“Heredity, Environment, and the Question “How?””, 1958 (; backlinks):
…A more fruitful approach to the heredity-environment problem is the question. “How?” in place of “Which one?” and “How much?”
Promising lines of research are: selective breeding of animals with inbred behavioral differences, relations between physiological variables and individual behavioral differences, the role of prenatal physiological factors, the effect of early experience upon future behavioral characteristics, cultural differences in child-rearing, mechanisms of somatopsychological relationship, and twin studies from infancy to maturity.
…Such approaches are extremely varied with regard to subjects employed, nature of psychological functions studied, and specific experimental procedures followed. But it is just such heterogeneity of methodology that is demanded by the wide diversity of ways in which hereditary and environmental factors interact in behavior development.