Inferring and Explaining

72 InferrIng and exPlaInIng the New—at least as closely as same species generally require. . . . Not withstanding this general parallelism in conditions of the Old and New Worlds, how widely diferent are their living productions! 7 From continents separated by whole oceans to islands separated by just a few miles of ocean, themicroquestions of biogeographical distribu- tion are just as puzzling on the theory of special creation. Te same law which has determined the relationship between the inhabitants of islands and the nearest mainland, is sometimes displayed on a small scale, but in a most interesting manner, within the limits of the same archipelago. Tus each separate island of the Galapagos Archipelago is tenanted, and the fact is a marvelous one, by many distinct species; but these species are related to each other in amuch closer man- ner than to inhabitants of the American continent, or any other quarter of the world. 8 Descent with modifcation, of course, beau- tifully answers both questions. Te fora and fauna in the Old and New Worlds are generally diferent because they spring from very difer- ent lines of descent. Species in the Galapagos (think of his famous fnches) all descend from a common ancestor on the South Americanmain- land but have diferent histories of descent on the individual islands. Morphological Facts Morphology is the science of shape and form, hence the computer notion of an image “mor- phing.” Consider the following four tetrapods. Why the common four-“leg” structure? Te frog hops, the lion runs, this particular dinosaur swam, and the bird fies. If youwere engineering a hoppingmachine, a runningmachine, a swim- ming machine, and a fying machine, would you automatically use the same overall design? Darwin saw morphology as fundamental to his defense of descent with modifcation. We have seen that the members of the same class, independently of their habits of life, resemble each other in the general plan of their organization. Tis resemblance is ofen expressed by the term “unity of type” . . . Te whole subject is included under the gen- eral name of Morphology. Tis is the most interesting department of natural history, and may be said to be its very soul. 9 fIgure 3. Frog, lion, dinosaur, and hawk Retrieved from https://www.fickr.com/x/t/ 0094009/photos/aspidoscelis/31098104412/, https://www.fickr.com/x/t/0097009/photos/ mathiasappel/26260010225/, https:// www.fickr.com/x/t/0093009/photos/ internetarchivebookimages/14777663574/, and https:/ /www.fickr.com/ x/t/0098009/ photos/priyanthadealwis/29599225312/ (respectively).