Читать книгу Lifespan Development - Tara L. Kuther - Страница 141

We have seen that development is influenced by the dynamic interaction of biological and contextual forces. Genes provide a blueprint for development, but phenotypic outcomes, individuals’ characteristics, are not predetermined. Our genes are expressed as different phenotypes in different contexts or situations, known as epigenetics (Moore, 2017). The term epigenetics literally means “above the gene.” The epigenome is a molecule that stretches along the length of DNA and provides instructions to genes, determining how they are expressed, whether they are turned on or off. Epigenetic mechanisms determine how genetic instructions are carried out to determine the phenotype (Lester, Conradt, & Marsit, 2016). At birth, each cell in our body turns on only a fraction of its genes. Genes continue to be turned on and off over the course of development and also in response to the environment (Meaney, 2017). Environmental factors such as toxins, injuries, crowding, diet, and responsive parenting can influence the expression of genetic traits. In this way, even traits that are highly canalized can be influenced by the environment.

For example, consider brain development. Providing an infant with a healthy diet and opportunities to explore the world will support the development of brain cells, governed by genes that are switched on or off. Brain development influences motor development, further supporting the infant’s exploration of the physical and social world, thereby promoting cognitive and social development. Active engagement with the world encourages connections among brain cells. Exposure to toxins or extreme trauma might suppress the activity of some genes, potentially influencing brain development and its cascading effects on motor, cognitive, and social development. In this way, an individual’s neurological capacities are the result of epigenetic interactions among genes and contextual factors that determine his or her phenotype (Lerner & Overton, 2017). These complex interactions are illustrated in Figure 2.11 (Dodge & Rutter, 2011). Interactions between heredity and environment change throughout development as does the role we play in constructing environments that support our genotypes, influence our epigenome, and determine who we become (Lickliter & Witherington, 2017). For a striking example of epigenetics, see the Applying Developmental Science feature.

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Figure 2.11 Epigenetic Framework

Source: Gottlieb (2007). With permission from John Wiley & Sons.