Evolutionary mechanisms for beak shape diversity in Darwin’s finches (Thraupidae, Passeriformes). (A) Molecular phylogeny of 14 species of Darwin’s finches shows a range of beak shapes in this group of birds. These species have beaks of different shapes that allow them to feed on many different diets: insects, seeds, berries, and young leaves. Species are numbered as follows: small ground finch Geospiza fuliginosa; medium ground finch G. fortis; large ground finch G. magnirostris; cactus finch G. scandens; large cactus finch G. conirostris; sharp-billed finch G. difficilis; small tree finch C. parvulus; large tree finch Camarhynchus psittacula; medium tree finch C. pauper; woodpecker finch C. pallidus; vegetarian finch Platyspiza crassirostris; Cocos finch Pinaroloxias inornata; warbler finch Certhidea fusca; warbler finch C. olivacea (phylogeny from ). (B1) Large ground finch (left) has a very deep and broad bill adapted to crack hard and large seeds, while the cactus finch (right) has an elongated and pointy beak for probing cactus flowers and fruits. (B2) Geospiza finch bills develop their distinct shapes during embryogenesis and are apparent upon hatching (mid-development stage 35 embryos are shown from Abzhanov et al.). (B3) The cactus finch-specific expression of CaM was validated by in situ hybridization after it was identified as a candidate by a microarray screen .