Adaptable Ancestors

The high level of plasticity shown by children today was also a feature of our forechildren. Experiences early in life can modify the morphology or behavior of an animal and result in new pressures that can be the focus of natural selection. Behavior, in fact, takes the lead in evolution, because it is more susceptible to change than morphology or genes. Most of the changes early in development, at least for mammals, were accomplished in the presence of mothers. To a significant extent, mothers are the environment for young mammals, making mothers the environment for evolutionary change. Significant behavioral changes in evolution are most likely to occur in large-brained animals, who are better able to deal with novel environments through innovation and social transmission of information than smaller-brained animals.

Epilogue

The final chapter summarizes the major themes of this book, loosely following the content of Chapters 1 through 7. The first section highlights the principles and assumptions of evolutionary developmental psychology, emphasizing that adaptations occurred at all life stages, not just in adults. The second section emphasizes the role of plasticity in both development and evolution, noting that plasticity is greatest early in life. This is followed by a section focusing on the role of timing in evolution, especially genetic-based differences in developmental timing, or heterochrony, with neoteny being especially important for human evolution. The fourth section examines the claim that humans are a neotenous species, as seen in aspects of its physical, behavioral, and cognitive development/evolution. The fifth section examines human hypersociality as being due to modification of great ape ontogeny into unique human social-cognitive abilities, followed by a look at evolutionary mismatches particular to specific stages of life.

Evolutionary Mismatches in the Development of Today’s Children

Differences between modern and ancient environments sometimes cause evolutionary mismatches. Many children are following an exceptionally slow life history strategy and as a result are safer and engage in less risky behavior than in the past (safetyism), although many are more psychologically fragile and less resilient. Excessive use of social media is associated with poorer physical and mental health, including increases in depression, anxiety, and loneliness. Today’s adolescents display hyper-individualism that emphasizes personal freedom and achievement. The relative lack of social bonding in individualistic societies is associated with increases in loneliness and mental health problems and can sometimes be exaggerated by social media use. Modern schools represent a mismatch with the environments of our forechildren. Similarly, young children’s exposure to digital media may have detrimental effects on subsequent learning and psychological development. Parents and educators can identify problems associated with evolutionary mismatches and design environments that make the lives of children happier.

Embryos and Ancestors

Evolutionary developmental biology, or Evo Devo, examines how developmental mechanisms affect evolutionary change. Heterochrony refers to genetic-based differences in developmental timing. One important type of heterochrony for humans is neoteny, which refers to the retention of juvenile traits into later development. Humans are a neotenous species, as seen in infants’ features of “babyness,” which promote attention and caring from adults, extending the primate prenatal brain growth rate well past birth, and a reduction of reactive aggression relative to great apes, which facilitated increased cooperation among group members. Homo sapiens extended the time it takes to reach adulthood by inventing new two life stages—childhood and adolescence. The social and cognitive abilities of Homo sapiens’ youth may be well suited to the childhood and adolescent stages and to the attainment of skills necessary for developing into functional adults.

Developing the Evolved Social Brain

For human hypersociality to evolve required that natural selection operate both at the levels of the individual and the group as described by multilevel selection theory. According to the social brain hypothesis, increased social cognition was the driving force in human social-cognitive evolution. Infants evolved “psychological weapons” designed to obtain attention and caregiving from adults. According to Tomasello’s shared intentionality theory, infants view others as intentional agents, as reflected in shared attention beginning around 9 months, and later, between 3 and 5 years of age, in collective intentionality, in which children establish a group-minded “we” with other people. The development and evolution of hypersociality is reflected in: treating others as intentional agents, perspective taking, empathy, normativity, social learning, prosociality (helping, sharing, sense of fairness), and collaboration. Each of these and other social-cognitive abilities were necessary for the evolution of a hypersocial species and evolved as a result of changes in great ape ontogeny.

The Adaptive Value of Immaturity (or The Benefits of Being Young at Heart)

There are many aspects of young children’s thinking that are immature on the surface but have adaptive value for the young learner, a form of cognitive neoteny. These include young children’s self-centered, or egocentric, perspective; inefficient aspects of memory; tendencies to copy all relevant and irrelevant actions of adult models (overimitation); tendencies to overestimate their abilities; and strong propensity to play. Also included are special abilities to learn, and even create, language, due, in part, to aspects of immature cognition. Ancient human adults retained many youthful characteristics including behavioral plasticity, curiosity, play, imagination, and optimism. These characteristics, coupled with enhanced reasoning and executive function, have led to advances in material and intellectual culture far surpassing anything achieved by other species and to the evolution of the modern human mind.

Changeable Children

Plasticity is an evolved feature of Homo sapiens and is greatest early in development. Plasticity permits children to adjust to diverse environments and still grow up to be productive members of their society. This can be seen from the variety of rearing environments found in cultures around the world, from the child-adoring hunter-gatherers to those that view children as drains on resources. Plasticity is not infinite, however, but declines with age. Natural selection has provided children with sensitivity to early environments and the plasticity to entrain their development in adaptive ways, as explained by life history theory. Recent advances have provided important evidence for the proximal causes of changes in behavior as a result of experience—epigenetics, how genes are expressed in different contexts. We can now begin to understand plasticity at the level of the gene, and this has implications for understanding all forms of human functioning.

Children, Childhood, and Development in Evolutionary Perspective

This chapter highlights the principles of evolutionary psychology and evolutionary developmental psychology, emphasizing that adaptations occurred at all life stages, not just in adults, and may have been especially important early in life. Infants, children, and adolescents evolved sets of behaviors, emotions, and cognitions adapted to their immediate environments and not necessarily to future ones. These adaptations are inherited but only develop properly through interaction with a supportive context. Humans evolved most of their unique psychological features over the last 2 million years or so, living as hunter-gatherers on the savannahs of Africa, and these are the environments in which human nature evolved. Many scholars contend that hunter-gatherer childhoods are the models upon which we should judge the practices we use in raising children today.