Thanks Hala. The cumulative effects model, if true, is very important because it suggests we can still substantially offset early life harm via adult interventions. The critical period model suggests once the window is closed, there is little to be done. This debate has informed much recent emphasis on early childhood interventions - because a major argument from Heckman and others has been that adult social interventions appear to have little to no effect, in contrast to interventions ages 3-5. Epigenetic patterns do change in adulthood but much much less than in early life. Epigenetic erasure/rewriting is highly regulated biologically with respect to developmental timing, so it's possible that action really has to be in early life and everything later is unlikely to have large effects.
Maria