LOQ LearningObjectiveQuestion

Why do researchers find human development interesting? Like most of the rest of us, they want 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 absorbed our father’s sperm helped form us as individuals. Genes predispose both our shared humanity and our individual differences.

But it also is true that our experiences form 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 (Farruggia et al., 2004; 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” (Rowe et al., 1994). 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, the differences between groups are small. We share a human nature.

Do adults differ from infants as a giant redwood differs from its seedling—differences mostly created by constant, gradual growth? Or do we change in some ways as a caterpillar differs from a butterfly—in distinct stages?

Researchers who focus on experience and learning typically view development as a slow, ongoing process. Those who emphasize the influence of our biology tend to see development as a process of maturation, as we pass through a series of stages or steps, guided by instructions programmed into our genes. Progress through the various stages may be quick or slow, but we all pass through the stages in the same order.

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 phases (summarized in FIGURE 3.1). But we will also see that some research casts doubt on the idea that life passes through neatly defined age-linked stages.

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 help us focus our attention on the forces and interests that affect us at different points in the life span. This close attention can help us understand how people of one age think and act differently when they arrive at a later age.

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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 once befriended later seem like total strangers? (At least one man I [DM] know would choose the second option. He failed to recognize a former classmate at his 40-year college reunion. That upset classmate was his long-ago first wife!)

Developmental psychologists’ research shows that we experience both stability and change. People predict that they will not change much in the future (Quoidbach et al., 2013). In some ways, they are correct. Some of our characteristics, such as temperament (emotional excitability), are very stable. When a research team studied 1000 people from age 3 to 32, they were struck by the consistency of temperament and emotionality across time (Slutske et al., 2012). Out-of-control 3-year-olds were the most likely, at age 32, to be out-of-control gamblers. Other research showed that the widest smilers in childhood and college photos were, years later, the adults most likely to enjoy enduring marriages (Hertenstein et al., 2009). And conscientious 12-year-olds tend to be, 40 years later, more occupationally successful (Spengler et al., 2015).

We cannot, however, predict all of our eventual traits based on our early years (Kagan, 1998; Kagan et al., 1978). Some traits, such as social attitudes, are much less stable than temperament, especially during the impressionable late adolescent years (Krosnick & Alwin, 1989; Rekker et al., 2015). And older children and adolescents can learn new ways of coping. It is true that delinquent children later have higher rates of work problems, substance abuse, and crime, but many confused and troubled children blossom into mature, successful adults (Moffitt et al., 2002; Roberts et al., 2001; Thomas & Chess, 1986). Happily for them, life is a process of becoming.

In some ways, we all change with age. Most shy, fearful toddlers begin opening up by age 4. In the years after adolescence, most people become more conscientious, self-disciplined, agreeable, and self-confident (Lucas & Donnellan, 2011; Roberts et al., 2003, 2006; Shaw et al., 2010). Conscientiousness increases especially during the twenties, and agreeableness during the thirties (Srivastava et al., 2003). Many a 20-year-old goof-off has matured into a 40-year-old business or cultural leader. (If you are the former, you aren’t done yet.) 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 hard-driving senior citizen.

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Life requires both stability and change. Stability increasingly marks our personality as we age (Briley & Tucker-Drob, 2014). (“As at 7, so at 70,” says a Jewish proverb.) And stability gives us our identity. It lets us depend on others and be concerned about the healthy development of the children in our lives. Our trust in our ability to change gives us hope for a brighter future and lets us adapt and grow with experience.