10-1 What three issues have engaged developmental psychologists?

Researchers find human development interesting for the same reasons most of the rest of us do—they are eager to understand more about how we’ve become our current selves, and how we may change in the years ahead. Developmental psychology examines our physical, cognitive, and social development across the life span, with a focus on three major issues:

The unique gene combination created when our mother’s egg engulfed our father’s sperm helped form us, as individuals. Genes predispose both our shared humanity and our individual differences.

But our experiences also shape us. Our families and peer relationships teach us how to think and act. Even differences initiated by our nature may be amplified by our nurture. We are not formed by either nature or nurture, but by the interaction between them. Biological, psychological, and social-cultural forces interact.

Mindful of how others differ from us, however, we often fail to notice the similarities stemming from our shared biology. Regardless of our culture, we humans share the same life cycle. We speak to our infants in similar ways and respond similarly to their coos and cries (Bornstein et al., 1992a,b). All over the world, the children of warm and supportive parents feel better about themselves and are less hostile than are the children of punishing and rejecting parents (Rohner, 1986; Scott et al., 1991). Although ethnic groups have differed in some ways, including average school achievement, the differences are “no more than skin deep.” To the extent that family structure, peer influences, and parental education predict behavior in one of these ethnic groups, they do so for the others as well. Compared with the person-to-person differences within groups, between-group differences are small.

Do adults differ from infants as a giant redwood differs from its seedling—a difference created by gradual, cumulative growth? Or do they differ as a butterfly differs from a caterpillar—a difference of distinct stages?

Researchers who emphasize experience and learning typically see development as a slow, continuous shaping process. Those who emphasize biological maturation tend to see development as a sequence of genetically predisposed stages or steps: Although progress through the various stages may be quick or slow, everyone passes through the stages in the same order.

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Are there clear-cut stages of psychological development, as there are physical stages such as walking before running? The stage theories we will consider—of Jean Piaget on cognitive development, Lawrence Kohlberg on moral development, and Erik Erikson on psychosocial development—propose developmental stages (summarized in FIGURE 10.1). But as we will also see, some research casts doubt on the idea that life proceeds through neatly defined age-linked stages. Young children have some abilities Piaget attributed to later stages. Kohlberg’s work reflected an individualist worldview and emphasized thinking over acting. And adult life does not progress through a fixed, predictable series of steps. Chance events can influence us in ways we would never have predicted.

Although many modern developmental psychologists do not identify as stage theorists, the stage concept remains useful. The human brain does experience growth spurts during childhood and puberty that correspond roughly to Piaget’s stages (Thatcher et al., 1987). And stage theories contribute a developmental perspective on the whole life span, by suggesting how people of one age think and act differently when they arrive at a later age.

As we follow lives through time, do we find more evidence for stability or change? If reunited with a long-lost grade-school friend, do we instantly realize that “it’s the same old Andy”? Or do people we befriend during one period of life seem like strangers at a later period? (At least one acquaintance of mine [DM’s] would choose the second option. He failed to recognize a former classmate at his 40-year college reunion. The aghast classmate was his long-ago first wife.)

Research reveals that we experience both stability and change. Some of our characteristics, such as temperament, are very stable:

“As at 7, so at 70,” says a Jewish proverb. People predict that they will not change much in the future (Quoidbach et al., 2013). In some ways they are correct. The widest smilers in childhood and college photos are, years later, the ones most likely to enjoy enduring marriages (Hertenstein et al., 2009).

We cannot, however, predict all aspects of our future selves based on our early life. Our social attitudes, for example, are much less stable than our temperament (Moss & Susman, 1980). Older children and adolescents learn new ways of coping. Although delinquent children have elevated rates of later problems, many confused and troubled children blossom into mature, successful adults (Moffitt et al., 2002; Roberts et al., 2013; Thomas & Chess, 1986). The struggles of the present may be laying a foundation for a happier tomorrow. Life is a process of becoming.

In some ways, we all change with age. Most shy, fearful toddlers begin opening up by age 4, and most people become more conscientious, stable, agreeable, and self-confident in the years after adolescence (Lucas & Donnellan, 2009; Roberts & Mroczek, 2008; Shaw et al., 2010). Many irresponsible 18-year-olds have matured into 40-year-old business or cultural leaders. (If you are the former, you aren’t done yet.) Openness, self-esteem, and agreeableness often peak in midlife (Lucas & Donnellan, 2011; Orth et al., 2012, 2015; Specht et al., 2011). Such changes can occur without changing a person’s position relative to others of the same age. The hard-driving young adult may mellow by later life, yet still be a relatively driven senior citizen.

Life requires both stability and change. Stability provides our identity. It enables us to depend on others and be concerned about children’s healthy development. Our potential for change gives us our hope for a brighter future. It motivates our concerns about present influences and lets us adapt and grow with experience.