Paleontology.
Experimental Breeding or Genetics.
The Evidence from Comparative Anatomy
When we study animals and plants we find that they can be arranged in groups according to their resemblances. This is the basis of comparative anatomy, which is only an accurate study of facts that are superficially obvious to everyone.
The groups are based not on a single difference, but on a very large number of resemblances. Let us take for example the group of vertebrates.
Fig. 3. Limb skeletons of extinct and living animals, showing the homologous bones: 1, salamander; 2, frog; 3, turtle; 4, Aetosaurus; 5, Pleisiosaurus; 6, Ichthyosaurus; 7, Mesosaurus; 8, duck. (After Jordan and Kellogg.)
The hand and the arm of man are similar to the hand and arm of the ape. We find the same plan in the forefoot of the rat, the elephant, the horse and the opossum. We can identify the same parts in the forefoot of the lizard, the frog (fig. 3), and even, though less certainly, in the pectoral fins of fishes. Comparison does not end here. We find similarities in the skull and back bones of these same animals; in the brain; in the digestive system; in the heart and blood vessels; in the muscles.
Each of these systems is very complex, but