Just as ensembles of traits may evolve, so may the system of inheritance that affects the expression of those traits. The evolution of readily observable traits such as body size, brain size, etc. is well understood from numerous studies. We know how rapidly (or slowly) such observable traits evolve. Basic evolutionary facts about systems of inheritance, however, are virtually unknown, despite their importance to modern evolutionary theory. We do not know how rapidly the inheritance system evolves. The system of inheritance for a set of observable traits is assessed by measuring the degree of resemblance between parents and their offspring for those traits. To assess the inheritance system of any particular population, we must measure resemblance in many sets of parents and offspring. The necessity of a large sample of relatives in each population or species has frustrated comparative studies of inheritance. The proposed project will use animals (garter snakes and water snakes) in which large samples of parents and their offspring can be readily assembled. These animals have the further advantage that evolutionary relationships are already known from biochemical work. Consequently, systems of inheritance can be compared among closely and distantly related species and rates of evolution can be determined. Modern evolutionary theory often assumes that systems of inheritance evolve so slowly that they are effectively invariant. The proposed project will constitute the first strong test of that critical assumption in natural populations of organisms.