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”?
I had a slightly different take on the Weaver paper than the prompt suggests. It’s clear to me that Weaver et al conclude that the first week of postnatal life is a “critical period” for the effects of early experience but it is not clear to me that they are arguing that other periods of life are less significant and would not be sensitive to specific interventions later over the life course of the rats. Rather that in the subsequent natural life span they observed, the early epigenetic changes persisted. (Full disclosure, it’s possible I’m getting lost in the methods or that there other work may suggest this). Regardless, this mechanism is relevant in humans to the extent that it is likely true that interactive human behaviors lead to epigenetic changes and that there are certain periods during the life course that may be more sensitive to the presence or absence of these types of behaviors. It is hard to imagine, though, that there is a single critical period, given what we know of the dramatic developmental changes over a human life course, with one simple example being that brain plasticity extends fully into the third decade. Behaviors most similar to maternal licking and grooming in humans may include close physical interactions in the neonatal period (skin to skin contact, breastfeeding), but hormonal changes induced by physical contact even later in life such as hugging suggests a potential wide range of mediators in the human experience.
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.
Based on my take on the Weaver paper as above, I find the Gruenewald findings to be consistent with the work by Weaver et al. The latter suggests one important period contributing to multi-system allostatic load measures among the many potential points of significance suggested by Gruenewald. I would expect subsequent studies to identify additional critical periods contributing to a wide range of epigenetic changes associated with the allostatic load measure.
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?
I agree that gene-by-environment interactions can lead to major disparities across a variety of dimensions. The expressed phenotypes of similar genes will result in disparities as a result of racial/ethnic discrimination as well as socioeconomic/geographic determinants. But it is important to incorporate the results of the work by Weaver et al and Gruenewald into this concept, i.e. that environment can trigger significant epigenetic changes and so the effect is more bi-directional than it might at first seem.