1. Weaver et al propose that among rats, maternal behavior towards newborn pups influences their cortisol response to stress via epigenetic mechanisms that change the expression of glucocorticoid receptor gene for the rest of the pup’s life. They argue that because epigenetic patterns are established at specific developmental periods, there is extreme time sensitivity to when the pup is exposed to particular maternal behaviors (licking and grooming, in this case), and maternal behavior before or after that sensitive period window is not as important. Do you think this mechanism is relevant in humans? If so, what behaviors are most analogous to “maternal licking and grooming”?
As with any study of non-human species, it is impossible to know for sure if the same biological mechanisms apply to humans. However, given the high degree of biological similarities between rats and humans and analogous studies in humans, it seems that this mechanism is also relevant in humans. One study in humans that may have epigenetic consequences is the strange situation study by Mary Ainsworth that was used to develop attachment theory. Her study demonstrated that children can be categorized into four different attachment styles based on their reaction to various situations involving their caregiver and a stranger. Further studies have concluded that there is a relationship among parenting styles, attachment styles, and psychophysiological mechanisms such as increased cortisol levels, particularly in anxious-ambivalent types. This type of attachment corresponds to unpredictably responsive caregiving. As such, one might conclude that epigenetic patterns are a function of the frequency of caregiving rather than the specific activity. However, one can also infer that analogous behaviors in human parenting to maternal licking and grooming in rats would include hugging, cuddling, kissing, feeding, talking, and being present.
2. Gruenewald, in contrast, emphasize the cumulative effects of SES adversity on a multi-system allostatic load measure. Do you think that the Gruenewald findings are consistent, inconsistent, or unrelated to the Weaver findings? Explain.
Assuming that Weaver’s findings can be applied to humans, his/her proposal that maternal behavior towards offspring influences cortisol levels does not seem to contradict Gruenewald’s findings that SES (measured in terms of parent educational attainment, welfare status, financial situation, adult educational attainment, household income, difficulty paying bills, availability of money to meet basic needs, and current financial situation) contributes to allostatic load. Both studies point to environmental influences on individual outcomes, so they are consistent in this sense. But there are a number of possibilities in how maternal behavior and Gruenewald’s SES measures interact and potentially contribute to the same outcome. One possibility is that maternal behaviors also contribute to allostatic load. Alternatively, measures of SES such as parent educational attainment, welfare status, financial situation, etc. influence maternal behaviors, which in turn affect epigenetic receptors. Further study of these relationships would be needed to determine if Gruenewald and Weaver’s findings are unrelated or consistent and if so, how they are related in a potentially complex way.
3. Hertzmann and Boyce argue that “it is not genes or environment, nor is it genes and environment, but rather it is gene-by-environment interactions that influence developmental trajectories.” To what extent do you think that GxE interactions can contribute to major disparities along racial/ethnic, socioeconomic, or geographic dimensions?
Without further evidence that demonstrates how gene-by-environment interactions contribute to disparities, it is impossible to accurately quantify the “extent” to which this occurs. Based on personal and anecdotal experiences, this theory is intuitively appealing. It also seems consistent with some theories of anxiety, which could be considered a marker of “biological sensitivity,” that environments of very high and very low childhood adversity result in stress-reactive profiles. However, the extent to which disparities are caused by GxE interactions could be mitigated by consciousness or “free will.” For example, there may be examples of individuals who do not fit this perfect U shape relationship between adversity and biological sensitivity that the authors describe. As such, this seems to be a fundamental philosophical question of free will versus determinism. A deterministic perspective would conclude that an individual’s fate is solely the function of variables beyond one’s control such as genes and environment. However, it appears that there isn’t a perfect predictive measure of life outcomes yet, which does not preclude the possibility that there is one, so the evidence currently seems to suggest that there is (are) some other factor(s), perhaps free will, that also influence life outcomes.