American Scientist

Ever Since Adam and Eve: The Evolution of Human Sexuality. Malcolm Potts, Roger Short. 365 pp. Cambridge University Press. $29.95 (paper).

Sex sells, and that might be reason enough for this handsome new book to be successful. But Darwinism is also a sexy topic these days. The recent paroxysm of books announcing the death, once more, of Darwinism seems to be subsiding. In its place is a steadily growing number of books promoting the insights that the Darwinian theory of natural selection can bring to medicine, psychology, economics, political science, computing, cognitive science or industrial design. Its appeal lies in bringing intellectual clarity to most complex of problems.

Darwinian reasoning is the knife to cut through the knots of complicated systems, with their imposing multitude of individuated actors and their many-layered networks of multiple causation. Scientists confronting complex systems, having rejected earlier simplistic reductionism, still seek the simplifying model. They aim not to reduce the complexity but to acknowledge it and yet gain a sense of explaining the system as a whole. For this, Darwin's great insight still is productive: The dynamic interactions of competing entities do resolve naturally into ordered systems, with adaptive solutions to problems in context. Viewing structure as adaptive leads one, before the detailed tracing of the paths of causation, to a set of expectations and possible constraints. It makes sense of the situation. In the best hands, such reasoning should tell us why particular agents and contexts led to the distinctive organization of the world that we see, explaining anything from the form of the keyboard used in writing this sentence to why we get sick. That is the kind of making sense that Malcolm Potts and Roger Short have attempted for human sexuality.

Their wit is revealed from the opening moments, with a title that is a play on both creationism and Stephen Jay Gould's Ever Since Darwin (1977), that remarkable set of essays that opened with a paean to Darwin's brilliant insight (natural selection) and closed with a balanced critique of the new field of sociobiology. Potts and Short surely hope to attain a similarly wide audience, and they have provided an engaging popularization of the evolutionary treatment of sex. No doubt they also wish to show us just how useful sociobiological reasoning has turned out to be after 20 years of criticism and development. Indeed, the subtitle is something of a misnomer, for it is not the "evolution" of sexuality, step by step, that fills these pages so much as a Darwinist foundation for understanding its peculiar logic. They might have called it "the adaptive foundation of human sexual behavior." Nonetheless, they do wield the tools of evolutionary analysis with skill, bringing to bear comparisons with animal relatives near and far, close looks at the great apes, and cross-cultural human universals and distinctions. There is also much of the here and now, explaining the empirical details of hormones, development and organ systems that one might expect from two distinguished reproductive biologists.

The central model is standard sociobiology, analyzing asymmetrical investments of energy and time by females and males in reproduction. Specialists will not find much new argumentation, although there occasionally are handy details from a broadly read empirical literature. What makes this book distinctive is its smooth blending of the mechanics of molecules and organs, the genetic logic of evolutionary strategies and the context of particular sexual behaviors. That Potts and Short do this more often with anthropological comparisons and an awareness of human cultural diversity than with naive talk of a "gene for x" makes it all the more refreshing. There are also occasional nifty twists in the models. Early on, they push the new emphasis in sexual-selection models of female choice, which makes for some subtle shifts of language. A "harem" situation, such as with red deer, is no longer a single male dominating a set of females but many females sharing one male for his single function, providing gametes of acceptable quality to them.

Nonetheless, the standard model is imbued with distinct differences between the sexes, in everything from muscle mass and hormonal effects to brain structures and linguistic tendencies. The central problem is to explain a human sexual dimorphism that is somewhat in the middle of the range for the primates. The social fact of importance is the propensity for male polygamy and female monogamy, expected theoretically from asymmetrical investment and from the physical differences between the sexes. The authors do not shy away from strong claims on such differences but derive little morality or politics from them.

They also indulge in few of the simplistic leaps that characterize much human-sociobiology popularization and even some of the serious literature, where the low cost of sperm production is held to explain directly why your 47-year-old male colleague is suddenly driving a red sports car with his trophy wife beside him. This is far more subtle, at least partly because they take seriously the profuse diversity of human cultures. It is also an acknowledgment that, historically, in a world "complicated by economics, politics, religion and the law, which have become predominantly male preserves, the innate reproductive agenda of the female has often become subordinate to that of men." Potts and Short seem uninterested in simply writing the experience of Western white men into biological law. Ethnographic comparison becomes neither facile universalizing nor an impediment to shared causes but part of the wonderful complexity that a Darwinian approach can dissect. They hope, as they repeatedly offer, that understanding a full model of investments and benefits, for both sexes, will open our eyes to our behavior and allow reasonable choices about sexual lives.

Nonetheless, there are gaffes. Their explanation, for instance, of the female's strategy in cuckoldry falls into a trap of their own model. Potts and Short present it as the female surreptitiously attempting to conceive and have her resource-providing partner raise unrelated offspring. Why she should, genetically, wish to do so is not addressed. In treating the different strategies of men and women in reproductive partnership, moreover, they develop a strong model of differential drives. Males end up more interested in sex and resource competition, females in emotions and resource insurance. Sex and emotion are the bonding cement of sociality, deeply embedded as biological desires. So, then, why couldn't the female cuckold be seeking emotional satisfaction denied by a resource-providing mate, rather than a simple genetic benefit? One might wish for an empirical constraint, such as cross-cultural studies of whether unfaithful wives are seeking pregnancy or not.

Where the logic jars, it is usually a matter of mixing levels of cause and effect too easily or leaping too quickly to an apparently obvious genetic story. What is notable, however, is how seriously the authors take the consideration of two agendas in a sexually dimorphic species. A theme throughout is that human life is characterized by compromise and richly diverse flexibility, deeply affected by cultural norms and traditions.

Refreshing is also the word for their style, breezy yet serious, filled with small details that often simply delight. It is a beautifully produced book, on heavy, slick stock that holds the image crisply and richly, and the classical paintings and dramatic photographs that dot the book glow on the page. It's frequently clever, such as the page with a photograph of pygmy chimpanzees, copulating for social reassurance, facing a shot of Ronald Reagan and Margaret Thatcher smiling together, as "sociable or submissive" primate behavior. They do not shy from the sexy nature of their topic, opening the book with a short account of a few common verbs for copulation, a bit of Biblical laying of hands on testes, and a glorious plate of a 16th century painting of Adam and Eve. This is typical, this scattering of erudition, delightful connections and impudent comments.

It is evident that the authors have little need for religion. Potts is no stranger to controversy, having served for several years as the outspoken head of Family Health International, promoting contraception and working to slow AIDS in the developing world. He has had his share of run-ins with religious and political opponents, and he makes no secret of his moral and political views on sexuality. That he treats much of the sociopolitical realm as needful of rationality and scientific insight is no surprise. It is not, however, simplistic one-ought-to moral reasoning. More often, the biological details are served up to show how simple cultural traditions or religious absolutes are inadequate for understanding the nature of our tendencies and behaviors.

There is a long tradition of writing about biological reasons for the peculiarities of sexual behavior, predating its obvious antecedents in modern sociobiological literature. Well before Darwin, the animal nature of sex and the sexual nature of animals fascinated scientific naturalists and the public alike. It was Darwin who jolted the connection beyond analogy into more immediacy for the explanation of our behavior. Although he waited for others to open the controversy of human origins after his Origin of Species (1859), his rather belated entry into the explanation of human evolution was radical. In its very title, The Descent of Man, and Selection in Relation to Sex (1871), Darwin centered the nature of humanity on sexual choices and interactions and illustrated his theoretical arguments with examples from stag beetle wrestling bouts to gorgeous peacock tails. If it was humbling to be seen as an ape, how more demoralizing—in two senses of the word—could it be to see Love and Beauty as blind consequences of the struggle for existence.

Perhaps it was too radical, for little in the way of a research program followed Darwin. Discussions of human nature certainly turned toward biology, but the heredity of difference flourished first (with eugenics and then genetics). In this century, Freud's biological vision of the mind captured the discussion of sexuality. The primitive animal past operated deeply within us, as an encapsulated, generic instinct of sexual drive. Sex was less interesting for itself, seen rather as the key to the manifestation of complicated, derived behaviors.

Starting in the 1950s, and reaching a crescendo in the heady sociobiological theorizing of the 1970s, behavioral biologists sought to dethrone this treatment of sexuality. Under the neo-Darwinian banner of the population genetics of individual advantage, they created models that explained complicated animal behaviors as the more direct operation of strategies for genetic success. The robustness of theories of relative contributions, investments, strategies and contests could easily be seen in the clarity they brought to accounts of sexual behaviors. Sex is, after all, among the most elaborate of things that animals do and one of the most fascinating to us. Darwinian models made sense of it. At the same time, popularizing has flourished, from Desmond Morris's best-selling The Naked Ape: A Zoologist's Study of the Human Animal (1967) to David Barash and Judith Lipton's Making Sense of Sex: How Genes and Gender Influence our Relationships (1997). Potts and Short could have too easily given us no more than a number of glib adaptive stories or tales of our genes making us do it. That they take more account of social causation in an entertaining read packed with good information makes this book one of the best of the lot.

In one important way, Potts and Short have extended this sense making beyond the usual popular accounts of sex differences and sexual strategies. Fully half of the book deals with what might better be called the biology of family, encompassing nursing, maturing, domestic violence, sexual morality and dual standards, sexually transmitted disease and reproductive rates in an overpopulated world. The text crackles with their provocative statements, leaving no guesses where their morality and politics lie, nor their intense concern with social problems related to sexuality and reproduction. It's an unwavering commitment, throughout the book, to an Enlightenment ideal of rationalist, scientific pursuit of intellectual understanding as the road to social betterment.