KEY THEME

Developmental psychology is the study of how people change over the lifespan.

KEY QUESTIONS

One way to look at the overall development of your life is to think of your life as a story. You, of course, are the main character. Your life story so far has had a distinct plot, occasional subplots, and a cast of supporting characters, including family, friends, and lovers.

Like every other person’s life story, yours has been influenced by factors beyond your control. One such factor is the unique combination of genes you inherited from your biological mother and father. Another is the historical era during which you grew up. James’s life story, for example, will be shaped by the fact that he is living in an era in which more people are learning about and accepting transgender people. Your individual development has also been shaped by the cultural, social, and family contexts within which you were raised.

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The patterns of your life story, and the life stories of countless other people, are the focus of developmental psychology—the study of how people change physically, cognitively, and socially throughout the lifespan. Developmental psychologists investigate the influence of biological, environmental, social, cultural, and behavioral factors on development at every age and stage of life.

The impact of these factors on individual development is greatly influenced by attitudes, perceptions, and personality characteristics. For example, the adjustment to middle school may be a breeze for one child but a nightmare for another. Gender identity, too, can affect individual development, as we saw in James’s story. So, although we are influenced by the events we experience, we also shape the meaning and consequences of those events.

Along with studying common patterns of growth and change, developmental psychologists look at the ways in which people differ in their development and life stories. As we’ll note several times in this chapter, the typical, or “normal,” pattern of development can also vary across cultures (Kagan, 2011; Molitor & Hsu, 2011).

Developmental psychologists use varied research methods, but two research strategies are particularly important in understanding how people develop: longitudinal and cross-sectional designs (Karmiloff-Smith & others, 2014). Research that utilizes a longitudinal design tracks a particular variable or group of variables in the same group of participants over time, sometimes for years. For example, a longitudinal study of the effects of day care might compare the social development of a matched group of participants, half of whom attended day care and half of whom didn’t, from infancy through high school graduation.

In contrast, research using a cross-sectional design studies a variable or group of variables among a group of participants at different ages or developmental stages. For example, to study the effect of aging on cognitive processes, developmental psychologists might compare memory abilities in 45-year-old, 55-year-old, and 65-year-old participants, looking for age-related differences.

Developmental psychologists often conceptualize the lifespan in terms of basic stages of development (see Table 9.1). Traditionally, the stages of the lifespan are defined by age, which implies that we experience relatively sudden, age-related changes as we move from one stage to the next. Indeed, some of life’s transitions are rather abrupt, such as entering the workforce, becoming a parent, or retiring. And some aspects of development, such as prenatal development and language development, are closely tied to critical periods, which are periods during which a child is maximally sensitive to environmental influences.

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Still, most of our physical, cognitive, and social changes occur gradually. As we trace the typical course of human development in this chapter, the theme of gradually unfolding changes throughout the ages and stages of life will become more evident. Another important theme in developmental psychology is the interaction between heredity and environment. Traditionally, this was called the nature—nurture issue. Although we are born with a specific genetic potential that we inherit from our biological parents, our environment influences how, when, and whether that potential is expressed. In turn, our genetic inheritance influences the ways in which we experience and interact with the environment (Diamond, 2009; Meaney, 2010).