Introduction

Abstract

The history of domestication of animals and plants, and the selective breeding of the enormous variety of animals and plants for aesthetic purposes, attests very clearly to the presence of genetic variation within species. This has been demonstrated further by numerous common garden experiments in which individuals from different populations are grown under the same set of conditions [Table 1.1; note that nongenetic, maternal effects require that the populations pass at least two generations under the common garden conditions; see Nelson et al. (1970), Baskin and Baskin (1973), Quinn and Colosi (1977)]; differences between populations are almost invariably found. These differences occur in traits that vary continuously (Table 1.1) or show discrete variation [e.g., diapause propensity, wing dimorphism in insects, dimorphism in “weaponry,” behavioral dimorphisms; see Roff (1996a) for a review] that cannot be reconciled with simple Mendelian models (e.g., single locus with two alleles).