Control of genetics and phenotypic variability in quantative traits

Analysis of data on body weight of chickens showed there was genetic variation in the level of environmental (i.e. non-genetic) variation.
Theoretical analysis showed that:
1. Reduction of such variation by artificial selection to improve product uniformity is feasible, but requires large family sizes.
2. Evolutionary forces favouring intermediate phenotypes imply that environmental variation would be removed by natural selection.
3. Mechanisms to allow a stable level of variation to evolve were investigated; of these the most effective was a cost (engineering cost) to the organism of reducing variability, resource competition among individuals was ineffective, and evolution in fluctuating environments could be effective.