Stabilizing selection and metabolism.

This paper attempts to provide a biochemical explanation for selection against extreme phenotypes. From current ideas on the analysis of metabolic control, it is argued that, on average, most mutations will reduce flux through metabolic pathways and change substrate pool concentrations in an arbitrary direction. Currently available experimental data suggests that there may be a positive relationship between flux and fitness. It is also argued that there may be a relationship between phenotypic traits and substrate pool concentrations. Given these premises, it is shown that intrinsic selective constraints occur against the production of extreme phenotypic variants.