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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.