Vertebrate secondary sexual characteristics - Physiological mechanisms andevolutionary patterns

As most commonly presented, the organization-activation theory of sexual di fferentiation emphasizes the importance of the relative age of the organism for understanding steroid hormone effects. However, considering the actual physiological mechanisms of tissue enlargement (hyperplasia/hypertrophy) p rovides an additional perspective for interpreting patterns of evolutionary change in sexual dimorphism. Using that focus, it is possible to suggest m echanistic explanations for patterns of allometry and the size of some seco ndary sexual characteristics produced by "runaway" selection. It can also l ead to the formulation of testable hypotheses regarding the type of sexuall y dimorphic characters that might evolve through "good genes" models; the r elationship between intrasexual competition, polygyny, and the development and size of male weapons; and the control and type of secondary sexual char acteristics that will be present in males with associated and disassociated reproductive patterns.