ONE of the first insights into the origin of species was the case of Darwin’s finches. Actually, they are not finches, but members of another avian group, the tanagers. But the pertinent point is that these birds, which live on the Galapagos Islands and were first made known to science in the 1830s, by Charles Darwin, have different-shaped beaks adapted to different food stuffs even though they all seem to be descended from the same South American ancestor. Some spear insects with thin, sharp beaks. Some have heavy, blunt beaks for cracking seeds open. Some, of intermediate beak geometry, peck at cactuses. One has even worked out how to use cactus spines to extract insect grubs from rotten wood.