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 by the physical and social contexts in which they live, but they also play a role in influencing their development by interacting with and changing those contexts (Elder et al., 2016). Even infants influence the world around them and construct their own development through their interactions. Consider an infant who smiles at each adult he sees; he influences his world because adults are likely to smile, use “baby talk,” and play with him in response. The infant brings adults into close contact, making one-on-one interactions and creating opportunities for learning. By engaging the world around them, thinking, being curious, and interacting with people, objects, and the world around them, individuals of all ages are “manufacturers of their own development” (Flavell, 1992, p. 998).
It’s easy to see how this baby can influence the world around her and construct her own development through her interactions. By smiling at each adult she sees, she influences her world because adults are likely to smile, use “baby talk,” and play with her in response.
iStock/MartenBG
Nature and Nurture Influence Development
Perhaps the most fundamental question about lifespan human development concerns why people change in predictable ways over the course of their lifetimes. The answer reflects perhaps the oldest and most heated debate within the field of human development: the nature–nurture issue. Is development caused by nature or nurture? Explanations that rely on nature point to inborn genetic traits (heredity), maturational processes, and evolution as causes of developmental change. For example, most infants take their first steps at roughly the same age, suggesting a maturational trend that supports the role of nature in development (Payne & Isaacs, 2016). An alternative explanation for developmental change is nurture, the view that individuals are molded by the physical and social environment in which they are raised, including the home, school, workplace, neighborhood, and society. From this perspective, although most begin to walk at about the same time, environmental conditions can speed up or slow down the process. Infants who experience malnutrition may walk later than well-nourished infants, and