to climb and rivers to navigate.

David P. Barash is an evolutionary biologist and professor of psychology at the University of Washington. His next book is Buddhist Biology: Ancient Eastern Wisdom Meets Modern Western Science (Oxford University Press, December).