Anne Fausto-SterlingNO
Beyond Difference:
A Biologist's Perspective
Do biologists know things of use to social scientists who study gender? Answering this question requires a bit of context. During the past few years we have been subjected to a series of blows, both within the academy and without. The left hook hits us from the media. Lead stories in Time (August 15, 1994), Newsweek (March 27,1995; June 3, 1996), and The New Republic (Wright, 1994a) (to name but a few) tell us that infidelity and physical desire are both in our genes, that feminists have hopelessly misled their flock by attacking the first wave of sociobiological claims about gender and social change, and that differences in brain anatomy might "explain why women are more intuitive" (Newsweek, 1995, p. 54)....
The popular media's publicity blitz describes the encroachment of biological understandings on arenas of social behavior previously seen to be the bailiwick of the social sciences. Some reporters and scientists present these new biological understandings as certain beyond question. To be sure, according to this view, some gaps in our knowledge remain, but the current wave of findings has solidified the biological framework on which we hang our understandings of sex differences. Shouldn't we be happy to have these vexing questions settled once and for all? ...
What tools can I, as a biologist, offer to social scientists wishing to understand the thought currents of the past few years? What can biology tell us about human sex differences? My quarrels with many of the arguments about innate human differences and their evolution stem from understandings of the nature of biological explanation, which differ significantly from those of writers such as [journalist Robert] Wright, [J. Richard] Udry, and the various Time and Newsweek authors. The biological work to which I am drawn contains solid theory and detailed empirical information; using such work as a starting point enables us to build complex, interesting accounts of behavior....
Why Frogs Jump
I'll start with a seemingly simple question: "Why does a frog jump?" The answer can be given at several different levels. Within the moment of watching the frog jump, we can suggest a holistic answer-the frog jumps as part of an ecosystem. It senses a predator nearby and gets out of the way. A more mechanistic, reductionist approach would focus on the frog's leg muscles: it jumps because its muscles twitch. Even more specifically, we can reduce the level of explanation to a discussion of how and why muscles twitch, and we can say it's jumping because two proteins, actin and myosin, have molecular properties that allow them to contract, something they do in response to a nerve impulse. Each of these levels of explanation is valid for particular purposes, but one cannot necessarily substitute for the other....
Focusing on either the contemporary ecosystem or adult muscle function leaves out two important types of biological analysis and explanation-development (embryological, juvenile, and adult) and evolution. Both mechanistic and holistic analyses of current behaviors describe what is. In contrast, examining individual development or species evolution allows us to talk about how things get to be the way they are....
Evolutionists ... describe events that take place over many generations. An evolutionist would speak in terms of genetic variation, natural selection, adaptation, and geographic isolation (to name the most commonly studied mechanisms of evolution)....
Developmental answers respond to the "why" question for individual frogs within a particular generation, while evolutionists look at changes in gene frequency at the population level. Suppose I ask why two groups of frogs jump differently. Why, for example, do bullfrogs jump further than leopard frogs? One can stick with a strictly reductionist explanation. On average, bullfrogs jump further because they are a lot bigger. And one could reduce that answer to details about the number of muscle fibers and the comparative biophysics of fibers of different lengths and thicknesses. But one could add in a second question: why are bullfrogs larger than leopard frogs? One answer might be development-they are bigger because bullfrogs spend two years as tadpoles and thus have a much longer growing period than leopard frogs, which metamorphose in a single growing season. Both explanations are valid, but offer different kinds of information. One could push matters further, asking why the bullfrog life cycle differs from that of the leopard frog. An answer here would require data about the evolution of the two species. When and under what circumstances did they diverge from a common ancestor? What kind of life cycle did the progenitor species have, i.e., did leopard frogs lose a year of development or did bullfrogs gain one? And why? Was it due to natural selection, geographical isolation or genetic drift? Or, does each species even now exhibit developmental plasticity-the ability to change its life cycle in appropriate environmental circumstances? Answers to these questions can be acquired empirically. Indeed, solving problems such as these is what many evolutionary biologists do for a living. It will not do simply to assume the answer.
Many social scientists study gender inequity. Some hope to figure out how to equalize difference. Others believe that whatever differences they've observed cannot (and perhaps should not) change. Each of these groups has an underlying and not always articulated theory about the biological basis of difference; when pressed, they will invoke it to their advantage. But when dueling social scientists use biological tools to do battle, they do not always think clearly about the level and type of biological explanation with which they argue.
Thus the first thing social scientists need to think through when they use biology to ask the difference question is for which level of explanation do they seek an answer. Such a question is neither innocent nor far-removed from questions of policy. If one finds a sex difference, does it help to know its immediate physiological cause, or does one really seek a developmental or even an evolutionary explanation? I assume that in a trivial sense anything we do has an immediate physiological cause, i.e., if I run from danger, it is not only because I can recognize the cultural signs of a dangerous situation. It is also because I am physically able to see, hear, and run, in the same way that a frog can jump because of the actin and myosin in its muscles. But that knowledge is not particularly interesting if what we want to understand is why I consider a particular situation to be dangerous in the first place. The answer to such a question depends very much on why one wants to study difference in the first place. Does one want to learn about it in order to explain the way things are, or to design policies to change the status quo? I suggest that currently available types of evolutionary explanations work best in the former case, whereas developmental understandings are most useful in the latter. As the following discussion makes plain, understandings at the level of molecular physiology are usually the least useful for a researcher interested in designing effective social policy.
From Mice to Bats and Beyond
Geneticists look at evolution in a number of different ways. The following discussion comes from the work of C.H. Waddington (1975). Animal populations consist of individuals with unique genotypes-the sum of all the genes in a cell. During any particular generation, populations participate in different kinds of systems. Waddington named one of these "the exploitative system." Animals, within the limits of their genetic makeup (e.g., mice can't fly from one tree top to the next; to colonize tree tops they must climb or jump to nearby branches), choose among and modify possible environments, thus creating an environmental niche. At the same time, animals in any particular generation develop under particular stresses and strains. Waddington called this development within a single generation "the epigenetic system." During development, a chance environmental stress might reveal a developmental potential not ordinarily visible. Suppose, for example, our hypothetical tree mice hadn't found much food during a particular year. Some females might go through pregnancy in a condition of near starvation. As a result of that, some fetuses would die, others would develop normally, and still others might survive but exhibit some sort of limb defects, say a failure of the skin connecting the limb digits to degenerate during development as it normally does. Perhaps these abnormalitiesshow up only when a particular genotype develops in combination with low protein availability. The result: webbed feet. (Such a scenario is not particularly far-fetched. Rats subjected to prenatal heat stress, for example, developed longer limbs.) (Siegel, Doyle & Kelley, 1977)
Webbed feet might make mice slow climbers, rendering them more vulnerable to predation by a passing hawk.... But that disadvantage might be balanced out by an emerging ability-the webbed feet enable the mouse to glide when jumping from tree to tree, thereby avoiding birds in the habit of scanning tree trunks for passing mice, and increasing their food options by enabling them to reach more distant tree tops. The mouse-hawk interactions and the ability to improve survival by niche extension form part of what Waddington called "the natural selective system." If the environmental stress of low food availability remained for several generations, mice with an epigenetic system (i.e., an interaction between environment and genes to produce a new phenotype) in which development during protein deprivation produced webbed feet, might survive with higher frequency than that of same genotype developing under high food conditions. (Note how the same genotype can produce different phenotypes under different developmental conditions.) Thus the low protein-webbed feet epigenetic system would become more frequent in future generations. If the selection went on for long enough, these mice might even develop a new niche, forgoing climbing altogether. Waddington demonstrated that in some cases, new phenotypes induced by epigenetic stresses stabilize even if the original stress disappears (Waddington, 1975). Thus a new variety of webbed-footed gliding mouse might emerge and, with further selection for more efficient gliding, might even evolve into what is called in German a fledermaus, a flying mouse, or bat. I do not suggest that this is how bats actually evolved; I have merely created a plausible scenario in order to illustrate the varied biological systems involved in evolution.
Using Waddington's framework, let's turn to some of the modern-day theorizing about the evolution of the human psyche. Robert Wright (1994b) champions a new group of academics that call themselves evolutionary psychologists. In 1992, Barkow, Cosmides and Tooby published The Adapted Mind, arguably the scholarly founding volume for this emerging field. Their central premise is that "there is a universal human nature, but that this universality exists primarily at the level of evolved psychological mechanisms, not of expressed cultural behaviors" (p. 5). They also postulate that psychological mechanisms evolved as adaptations via natural selection and "that the evolved structure of the human mind is adapted to the way of life of Pleistocene huntergatherers.... " (p. 5). These academics argue that we can only understand contemporary human psychology by understanding how the mind evolved.
Some evolutionary psychologists have a lot to say about sex and gender. Recently, David Buss (1995), a prominent evolutionary psychologist, discussed the natural selective system faced by primitive humans:
Women face the problem of securing a reliable or replenishable supply of resources to carry them through pregnancy, and lactation.... especially when food resources were scarce, that is, during droughts or harsh winters. All people are descendants of a long and unbroken line of women who successively solved this adaptive challenge; for example, by preferring mates who show the ability to accrue resources and to share them. (p. 164)
Buss tells a story of much the same quality as the one I just invented about the evolution of bats. It has a certain plausibility. Proto-human females must, indeed, have had the challenge of finding enough nutrition to sustain pregnancy and lactation. But as does my bat tale, Buss's lacks essential information. Without knowing when the traits of interest became a permanent part of the human lineage, we can know little about the actual environmental variations, little about the degree to which nutritional needs, via an epigenetic system, might have sharpened foraging abilities dormant within some of the genotypes in particular populations, and/or whether systems of natural selection worked to make food utilization more physiologically efficient. If Buss's selective scenario played out, perhaps it fueled the development of foraging skills, including the ability to hold three-dimensional maps in one's mind's eye-returning even after many years, to a spot which had previously contained a good food source. Certainly Buss can hypothesize that pregnancy and lactation led females to select males who were good providers, just as I can hypothesize that it led females to evolve well-developed spatial and memory skills. We might both be wrong, or right, but without more data and a far more specific hypothesis, we have no way of knowing.
There are a lot of data about prehistoric human culture and protohominids, and it is appropriate to use them to devise hypotheses about human evolution. It is not unreasonable to ask the hypothesis-builders of evolutionary psychology to at least postulate at what point in human or hominid history they imagine contemporary reproductive behaviors to have first appeared. "Throughout the Pleistocene" is pretty vague. What is the evidence that it wasn't earlier or later? What, if any, animal systems provide unnamed models? What were the food and predator stresses at that moment? Data on these points can be gleaned from the archeological and geological record. How did humans respond? Biogeographic data can be brought to bear on this point. Was there a division of labor during this early period of evolution? Or did gender-based divisions of labor evolve later (Leibowitz, 1978)?
Over how long a period of time did human mating systems evolve? Or are they still evolving? For example, the earliest humans living in the heart of Africa certainly did not, as Buss suggests, experience harsh winters. How do the events of interest to evolutionary psychology relate in time to the expansion and geographical radiation of human populations? What evidence is there for a long, unbroken line of women? When and where were there genetic bottlenecks during the course of human evolution? How many of them were there? The use of molecular evidence to trace human evolution has created a great deal of ferment during recent years (Ayala, 1995; Culotta, 1995; Dorit, Akashi & Gilbert, 1995; Gibbons, 1994, 1995, 1996; Hammer, 1995; Piazza, 1993; Tishkoff et al., 1996). It would be nice if evolutionary psychologists were specifically to incorporate this new information into their theory building. Which evolutionary lines or kinds of adaptive behavior were lost or selected for? How much of our current gene pool do we have because of genetic drift or geographic isolation, how much because of adaptation and natural selection? Some prior work at least attempts to situate theory-making within a time line and a set of postulates about which organisms (chimps? bonobos? Australopithecus? Homo habilis?) evolved modern human mating patterns (Leibowitz, 1978; Tanner, 1981; Fedigan, 1986). Let's engage in current discussions using the best available knowledge base and the most highly detailed hypotheses available.
Without addressing some of these questions, evaluating hypotheses becomes very difficult. For example, given how precarious early human existence must have been, isn't it possible that females realized that no individual male would live long enough or stay healthy enough to provide over a period of years for his offspring? Isn't it just as likely then that the females who passed on more genes to the next generation were the ones who hedged their bets and slept with more than one male? Buss and other evolutionary psychologists engage in what are, in essence, thought-experiments, but unless much more carefully specified hypotheses are presented, there's no way to know how the postulated startingpoints relate to the actual starting-points.
The development of scientifically sound theories about the evolution of human behavioral patterns and their relationship to contemporary behavior could emerge from collaborations between social scientists, evolutionists, and behavioral biologists. Specifically, those experts in the social studies of science who have been so bitterly attacked in the current science wars have a great deal to offer. One model collaboration, developed in the halcyon days before science studies were taken seriously enough to be attacked, is a paper written by Bruno Latour (Mr. Science Studies!! See Latour, 1987) and Sharon Strum (Strum, 1987), a primatologist who studies baboon behavior. Latour and Strum (1986) devised a set of questions aimed at making specific hypotheses about human evolution. Using their questionnaire, they evaluated the quality of the theories constructed by both social scientists and biologists. (All failed the test pretty miserably.) I urge anyone devising theories about evolution and human behavior to use Latour and Strum's nine questions [Table 1] to measure the scientific quality of their hypotheses. As Latour and Strum conclude, "the difficulties of tracing human social origins goes beyond the mere speculative nature of the endeavor. Scientists have not yet come to terms with what makes an account scientific or convincing ... when scientists are unaware of the mythic character and function of origin accounts ... the coherence of the scientific account suffers" (p. 186).