a longstanding tension within agricultural research between, broadly speaking, breeders and physiologists. Breeders seek improvement through selection of varieties combined with plant or animal husbandry appropriate to those varieties. Physiologists focus on determining and manipulating the specific genetic and environmental factors underlying the development of the trait in question. (In this era of genomics, breeders may also be physiologists, but let [us] continue distinguishing the two ideal types.) Breeders are not uninterested in the underlying factors. They make hypotheses about such factors based on… trials [of multiple varieties grown in multiple locations] as well as sources other than the data analysis, then use these hypotheses to plan the next set of varieties and locations on which to collect data… Physiologists make much less use of variety-location trials to generate hypotheses; instead they focus on experiments under controlled conditions. Since the advent of DNA technologies, their experiments have included modification of specific genetic factors.
The question that arises is whether the factors that are important under the controlled conditions also apply more broadly…? If not, the controlled conditions have to be prescribed and replicated in actual plant or animal husbandry. The breeder is not so constrained. Even in the absence of realistic models of the underlying factors and even if those factors are heterogeneous, it is sometimes possible that progress through selection and mating can be made…. Breeders can compensate for any less-than-expected progress from one generation to the next by continuing selective breeding for more generations… Physiologists… want to design experiments around genetic and environmental factors that are likely to be important influences on the trait being studied…
How does this breeder-physiologist tension play out for human heritability studies? After all, controlled mating and selection is not possible, nor are trials based on each of a set of varieties raised in each of a set of locations… On the physiologist side, there are obviously serious limits to the use of experiments to determine and manipulate the specific genetic and environmental factors underlying the development of human traits…
The quotes above are from page 101ff in Taylor, Peter J. (2014) Nature-Nurture? No: Moving the Sciences of Variation and Heredity Beyond the Gaps.
(Introduction to this series of posts)