Abstract
Characteristic adaptations often cluster in mutually reinforcing networks. Evidence of stability and heritability suggests that the development of such networks is due in part to the causal influence of enduring dispositions or traits. Many different genetic models are consistent with this hypothesis, and the quest for genes can be pursued at many levels; of these, the intermediate level of specific facets may be the most promising. Published 2012. This article is a U. S. Government work and is in the public domain in the USA.
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