Fig. 4.

Average CVs of beak length for male specimens of each species of Darwin’s finches in relation to their ages. Points fitted by nonlinear, polynomial regression: peak, Gaussian, and 4 parameters. The adjusted R² value is 0.23. Included are 2 pairs of populations, Certhidea fusca from Española and San Cristóbal and Geospiza septentrionalis from Wolf and Darwin. These are the only pairs of conspecific populations with estimated ages of independence (40). Morphological data are from ref. 41. The curve for beak depth variation is almost identical.