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”?
Although there is much evidence about developmentally important periods for humans when core functions are most efficiently acquired such as language learning up to age 7 or facility for certain types of learning during certain periods, the impact of these “critical periods” on response to stress is less clear. One must always be cautious in applying lessons from animal studies uncritically to humans. I suspect the mechanism may be more complicated in humans. Rather than all or nothing, the impact of experience on processing of stress likely impacts humans across the life course as suggested in the Grunewald reading. More recent stressful experiences may in someways have bigger impacts on humans who have the ability to manipulate language and memories in a way that animals do not. A possible analogous mechanism may be simply maternal or parental time spent with children, which may be more significantly limited for low SES parents who due to less material resources may need to spend less time with young children.
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.
The Grunewald findings suggested that the effect of adversity is cumulative over the life course, or at least has an impact at any time, with a trend towards greater impact from more recent adversity. I suspect these findings may be unrelated. For one, the Grunewald findings are not longitudinal and are subject to significant recall bias, perhaps overemphasizing the impact of recent rather than remote stress. The impact of adversity on biological systems may also be more complex than either model. There may be important early developmental periods that condition certain stress responses. Early life adversity may impact unconscious responses to stress. SES adversity over the life course could either condition these responses or impact different biopsychological systems such as mood, resilience, etc.
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?
Hertzmann and Boyce argue that rather than a synergistic effect of environment and genes on developmental trajectories, they may function more like a multiplicative interaction. Certain genetic makeups could predispose to depression, burnout, etc. that are only activated in specific environments of adversity. I do think a GxE interaction could explain the complexity of the impact of racism, SES, and geographic adversity on health. Interaction could explain why certain individuals have greater health impacts of adverse circumstances while others are less affected. Specific types of adversity could be linked to diverse phenotypes in the context of different genetic make-ups. It is likely that these interactions are complex and are unlikely to be explained by single gene-environment dyads. Of course, GxE interactions are likely not the only explanation and we should not minimize the importance of structural factors. If there are limited employment opportunities for everyone in a neighborhood, it may not matter what GxE interaction is occurring as few people have a chance to be successful. An important example is the school to prison pipeline that results in an incarceration history for a large number of African-American men, effectively limiting the employment potential for entire groups irrespective of genetic makeup. These interactions are more likely to have an impact on the margins where there are some, albeit somewhat scarce opportunities for success.