the insights that are being gleaned from twin and adoption studies and expect that they will provide further stimulus and insights. The novel analysis of time trends in the partitioning of components of genetic and shared-environment variance components is replicable with long-term demographic registers given modern computer linkage algorithms. But the longer-term horizon demands molecular linkages, especially if the partners are both to be considered.
Demographers concerned with such issues (and we all should be) will have to think carefully about the design of studies in order to tease out the complexities involved and most of the advances will involve learning from or engaging with molecular geneticists, brain scientists, and endocrinologists. Demographers also need to understand and work more closely with the broader interpretative disciplines rooted in evolutionary perspectives. The research agenda is an exciting one in which rapid scientific progress needs a strong social scientific perspective and vice versa. Exemplified by the National Research Council and Institute of Medicine (2000) and National Research Council (2001) and by the present volume, this recognition of the need to collaborate across disciplinary boundaries is gradually occurring in a range of fields.
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