Figure 1.

Example responses of 2 populations (A and B) to selection on 2 traits (x and y). In both populations, the optimum is located at x = 0, y = 0, both populations start with the same trait means (−11, 5), selection occurs over 1,000 generations, and the strength of selection is the same for both populations. Plotted in both A and B are the bivariate distributions (solid ellipse), the change in populations means in response to selection (solid line), and the fitness landscape (dashed gray lines). Population means in 100 generation steps are plotted as small open circles along the response trajectory. In population A, the 2 traits are positively but weakly correlated (r = 0.15). In population B, the two traits are positively and more strongly correlated (r = 0.75).