Fig. 5. Peak shift model for the evolution of the colour patch in male house finches, following published descriptions (Hill, 1993; Hill, 1994b). The Michigan population (1) is inferred to be ancestral, with a large red patch (see Fig. 4). Establishment in Mexico is thought to have resulted in fewer carotenoids in the diet, resulting in a large pale patch as a phenotypically plastic response (2; see Fig. 2). Subsequent selection to increase patch brightness resulted in genetic evolution of small patch size (3) as in the Mexican population (Fig. 4).