Blair and Raver (2012) have provided an organism-in-environment conceptualization of the development of stress response physiology and its relation to the development of self-regulation. They argue that we must consider the context in which self-regulation and stress reactivity occur to understand their implications for developmental outcome. More generally, they present a cogent argument for why it is necessary to think developmentally when considering the effects of early experience on subsequent physical, emotional, cognitive, and social development. Blair and Raver's article also highlights a persistent challenge for developmental theory--how to make sense of the relationship among the various timescales over which phenotypes develop and change occurs. Their efforts to identify the factors involved in the variability and stability of self-regulation over different timescales demonstrate the dividends of integrating developmental and evolutionary perspectives to better understand the malleability of phenotypic development.