Phenotypic, Genetic, and Environmental Morphological Integration in the Cranium

Modern theories of evolutionary change have stressed the unity of the genotype (Mayr, 1963, 1976; Lewontin, 1974; Wright, 1978, 1980). is the total phenotype which is selected upon and the total genotype which evolves rather than individual phenotypic characters or genes. Individual phenotypic characters and genes only evolve within the larger context of the organism in which they occur. Therefore, organisms are the integrated functional units which evolve. This outlook on evolutionary change lends itself to a holistic, systems view of an organism (Waddington, 1957; Riedl, 1978; Gould and Lewontin, 1979). Mayr (1976) refers to the unity of the genotype because most phenotypic characters are the result of the collaboration of many structural and regulatory genes. Most traits of evolutionary importance are polygenic (Lewontin, 1974). Also, most genes are pleiotropic, affecting many different aspects of the phenotype (Wright, 1980). Mayr states, It is no longer possible to regard the phenotype as a mosaic in which each part can be replaced without any effect on neighboring components . . . (also) the genotype is an organic whole with an internal harmony that, when exposed to a new selection pressure, will change . . . in a harmonious manner (1976, p. 49). Both genotype and phenotype are systems composed of interacting components.