and are not easily studied, as they are not experienced by most peopl—and the nature of nonnormative events varies widely. With age, nonnormative influences become more powerful determinants of development.
Developmental Science Is Multidisciplinary
Psychologists, sociologists, anthropologists, biologists, neuroscientists, and medical researchers all conduct research that is relevant to understanding aspects of human development. For example, consider cognitive development. Children’s performance on cognitive measures, such as problem solving, are influenced by their physical health and nutrition (Anjos et al., 2013), interactions with peers (Holmes, Kim-Spoon, & Deater-Deckard, 2016), and neurological development (Ullman, Almeida, & Klingberg, 2014)—findings from the fields of medicine, psychology, and neuroscience, respectively. To understand how people develop at all periods in life, developmental scientists must combine insights from all of these disciplines.
Thinking in Context 1.1
1 Describe your own development. In what ways have you changed over your lifetime? What characteristics have remained the same?
2 Consider your own experience and provide examples from your life that illustrate the multidimensional nature of your own development. Can you do the same for multidirectionality and for plasticity? How has the context in which you were raised and live influenced your development?
3 Compare the historical context in which you, your parents, and your grandparents were raised. How did historical and societal influences affect your grandparents’ development, their worldview, and their childrearing strategies? What about your parents? How might historical influences affect your own development, worldview, and perspective on parenting?
Basic Issues in Lifespan Human Development
Developmental scientists agree that people change throughout life and show increases in some capacities and decreases in others from conception to death. Yet they may sometimes disagree about how development proceeds, what specific changes occur, and what causes the changes. Developmental scientists’ explanations of how people grow and change over their lives are influenced by their perspectives on three basic issues, or fundamental questions, about human development:
1 Do people change gradually often imperceptibly, over time, or is developmental change sudden and dramatic?
2 What role do people play in their own development—how much are they influenced by their surroundings, and how much do they influence their surroundings?
3 To what extent is development a function of inborn genetic characteristics, and to what extent is it affected by the environment in which individuals live?
The following sections examine each of these questions.
Continuities and Discontinuities in Development
Do children slowly grow into adults, steadily gaining more knowledge and experience and becoming better at reasoning? Or do they grow in spurts, showing sudden, large gains in knowledge and reasoning capacities? In other words, is developmental change continuous, characterized by slow and gradual change, or discontinuous, characterized by abrupt change? As shown in Figure 1.2, a discontinuous view of development emphasizes sudden transformation, whereas a continuous view emphasizes gradual and steady changes.
Scientists who argue that development is continuous point to slow and cumulative changes, such as a child slowly gaining experience, expanding his or her vocabulary, and learning strategies to become quicker at problem solving (Siegler, 2016). Similarly, they point out that middle-aged adults experience gradual losses of muscle and strength (Keller & Engelhardt, 2013).
The discontinuous view of development describes the changes we experience as large and abrupt, with individuals of various ages dramatically different from one another. For example, puberty transforms children’s bodies into more adult-like adolescent bodies (Wolf & Long, 2016), infants’ understanding and capacity for language is fundamentally different from that of school-aged children (Hoff, 2014), and children make leaps in their reasoning abilities over the course of childhood, such as from believing that robotic dogs and other inanimate objects are alive to understanding that life is a biological process (Beran, Ramirez-Serrano, Kuzyk, Fior, & Nugent, 2011; Zaitchik, Iqbal, & Carey, 2014).
It was once believed that development was either continuous or discontinuous—but not both. Today, developmental scientists agree that development includes both continuity and discontinuity (Lerner, Agans, DeSouza, & Hershberg, 2014). Whether a particular developmental change appears continuous or discontinuous depends in part on our point of view. For example, consider human growth. We often think of increases in height as involving a slow and steady process; each month, an infant is taller than the prior month, illustrating continuous change. However, as shown in Figure 1.3, when researchers measured infants’ height every day, they discovered that infants have growth days and nongrowth days, days in which they show rapid change in height interspersed with days in which there is no change in height, illustrating discontinuous change (Lampl, Johnson, Frongillo, & Frongillo, 2001). In this example, monthly measurements of infant height suggest gradual increases, but daily measurements show spurts of growth, each lasting 24 hours or less. Thus, whether a given phenomenon, such as height, is described as continuous or discontinuous can vary. Most developmental scientists agree that some aspects of lifespan development are best described as continuous and others as discontinuous (Miller, 2016).
Individuals Are Active in Development
Do people have a role in influencing how they change over their lifetimes? That is, are people active in influencing their own development? Taking an active role means that they interact with and influence the world around them, create experiences that lead to developmental change, and thereby influence how they themselves change over the lifespan. Alternatively, if individuals take a passive role in their development, they are shaped by, but do not influence, the world around them.
Figure 1.2 Continuous and Discontinuous Development
Source: Adapted from End of the Game (2014) Child Development 101, History and Theory, https://endofthegame.net/2014/04/15/child-development-101-history-and-theory/3/
Figure 1.3 Infant Growth: A Continuous or Discontinuous Process?
Infants’ growth occurs in a random series of roughly 1-centimeter spurts in height that occur over 24 hours or less. The overall pattern of growth entails increases in height, but whether the growth appears to be continuous or discontinuous depends on our point of view.
Source: Figure 1 from Lampl, M., Veldhuis, J. D., & Johnson, M. L. (1992.) Saltation and stasis: A model of human growth. Science, 258, 801-803. With permission from AAAS.
The prevailing view among developmental scientists is that people are active contributors to their own development (Lerner et al., 2014). People are influenced
