is known as epigenetics (Moore, 2017). The term epigenetics literally means “above the gene.” Individuals are influenced by both genetic and contextual factors; however, as shown in Figure 1.5, some contextual factors can determine whether and how genetic capacities are expressed or shown.
Figure 1.5 Interaction of Genetic and Environmental Factors
Development is influenced by the dynamic interplay of genetic and environmental factors. Genetic predispositions may influence how we experience environmental factors, and environmental factors may influence how genes are expressed.
Source:, Picker (2005).
As an example, contextual factors such as gravity, light, temperature, and moisture influence how genes are expressed and therefore how individuals develop (Meaney, 2017). For instance, in some reptiles such as crocodiles, sex is determined by the temperature in which the organism develops. Eggs incubated at one range of temperatures produce male crocodiles and at another temperature produce female crocodiles (Pezaro, Doody, & Thompson, 2017).
According to evolutionary developmental theory, genetic factors and biological predispositions interact with the physical and social environment to influence development, and Darwinian natural selection determines what genes and traits are passed on to the next generation (Bjorklund, 2018a; Witherington & Lickliter, 2016). Children are viewed as active in their development, influencing their contexts, responding to the demands for adaptation posed by their contexts, and constantly interacting with and adapting to the world around them. The relevance of both biological and contextual factors to human development is indisputable, and most developmental scientists appreciate the contributions of evolutionary developmental theory (DelGiudice, 2018; Frankenhuis & Tiokhin, 2018; Legare, Clegg, & Wen, 2018). The ways in which biology and context interact and their influence on development change over the course of the lifetime, as we will discuss throughout this book.
Dynamic Systems Theory
Some of the major concepts that we have discussed throughout this chapter include the interaction of genetics and environment and the active role of children in their own development. Children are motivated to understand their experience and control their environment. Each child’s characteristics and environmental circumstances and interactions are unique and influence how the child approaches developmental tasks and problems, resulting in unique patterns of functioning. Esther Thelen’s dynamic systems theory posits that children’s developmental domains, maturation, and environment form an integrated system that is constantly changing, resulting in developmental change and the emergence of new abilities (Thelen, 1995, 2000).
Many childhood milestones, such as an infant’s first steps or first word, might look like isolated achievements, but they actually develop systematically and are the result of skill-building, with each new skill (such as pulling up to stand or babbling sounds) preparing an infant to tackle the next (Thelen, 1995, 2000). Simple actions and abilities are combined to provide more complex and effective ways for babies to explore and engage the world. An infant might combine the distinct abilities to sit upright, hold the head upright, match motor movements to vision, reach out an arm, and grasp to coordinate reaching movements to obtain a desired object (Corbetta & Snapp-Childs, 2009; Spencer, Vereijken, Diedrich, & Thelen, 2000). Development reflects goal-oriented behavior because it is initiated by the infant or child’s desire to accomplish something, such as picking up a toy or expressing him- or herself. Infants’ abilities and their immediate environments, including environmental supports and constraints, determine whether and how the goal can be achieved (Spencer et al., 2000). Although Esther Thelen described developmental systems theory with motor development in mind, theorists are applying it to understand children’s cognitive and emotional development as well as mental health (Guo, Garfin, Ly, & Goldberg, 2017; Mascolo, van Geert, Steenbeek, & Fischer, 2016).
The many theories of human development offer complementary and contrasting views of how we change throughout our lifetimes. Table 1.3 provides a comparison of theories of human development.
Table 1.3
Thinking in Context 1.3
Just after their healthy baby girl is born, Latisha and Devonne are overwhelmed by the intense love they feel for her. Like most new parents, they also worry about their new responsibility. They hope that their baby will develop a strong, secure, and close bond to them. They want their baby to feel loved and to love them.
1 What advice would a psychoanalytic theorist give Latisha and Devonne? Contrast psychoanalytic with behaviorist or social learning perspectives. How might a behaviorist theorist approach this question?
2 How might an evolutionary developmental theorist explain bonding between parents and infants? What advice might an evolutionary developmental theorist give to Latisha and Devonne?
3 Considering bioecological systems theory, what microsystem and mesosystem factors influence the parent–child bond? What role might exosystem and macrosystem factors take?
Research in Human Development
Developmental scientists conduct research to gather information and answer questions about how children grow and change. They devise theories to organize what they learn from research and to suggest new hypotheses to test in research studies. In turn, research findings are used to modify theories. By conducting multiple studies over time, developmental scientists refine their theories about child development and determine new questions to ask.
The Scientific Method
Researchers employ the scientific method, a process of posing and answering questions by making careful and systematic observations and gathering information. The scientific method provides an organized way of formulating questions, gathering and evaluating information, and determining and communicating answers. Its basic steps are as follows:
1 Identify the research question or problem to be studied and formulate the hypothesis, or proposed explanation, to be tested.
2 Gather information to address the research question.
3 Summarize the information gathered and determine whether the hypothesis is refuted, or shown to be false.
4 Interpret the summarized information, consider the findings in light of prior research studies, and share them with the scientific community and world at large.
In practice, the scientific method usually does not proceed in such a straightforward, linear fashion. Frequently, research studies raise as many questions as they answer—and sometimes more. Unexpected findings can prompt new studies. For example, researchers may repeat an experiment (called a replication) to see whether the results are the same as previous ones. Sometimes analyses reveal flaws in data collection methods or research design, prompting a revised study. Experts may also disagree on the interpretation of a study. Researchers may then conduct new studies to test new hypotheses and shed more light on a given topic. For all of these reasons, scientists often say the scientific method is “messy.”
Methods of Data Collection
The basic challenge that developmental scientists face in conducting research is determining how to measure their topic of interest. Scientists use the term data to refer to the information they collect. How can we gather data about children? Should we simply talk with them? Watch them as they play? Hook them up to machines that measure physiological activity such as heart rate or brain waves? Developmental scientists use a variety of different methods to collect information.