Child Development From Infancy to Adolescence. Laura E. Levine
effects of early life experiences on the epigenome and on later behavior also depend on the particular versions of genes, called alleles, inherited by the individual. For example, researchers have examined the role of both genes and environment in the development of children’s externalizing behavior, such as aggression and oppositional behavior (Windhorst et al., 2016). They focused on genes related to the production of dopamine, a chemical in the brain that is involved with motivation and the regulation of attention, emotion, and activity. Using genome-wide association, they found that children with different alleles for genes associated with dopamine responded differently to the experience of harsh parenting in early childhood. For children who had warm parenting, those who had one type of allele showed more externalizing behavior and those with a different type of allele showed less. However, for children who experienced harsh parenting, the type of allele they had did not relate to the degree of externalizing behavior. It appears that harsh parenting overrules the role of gene variance in the development of aggressive and oppositional behavior. These types of gene-by-environment interactions have also been found for different genes relating to depression, posttraumatic stress disorder, and negative emotionality in infants (Binder et al., 2008; Caspi et al., 2003; Green et al., 2016).
Allele: Different forms of one gene.
Complexities in the Study of Gene-Environment Interaction
Another example of recent research designed to show the interaction of genes and environment has focused on the timing of the onset of puberty, especially for girls. Puberty is triggered by the action of certain genes, and its timing for an individual is in part inherited. If your mother or father entered puberty at an early age, you are also more likely to experience puberty early (Wohlfahrt-Veje et al., 2016). However, a variety of environmental factors also appear to turn on the genes for puberty.
As we described in the section on evolutionary theory in Chapter 2, there is evidence that girls are more likely to enter puberty earlier when they experience adverse experiences such as child abuse or father absence early in life (Belsky, Ruttle, Boyce, Armstrong, & Essex, 2015). This finding appears to indicate an environmental effect on the timing of puberty, although a purely genetic explanation may be adequate. One particular gene associated with aggression in men (the X-linked AR gene) also can be inherited by a daughter. However, the principle of pleiotropism says that a gene may have more than one outcome. In girls, this gene is not associated with aggression but instead acts to trigger early puberty. Therefore, a father with this gene is more likely to be aggressive and have more interpersonal conflict, creating a more difficult family life in the process. If his daughter inherits this gene, instead of influencing her to be more aggressive, it triggers early puberty. It is not the father’s aggression that turned on the gene for puberty, but rather the gene itself that both promotes aggression in the father and turns on early puberty in the daughter (Posner, 2006). This is another example of the complexity that awaits us as we try to fully understand the interaction of genes and the environment.
How Genes Shape the Environment
So far, we have described the way genes affect physical and biological processes and the way the environment influences the expression of genes to produce various developmental outcomes. In a third developmental mechanism, genes influence the nature of the environment in which they exist.
Sandra Scarr (1992) proposed that one way to think about how genes shape the environment is to see them as passive, active, or evocative. With a passive gene-environment interaction, the genes don’t have to do much to be expressed, as when children are born into a family that provides them with both their genes and an environment that encourages the expression of those genes. For example, singer Bruno Mars probably inherited genes associated with musicality from his father who was a Latin percussionist and his mother who was a singer. However, his training in music that began at age 4 when he did an Elvis impersonation as part of his family’s Las Vegas-style review show also provided an environment that supported his talent as he grew up. He has gone on to a highly successful career in music.
Passive gene-environment interaction: When a child’s family shares his own genetically determined abilities and interests.
Following in the family footsteps. Bruno Mars began performing as “Little Elvis” in his family’s musical act at the age of 4. As an adult, he has gone on to sell over 11 million albums worldwide and was named entertainer of the year at the 2017 American Music Awards. He likely received both genes and environmental influences that set him on his path to a successful singing career.
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An active gene-environment interaction occurs when genes become a driving force for children to seek out experiences that fit their genetic endowments (Jaffee & Price, 2008). A child with genes that promote risk-taking may be drawn like a magnet to snowboarding, bungee jumping, or whatever is offered that provides a physical and risky challenge. On the other hand, a child with a genetic predisposition to be timid will seek out activities that are solitary and not overly stimulating or exciting. As we described in Chapter 1, this type of gene effect is also called niche-picking or niche-building. You find the part of your environment (the niche) in which you feel most comfortable, and you actively make this choice (Feinberg, Reiss, Neiderhiser, & Hetherington, 2005).
Active gene-environment interaction: When children’s genetic endowment becomes a driving force to seek out experiences that fit their genetic endowments.
Finally, with evocative gene-environment interaction, genes cause children to act in a way that draws out or “evokes” certain responses from those around them. For example, individuals with certain forms of a gene related to the production of the hormone oxytocin were more outgoing and less shy compared to individuals with a different form of the same gene. Researchers found that the more friendly behavior exhibited by these individuals evoked a positive response from people in their social world, resulting in a higher level of social support and more friends (Creswell et al., 2015).
Evocative gene-environment interaction: When children’s genetic endowment causes them to act in a way that draws out or “evokes” certain responses from those around them.
It is important to realize that all genes may operate in all three of these ways. A child who has inherited genes for musicality and has a musical family may also actively seek out musical experiences outside of the family and this behavior evokes certain responses from people such as music teachers who further promote the child’s musical interests and abilities. Our genes play out their influence in our environment, but they also have an important role in creating our environment.
Check Your Understanding
Knowledge Questions
1 What does the concept of canalization describe?
2 What is epigenetics?
3 What are the differences between passive gene-environment interaction, active gene-environment interaction, and evocative gene-environment interaction?
Critical Thinking
Joanna has inherited genes that have been connected with mathematical skill. Describe how her genetic inheritance might