1. I do believe that there is time sensitivity for specific development periods in humans. At its earliest, infant exposure to parental touch, being held and being feed by bottle or breast may be analogous to the “maternal licking and grooming” of rats. However, later childhood has other important developmental milestones which may also be time and stress sensitive, such as early socialization with other children which may be impacted by parental behavior and modeling. When first beginning socialization (i.e. preschool age) a child exposed to fear, violence or isolation at home is likely to have more difficulty forming social relationships than one exposed to a calm and nurturing home and this effect may last through to adulthood.
2. I would look for a natural experiment, such as differences in state funding or policies supporting maternal/child health to examine this question. One great example would be San Francisco’s recent approval of 6 weeks of paid parental leave for both parents which was passed under the hypothesis that increased early bonding between parents and children would be good for the children (http://www.sfgate.com/politics/article/Historic-SF-parental-leave-law-kicks-in-10831209.php) . We could recruit a cohort of parent/infant triads in San Francisco from a variety of income strata and a matched cohort from a city with similar demographics but no parental leave law also stratified by income and compare outcomes of childhood language, cognitive, motor, behavioral, and social-emotional milestones at regular intervals over the first 5 years of life. It would be important to include different income strata in the study, as high income families might take unpaid leave even without the law, while low income families may not have been able to afford the leave prior to the law.
3. I think the two focuses, Weaver’s focus on of the impact of maternal behavior and Gruenewald’s focus on cumulative effects of adversity/stress are consistent and not mutually exclusive. Both authors conclude that historical exposures (whether it be maternal behaviors or the host of measures in the MIDUS study) have measurable effects on health later in life, it may even be that parental factors illustrated by Weaver potentiate the later stressors/adversity measured by Gruenewald.
4. I agree with Hertzmann and Boyce that the existence of gradients in health which correspond to hierarchy in privilege is not in doubt in our current era. The evidence for epigenetic regulation being one pathway that explains how environmental gradients impacts genes and later health is convincing and I think that GxE interactions contribute greatly to health disparities across the dimensions. I believe there are also purely environmental determinants that influence developmental trajectories independent of genetics, for example lead exposure which occurs far more commonly in children in low income communities due to socio-political funding and governmental decision-making.