My Year of Darwin 5/21/2014: There's something about those finches...

 

"The most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and (if Mr. Gould is right in including his sub-group, Certhidea, in the main group) even to that of a warbler. The largest beak in the genus Geospiza is shown above in Fig.1, and the smallest in Fig. 3; but instead of there being only one intermediate species , which a beak of the size shown in Fig 2, there are no less than six species with insensibly graduated beaks"  Charles Darwin, Voyage of the Beagle