We humans are retarded apes. With this retardation comes the flexibility and ability to adapt to new situations because our brains are not hard-wired until late in life, monkey time, as a result of our DNA, which diverged from our primate ancestors. This is one of the convincing arguments put forth by the authors in integrating the seemingly parallel if not divergent fields of evolutionary psychology and developmental psychology.

Simply put, evolutionary psychology views the ontogeny of the human mind as an unfolding process of the genes with time, while developmental psychology sees it mainly as an epigenetic interaction between a tabula rasa of mind and environment. Evolutionary developmental psychology attempts to integrate the seemingly contradictory views by postulating that what is inherited is a gene-environment system in which genes unfold, the environment selectively turns on and off certain genes, and, importantly, genes also choose their own conducive environment. Genes determine individuals who create or seek out environments that are conducive to their phenotypic expression, thus passing on to the succeeding generations a system of gene-environment.

Evolutionary developmental psychology generally accepts the notion that the human mind consists of domain-specific modules (e.g., cognition, language, mathematics) that have evolved in the species. "What infants come into the world with are processing biases and constraints—products of natural selection—that serve as the foundation for developing a human mind" (p. 191). The authors contend that there is an evolutionary rationale for certain child-specific deficiencies, such as a tendency for 3–4-year-olds to overestimate their imitative ability and the degree of overestimation (inaccuracy) to correlate with their IQ. "As a result, bright young children continue to experiment with new behaviors and practice old ones, improving their skills at a time when trial-and-error learning is so important." They also caution against attempts to introduce formal education earlier in childhood, when the brain might not be prepared for it.

Evolutionary developmental psychology proposes that human infants have evolved psychological structures that are optimized for age-appropriate learning in a co-evolved milieu and that family relationships (e.g., parent-child, sibling, kin) are also products of evolution. From the perspective of parental genes, not all offspring have an equal chance of further propagation, necessitating differential investment of resources. From the perspective of genes of siblings, competition for such resources for the individual’s survival and reproduction is of paramount importance. Parental investment theory explains the evolution of sex differences in behavior. The amount of investment of resources (both psychological and biological) of mammals for seeking a mate versus parenting differs according to sex, which is seen to underlie such behavioral differences as what is desirable in a mate (for males, the female’s genetic fitness; for females, the male’s ability to provide resources). Women are more emotionally expressive than men but can also inhibit or control emotional expression better than men. This is attributed to the fact that females who could control or hide their sexual arousal to males other than their spouses and/or who could inhibit their aggressive emotions toward their infants may have had an evolutionary advantage. Parental investment theory also explains the greater likelihood (two to 10 times) of parental abuse of children with congenital defects. There is competition for resources between children and parents as well; therefore, the rate of infanticide is higher among younger than older women because the chances for later reproduction are greater at a younger age. Stepparents naturally invest fewer resources in stepchildren than in biological offspring and tend to abuse their stepchildren more often both in fact and in fairy tales (e.g., Cinderella). Parental investment theory also explains risk-taking and risk-aversive behavior in males—males who are more involved in child care would be risk aversive, and females who have evolved to be caregivers are, in general, risk aversive. The grandmother hypothesis posits that there is survival advantage for older females to participate in nurturing the grandchildren, which will result in their daughters being able to reproduce more, which also selects for longevity among women.

Fitness for successful competition for resources forms the basis for explaining several behaviors in human development, including attachment, dominance, aggression (in females, there is more "relational aggression," i.e., exclusion from the group, rather than direct aggression), and social behavior. The last chapter of the book, "Homo Ludens" (playful man), is an interesting study of the function of play in human development. Here the authors propose that play has age-specific functions in adaptive neural formation and is not just a practice run for adult behavior. An important point they make in the epilogue is that evolved mechanisms are not necessarily adaptive for people today. "Much of what we teach in school is ‘natural’ in that teaching involves tasks never encountered by our ancestors, and some ‘normal’ individual differences in behaviors (e.g., high levels of activity) may be especially maladaptive in contemporary environments."

The Origins of Human Nature is an ambitious, well-researched, comprehensive, and well-written (if a bit recursive) book that presents evolutionary developmental psychology as an attractive integration. I find an evolutionary perspective essential in understanding the whys of things, from stupid design features of the human body (e.g., why the airway crosses the digestive tract) to functions of emotions and their dysregulation. A developmental perspective, on the other hand, is essential in understanding the ontogeny of an individual.

Would the perennial debate between nature and nurture be put to rest with this integration? Hardly. Perhaps there is an adaptive value to human nature that causes this debate, i.e., the psychological traits to develop a bias toward the influences of innate givens versus environmental influences may have evolutionary advantages, just as body types do. Then, perhaps, tolerance of differing views may also be a trait that has evolved with homo sapiens. Evolution has been largely a passive process of genes adapting to changing environments. Recently, homo sapiens has changed the environment on a large scale. Now we have the means of actively determining both the environment and genes. For the first time in evolutionary history, homo sapiens finds itself to be master of its own evolution. Would the successors to homo sapiens be homo? sapiens? homo and sapiens? para sapiens maximus? With the cracking of the genetic code, Schroedinger’s cat of human evolution may soon be out of the bag.