The case of the hind limb vestiges in the various species of whales may be emphasized as a crucial one. Several different degrees of rudimentation are found in different types of whales, ranging from a state in which the pelvic bones and those of most of the leg clearly recognizable as such down to one in which these bones are entirely absent in the adult condition. In the cases where the bones are obvious, the situation is just this—deeply buried beneath the thick cushion of blubber in the pelvic region there lies a little handful of bones, ridiculously minute in comparison with the giant proportions of the other parts of the skeleton. These bones are immovable because their muscular connections are atrophied; they do no service in supporting the frame of the animal; in short, they cannot possibly function as bones at all. The somewhat puerile argument of the antievolutionist that these vestigial limb bones play some useful, though unknown role, else they would never have been created, cannot seriously be entertained in this case, for what can they make of the fact that some whales entirely lack these structures? More difficult even than this for the special creationist to explain is the fact that, even in these whales that lack vestigal limb bones in the adult condition, posterior limb buds appear in the early embryonic period and then slowly atrophy. The case just described in in no way exceptional or peculiar. It is, on the contrary, quite typical of a very general phenomenon.
Vestigal Structures in Man.
There are, according to Wiedersheim, no less than 180 vestigal structures in the human body, sufficient to make of a man a veritable walking museum of antiquities. Among these are the vermiform appendix, the abbreviated tail with its set of caudal muscles, a complicated set of muscles homologous with those employed by other animals for moving their ears, but practically functionless in all but a few men; a complete equipment of scalp muscles used by other animals for erecting the hair, but of very doubtful utility in man even in the rare instances when they function voluntarily; gill slits in the embryo the homologues of which are used in aquatic respiration; miniature third eyelids (nictitating membrane), functional in all reptiles and birds, greatly reduced or vestigial in all mammals; the lanugo, a complete coating of ebryonic down or hair, which disappears long before birth and can hardly serve any useful function while it lasts. These and numerous other structures of the same sort can be reasonably interpreted as evidence that man has descended from ancestors in which these organs were functional. Man has never completely lost these characters; he continues to inherit them though he no longer has any use for them. Heredity is stubborn and tenacious, clinging persistently to vestiges of all that the race has once possessed, though chiefly concerned in bringing to perfection the more recent adaptive features of the race.
Homology Versus Analogy.
It is quite common to find different animals with certain structures that look alike and function alike, but are not homologous. The eye of the octopus; a cepaloped mollusk, has a chorion, a lens, a retina, an optic nerve, and a general aspect decidedly like that of a fish. As an optical instrument it must obviously function in the same manner as does the eye of an acquatic vertebrate; but not one part of the eye of a cephalopod is homologous with that of a vertebrate. Because those two types of eye look alike and function alike, but arise from quite different embroyonic primodin adapted to meet a common function, they are known as analogous structures. They are to be sharply contrasted with homologous structures, which may be widely different in form and function so long as they arise from equivalent embryonic primordic. Both homologies and analogies imply changes in relation to the environment, and, therefore plainly favor the idea of descent with modification.
