Evolution, in the broad sense, is the sequential transformation of a system through time. Any theory of evolution, whether in the physical, biological, or cultural realms, requires units that undergo change through time as well as forces that cause these transformations. Bill Durham, in his recent synthetic tome Coevolution: Genes, Culture, and Human Diversity (1991), has suggested that basic color terms represent the best available example of the interactive mode of coevolutionary relationship between genes and culture that he calls “genetic mediation.” For Durham, “coevolution” describes the parallel action of cultural selection (i.e., preservation by preference advantage) and Darwinian natural selection (i.e., preservation by survival and reproductive advantage) in the evolution of human phenotypes. “Genetic mediation” is distinguished from four other modes of gene–culture coevolution, designated “cultural mediation,” “enhancement,” “neutrality,” and “opposition,” by its reliance on genetic differences as causal for the evolution of cultural differences.

According to Durham (1991), the relevant genotypes in the color term system are those responsible for the pigment-based system of light absorption in the eyes and for the neurophysiological processing of sensory input to the brain. The units of information or functional units of cultural transmission analogous to units of the genetic realm are the descriptive verbal labels for the experience of color. Differences in the cultural fitnesses within a set of color terms would, according to Durham's model, vary as a function of primary developmental values conditioned by genotype frequencies.