The nature versus nurture distinction, while traditional, is obsolete. The modern literature on epigenetic expression and gene-environment interactions shows that the sharp distinction between acquired skills and ability featured in the early human capital literature and that still guides much research in health economics (Grossman 1972, 2000) is not tenable (Pray 2004, Rutter 2006). Additive "nature" and "nurture" models, while traditional and still used in many studies of heritability and family influence, mischaracterize how ability and health are manifested. Genes and environment cannot be meaningfully distinguished by traditional linear models that assign unique variances to each component. Abilities are produced, and gene expression is governed, by environmental conditions (see Rutter 2006). Measured abilities are the outcome of environmental influences, including in utero experiences, and also have genetic components.

Behaviors and abilities have both a genetic and an acquired character. Recent analyses in economics that break the "causes" of birthweight into environmental and genetic components ignore the lessons of the recent epigenetic and gene-environment literatures, and provide misleading guides to policy because they suggest the operation of "genetic" factors are beyond the scope of policy intervention. We seek to expand our studies beyond the United States by using the data to address the following:

(1) What environmental (parental, neighborhood) inputs affect health, cognition and socioemotional skills at different stages of childhood? What are the critical and sensitive periods for remediation?

(2) How do these stocks of capacities cross-fertilize each other? How effective are socioemotional and cognitive interventions on health and its evolution? How do health stocks cross-fertilize socioemotional and cognitive skill production?

(3) What are the costs and the benefits of interventions for remediation and prevention at different stages of the lifecycle of children?