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”?
Yes, this mechanism could easily apply in humans as well. Interestingly, many so-called “Baby-friendly” labor and delivery floors practice what some have termed “Kangaroo care,” in which after the baby is born, baby is placed skin-to-skin on mother’s chest, and it is a priority to keep them snuggled together for the first hour of life, not even to be transferred to father’s hold, to maximize mother-newborn bonding. This key hour after birth seems analogous to the way Weaver et al describe the first week of the newborn pups.
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 Gruenewald and Weaver readings are not mutually exclusive. Weaver et al. proposes a mechanism through which mice have epigenetic programming by maternal behavior in the first week of life, with phenotypic expressions that persisted into adulthood. Applied to humans, it’s possible that there are parallel mechanisms through which maternal behaviors in the first hour or first week of a newborn’s life have implications for gene expression.
Gruenewald examines the way in which adversity across the life course of humans accumulates to affect the function of biological regulatory systems. This adversity could affect an adult’s HPA regulatory systems in addition to any maternal imprinting that occurred at birth or in early childhood.
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 give compelling examples of “gene-by-environment interactions,” wherein epigenetic processes early in life affect a person’s reactions to their environment throughout the life course. They describe experiments similar to Weaver’s that demonstrate that those programmed with a more sensitive flight-or-fight response have diminished sustained learning and memory functions over time. Early adversity, such as neglect from mother at birth, could lead to HPA axis functions that make it difficult for one to learn in school, to regulate emotions, etc, which, by chain reaction, can create disparities that only widen with time.