Kevin MacDonald, Ph.D.

CSULB, Department of Psychology

A New Paradigm for Evolutionary Psychology: The Centrality of Domain-General Mechanisms for Conceptualizing Human Adaptation

Reviewed by Kevin MacDonald

Human sexual behavior has become the centerpiece of the evolutionary analysis of human behavior at least partly because there is a very rich theoretical basis stemming from Trivers's (1972) seminal article on parental investment. In stark contrast to other social science perspectives, this theoretical base has provided evolutionists with the ability to make predictions regarding human behavior, and the result has been dozens of empirical studies that essentially confirm the utility of this approach.

Given the overwhelming success of the evolutionary perspective in this area, it is tempting to suppose that little remains to be done. However, reading this book made me realize how badly a scholarly book in this area was needed. This is first and foremost an excellent book'a must-read both for specialists in the area of sexual behavior as well as people interested in evolutionary psychology generally. Throughout the volume the reader is provided with highly detailed, nuanced presentations rather than superficial summaries. Particularly noteworthy in this regard are Chapters 2 and 3 that cover the theory of sexual selection and the data from animals. Many of those doing research on humans from an evolutionary perspective are not familiar with the details of this literature, and the typical examples appearing in popularized treatments fail to convey the subtlety and variation that is actually out there. Geary has covered this literature in an authoritative manner. He has not relied on summary statements or thumbnail sketches or on widely known examples like elephant seals and peafowl, but has delved deeply into the original literature and the result is an awareness of the complexity and subtlety of the issues.

By the nature of their interests, evolutionists are forced to become familiar with literatures in evolutionary biology, neuropsychology and genetics, anthropology, and psychology. Geary is up to the task. Chapters 4 and 5 on paternal investment and sexual selection in contemporary humans are cases in point. There are discussions of general theoretical issues grounded in evolutionary biology, primate patterns, the cross-cultural data gleaned from anthropological accounts, the social regulation of sexual behavior in historical Western societies that has resulted in socially imposed monogamy, neurophysiological mechanisms, and individual differences revealed by psychological research in contemporary Western societies. His emphasis on the developmental literature and his attention to individual differences are often lacking in treatments by evolutionists. Particularly welcome is the chapter on paternal investment. Paternal provision of resources has a clear effect on offspring survival in many pre-industrial societies, but even in contemporary developed societies, Geary concludes that "children living in stable social and home environments and with both biological parents appear to be in better health and apparently enjoy a longer life span, on average, than children living in other situations" (pp. 113-114). Because many children abandoned by their biological father do survive, however, Geary concludes that over evolutionary time paternal investment resulted in a conditional rather than an absolute benefit to children. The conditional importance of paternal investment then sets the stage for the complex dynamics of sexual selection in humans.

This book is far more than an exhaustive review of the literature, but chock-full of insights and original ideas. Indeed, Geary's main contribution really amounts to a powerful new paradigm for conceptualizing evolutionary psychology. Geary's starting point is the idea that there is a fundamental goal of controlling social, biological, and physical resources that support survival and reproduction. For example, males and females evolved very different strategies for controlling reproductive resources, including a greater interest in social dominance issues in the case of men and placing a higher value on reciprocal social relationships in the case of women. Geary also posits emotional mechanisms that support and direct strategies aimed at acquiring resources. Examples are attributional mechanisms that allow people to interpret failure as due to external causes and fantasy mechanisms that allow people to rehearse desired scenarios in a manner that would reduce the difference between fantasized and actual outcomes in the real world.

These motivational and emotional mechanisms are critical for the proper functioning of evolved social, biological, and physical modules, all of which presuppose evolved cognitive systems. Geary reviews the controversy over domain-specific versus domain-general mechanisms in psychology, and concludes that both types of systems are important. Some systems are domain-specific and have a modular architecture (e.g., song learning in birds), but other systems are domain-general, such as the prefrontal cortex which regulates a variety of more specific systems. Domain-specific systems are contextually sensitive: "Evolved systems do not result in fixed systems of behavior that reflexively respond to environmental contingencies but rather are designed to produce behavioral and cognitive variability" (p. 199) so that people can respond adaptively to situational demands. Based on Ernst Mayr's work and much research in child development, Geary distinguishes between open genetic systems and closed genetic systems, the latter impervious to environmental influences while the former represent a sort of "skeletal knowledge" where domain-relevant experience during development (e.g., social play) is required for full adult competence. Children are programmed to seek out such domain-relevant experience by seeking out novel or highly stimulating environments (e.g., rough and tumble play) and rehearsing social scripts (e.g., playing 'mommy'). Nevertheless, while there is a great deal of inborn structure to the cognitive modules underlying behavior, Geary rejects the view that human behavior is reflexively driven by such modules in response to their eliciting environments. Here Geary emphasizes the modulating effects of belief systems, a phenomenon that is presumably unique to humans.

Geary distinguishes between two types of open genetic programs. One is exemplified by language learning where the genetic program codes for a finite list of possibilities and experience during a sensitive period activates or deactivates subsets of the possibilities. Such a program is relatively closed compared to the other type of open genetic program which is exemplified by biological modules where there is no preset finite list of possible flora and fauna. In this case the open genetic program biases the processing of domain-relevant information and influences the categorization processes. However, extensive experience is required to develop the sophisticated knowledge that humans are able to develop. This latter type of cognitive model is quite common, and Geary proposes that one function of the prolonged pre-adult stage of humans is to allow the development of adult competencies adapted to local conditions from the set of skeletal open genetic programs.

With very few exceptions, evolutionary psychologists have tended to focus exclusively on domain-specific mechanisms viewed as adaptations designed to solve recurrent problems in the the environment of evolutionary adaptedness (EEA). Geary goes beyond this very restricted paradigm to discuss sex differences in evolutionarily novel domains, particularly domains that rely on domain-general mechanisms like general intelligence (g). As Geary notes, high intelligence is an advantage in novel, complex, constantly changing environments where people must attend to a multiplicity of tasks and where learning new skills has great payoffs. As such, general intelligence is the very antithesis of an adaptation narrowly defined as a solution to a specific recurrent adaptive problem in the EEA. Rather general intelligence is a domain-general adaptation that evolved to deal with a general class of problems, the need to cope effectively with novel (non-recurrent) ecological conditions and some aspects of human social interaction. Regarding the relationship between general intelligence and human social interaction, Geary notes that while not all social skills are related to g, g is correlated with skill at negotiating complex social environments such as those present in contemporary business and professional contexts.

Geary proposes that g, which includes abilities such as speed of information processing and working memory, "reflects the ability to use evolved, or biologically primary, cognitive competencies in ways that are unrelated to their evolutionary function" (p. 308). An example is reading which uses many of the same primary (domain-specific) adaptations involved in language comprehension and production to perform the non-evolved, biologically secondary task of reading. Individual differences in reading abilty are correlated with g and reflect the ease with which children can adapt their evolved systems to accomplish a novel task. Unlike spoken vocabulary which develops rapidly and effortlessly'a defining feature of a domain-specific adaptation, reading develops slowly and with effort, and it is facilitated by g as a domain-general evolved mechanism.

Geary's treatment is a much needed antidote to the exclusive emphasis on domain-specific mechanisms so common among evolutionary psychologists. In this new paradigm, domain-general mechanisms assume their rightful place at the very center of evolutionary psychology. Geary notes that people with relatively high general intelligence are viewed as a valued resource in mate-choice in cultures around the world, indicating that individual differences in g have been a critical resource in sexual selection and human mate choice. Moreover, reading, writing, and other evolutionarily novel skills such as solving mathematical problems turn out to be very important in attaining social status in contemporary and many historical societies. It is noteworthy that at least until very recently social status has been highly correlated with reproductive success in traditional human societies'a phenomenon that has undoubtedly resulted in a eugenic effect at least until very recently in human evolution (Lynn, 1997). General intelligence has therefore been a critical component of human adaptation, and individual differences in g have been a very salient feature of the human mating landscape.

Geary rejects the proposal that males have a higher g than females. Although some commonly used subtests of intelligence do show sex differences, pure measures of g do not show a sex difference, and Geary argues that the sex differences that have been found are most likely the result of sex differences in biologically primary domain-specific systems. However, there are also a variety of important sex differences in secondary adaptations, such as sex differences in some areas of mathematics favoring boys and sex differences in some areas of language processing favoring girls. In Geary's view, these sex differences stem from evolved sex differences in primary adaptations such as those involving three-dimensional spatial abilities required for navigation in the EEA, but utilized now in the service of the biologically secondary task of solving algebraic word problems. Sex differences in average ability in these primary abilities are important for occupational attainment in contemporary societies. For example, 3 out of 5 boys outscore the average girl in mathematics achievement in samples from the general population. Because of greater variability among males, for gifted samples the ratio is as high as 13:1 for adolescents, and 19:1 for those taking the mathematics portion of the Scholastic Aptitude Test in high school.

However, interest in math-intensive careers tends to be lower even among women who have sufficient mathematical ability to succeed in such careers, a finding that Geary attributes indirectly to sexual selection. Females, to a greater extent than males, are attracted to careers involving intimate and reciprocal social relationships and animate objects (e.g., biology, medicine) rather than inanimate objects (e.g., physics, engineering). Thus "the sex differences in occupational pursuits are a reflection, at least in part, of the the different reproductive motives, such as status striving and interest in people, of men and women" (p. 329).

Male andFemale: The Evolution of Human Sex Differences is a mature work of great depth and breadth. Its greatest strength is the manner in which it unifes the findings from evolutionary biology, cognitive science, developmental psychology, neuroscience, individual differences, behavior genetics, and ethology. This makes it especially welcome as a publication of the American Psychological Association, since much work remains to be done to convince a great many psychologists of the value of an evolutionary perspective. But I hope that it will also have a broadening influence on those already converted to the evolutionary paradigm, many of whom remain wedded to simplistic paradigms with an exclusive emphasis on domain-specific systems that are unable to encompass the complexity of human behavior. Without such an integrating, rather than isolating focus, evolutionary psychology will have only limited impact and will appear at best as a sterile specializtion, and at worst as a scientific cult, within the broad scope of the behavioral and brain sciences.

References

Lynn, R., 1997. Dysgenics: Genetic Deterioration in Modern Populations. Westport, CT: Praeger.

Trivers, R. L. (1972). Parental investment and sexual selection. In B. Campbell (Ed.), Sexual Selection and the Descent of Man 1871-1971 (pp. 136-179). Chicago: Aldine.