Let us consider first haw new forms of animal may originate from a common ancestor. When a member of the original species mover into a new environment, it is likely to evolve new features adapted to the new local conditions. Such geographical variations among animals are commonly found ; in the Galapagos, for instance, the lane birds other than finches vary from island to island, with only one form on each island these forms are not distinct species but subspecies, or geographical races, their differences, however. Are hereditary and not trivial or accidental . there are several examples of such geographical variation among Darwin’s finches. Three common species of the ground finch, for instance, are found on most of the islands; they are large, medium and small, feeding on large , medium and small seeds respectively. Now on two southern islands the large species is missing, and here the medium species has a rather larger beak than elsewhere presumably an adaptation to the large seeds available to it in the absence of the large species. Again, on another islet the small ground-finch is absent, and the medium species fills the gap by being rather smaller than. Elsewhere. on still other islets the medium species is missing and the small species rather larger than elsewhere.