American Scientist

Origins of the Social Mind: Evolutionary Psychology and Child Development. Edited by Bruce J. Ellis and David F. Bjorklund. xviii + 540 pp. Guilford Press, 2005. $65.

Fifteen years ago, the application of principles of evolutionary biology to psychology was still new and unfamiliar to most psychologists. That changed with the publication in 1992 of The Adapted Mind (edited by Jerome Barkow, Leda Cosmides and John Tooby), which established evolutionary psychology as a progressive research program. Evolutionary psychologists take the view that "human nature" is a collection of specialized psychological mechanisms that proved beneficial in our ancestral environment.

Today, evolutionary developmental psychology is as new and unfamiliar as evolutionary psychology was 15 years ago. Bruce J. Ellis and David F. Bjorklund, the editors of a new book on the subject, Origins of the Social Mind, see this new subfield not simply as an expansion of evolutionary psychology into the developmental realm, but as an integration of developmental and evolutionary thinking. They came to this intersection from different directions: Ellis trained with David Buss, a noted evolutionary social psychologist, and then turned to consider developmental questions, whereas Bjorklund started out as a developmental psychologist, became a well-known expert in cognitive development and then incorporated an evolutionary perspective in his work.

Unlike most other subfields of psychology, which typically focus on particular phenomena (cognitive psychologists study cognition, social psychologists study social processes, and so on), developmental psychology and evolutionary psychology do not have separate domains. Rather, they represent different approaches to the study of all psychological phenomena. Cognitive processes, for example, can be investigated from a developmental perspective (as in the work of Jean Piaget) or from an evolutionary one (as in the work of Cosmides and Tooby). Integrating the two viewpoints is easier said than done. Developmental psychologists, who study how behavior and cognition change with age, focus on ontogeny, the development of the individual. In contrast, evolutionary psychologists focus on phylogeny, the development of the species.

Furthermore, developmental psychologists concentrate on proximate causes—how biological and environmental factors interact to influence behavior over the life of the individual. In contrast, evolutionary psychologists focus on ultimate causes—the reasons that certain behaviors were selected for over the history of the species—and explain behavior with reference to its function in the distant past. Evolutionary developmental psychologists need to consider both proximate and ultimate causes.

With few exceptions (such as John Bowlby's hypothesis that specialized psychological mechanisms have evolved for  forming strong emotional attachments between caregivers and infants, and Jay Belsky's argument that a child's early family environment provides cues as to which reproductive strategy will be most adaptive in adolescence and adulthood), mainstream developmental psychology has not been very informed by evolutionary theory. And evolutionary psychologists have often limited themselves to the study of adults, thus missing out on developmental psychology. A major step toward a rapprochement was the publication in 2002 of The Origins of Human Nature: Evolutionary Developmental Psychology, by Bjorklund and Anthony D. Pellegrini.

Origins of the Social Mind takes another step in that direction, assembling a critical mass of authors who have both developmental and evolutionary interests. The book consists of 19 contributed chapters, organized into three sections—on general theoretical issues, personality and social development, and cognitive development. The text is long (more than 500 pages) and written in a technical style with lots of citations. Definitely pitched for an academic audience, this is not a book that people outside psychology are likely to pick up and read cover-to-cover for fun. For an accessible introduction to evolutionary developmental psychology, The Origins of Human Nature is a better bet.

The editors try to tie Origins of the Social Mind together by providing a nice introductory chapter, an index and some references within chapters to other chapters. However, the chapters really vary in content and approach, reflecting the fact that evolutionary developmental psychology is still coalescing as a research program. Some of them are rather rambling reviews of developmental research in a particular area, with evolutionary speculations sprinkled on top. These chapters, in which existing developmental data are reinterpreted in the light of evolutionary theory, may provide useful references for people already interested in those areas of research, but they don't always make fascinating reading. The more successful chapters are organized around an argument rather than an area of study, venturing a provocative hypothesis and presenting new research designed to test it.

In one such chapter, Jay Belsky describes his "differential susceptibility hypothesis"—that is, the idea that children vary in their responsiveness to early environmental influences such as parenting. Belsky offers an evolutionary argument for why such variation would be adaptive, and he provides some empirical evidence in support, including some new analyses of the data set of the National Institute of Child Health and Human Development Study of Early Child Care.

In another interesting chapter, Jesse M. Bering argues that religious beliefs may be prevalent because they are adaptive, in that they promote prosocial behavior—that is, they provide a motivation to behave well even when no other person is looking: because God or some other supernatural agent may be watching. [Editor's note: See feature article by Bering in this issue.] Bering suggests that evolved psychological mechanisms account for people's tendency to attribute coincidences to supernatural agency, and he presents new developmental data consistent with this hypothesis.

In a chapter on empathizing, Simon Baron-Cohen summarizes evidence in favor of his "extreme male brain" theory of autism (a "male brain" being one in which systemizing is more developed than empathizing). The evolutionary argument for sexual variation in brain types is only sketched here; it is discussed at greater length in his 2003 book The Essential Difference: The Truth about the Male and Female Brain.

Among the weaker contributions, a chapter by Glenn E. Weisfeld and Heather C. Janisse illustrates the sort of Panglossian thinking (assuming that every characteristic is adaptive) for which evolutionary psychology is sometimes criticized. Weisfeld and Janisse even suggest that male nipples—the classic example of a biological spandrel, or evolutionary by-product (in this case, of female nipples)—"may function to attract or reassure infants" (no evidence for this claim is provided). They also make a number of other dubious claims, such as this one: "Before puberty, the sexes are quite similar." It's hard to believe that anyone who has spent time around children would say such a thing, and it is directly contradicted by data discussed in other chapters. However, Weisfeld and Janisse don't have a monopoly on dubious claims. In his chapter, Brian MacWhinney suggests that "individuals with high levels of imitative skill are likely to attract mates by entrancing their attention" (again, no evidence is provided). Imitating a prospective mate is sexy? Maybe, but I'm not going to try it on my next date.

One of the most interesting questions for evolutionary developmental psychology is whether childhood itself is an adaptation: Is the extended period of psychological immaturity in humans just an inevitable by-product of the fact that it takes us a long time to reach adulthood, or is it actually more beneficial than a faster rate of development would be? This issue is addressed in several chapters, especially one by Mark V. Flinn and Carol V. Ward and another by Bjorklund and Justin S. Rosenberg. These authors acknowledge that there are some biological constraints on the system (for example, fetal brain size versus female hip width) but argue that an extended childhood is actually adaptive, because it allows time to develop the social-cognitive skills necessary to master the specifics of children's social environments. However, their argument assumes that ancestral social environments were varied enough for a "tuning" period to be beneficial and that a slower rate of social-cognitive development was selected over faster alternatives. It might just be that children develop as fast as is biologically possible. Such questions should keep evolutionary developmental psychologists busy for a while.

So has an evolutionary perspective taken over developmental psychology? Certainly not yet. A look at the indexes for the programs from the last three biennial meetings of the Society for Research in Child Development (the leading professional organization for developmental psychologists) turns up only a couple of items pertaining to evolution. Will the evolutionary perspective become dominant within developmental psychology eventually? I wouldn't bet against it, for the same reason I wouldn't bet against evolutionary psychology in general—a lack of alternatives. Evolutionary psychology has a lot of problems—claims that run ahead of the evidence, misunderstandings and oversimplifications of evolutionary biology, and the perception that the approach provides scientific cover for stereotypical attitudes toward the sexes. Nevertheless, it continues to attract adherents and is arguably the most progressive paradigm in psychology today. (It just goes to show that, in science, relative promise can be more important than current evidence.) Evolutionary psychology has the potential to unify our understanding of psychological phenomena under one theoretical umbrella and faces little competition for that role.

The only contender of similar scope is developmental systems theory, which argues that adult structure is not encoded in the genes but rather emerges through the interaction of each organism with its environment. Developmental systems theorists criticize evolutionary psychology's model of development—that genes determine the range of options from which environment selects (the "jukebox" metaphor)—as overly deterministic. However, developmental systems theory can be criticized as not deterministic enough. By emphasizing the unique complexity of every individual, the theory risks reducing psychology to biography. Some generalization and simplification are necessary for a theory to gain predictive purchase. In any event, Bjorklund argues that answers to the developmental systems theorists' critiques can be incorporated into the framework of evolutionary psychology.

Evolutionary developmental biology, or "evo devo," is currently a hot topic in biology. Fifteen years from now, we may look back on the publication of Origins of the Social Mind as the point when evo devo became a hot topic in psychology.