CHAPTER X 
EVIDENCES FROM MORPHOLOGY 
(COMPARATIVE ANATOMY): 
GEORGE JOHN ROMANES 
The theory of evolution supposes that hereditary characters 
admit of being slowly modified wherever their modification will render 
an organism better suited to a change in its conditions of life. Let 
us, then, observe the evidence which we have of such adaptive modifi- 
cations of structure, in casés where the need of such modification is 
apparent. We may begin by again taking the case of the whales and 
porpoises. The theory of evolution infers, from the whole structure 
of these animals, that their progenitors must have been terrestrial 
quadrupeds of some kind, which gradually became more and more 
aquatic in their habits. Now the change in the conditions of their 
life thus brought about would have rendered desirable great modifica- 
tions of structure. These changes would have begun by affecting the 
least typical—that is, the least strongly inherited—structures, such 
as the skin, claws, and teeth. But, as time went on, the adaptations 
would have extended to more typical structures, until the shape of 
the body would have become affected by the bones and muscles 
required for terrestrial locomotion becoming better adapted for 
aquatic locomotion, and the whole outline of the animal more fish-like 
in shape. This is the stage which we actually observe in the seals, 
where the hind legs, although retaining all their typical bones, have 
become shortened up almost to rudiments, and directed backwards, 
so as to be of no use for walking, while serving to complete the fish-like 
taper of the body (Fig. 11). But in the whales the modification has 
gone further than this so that the hind legs have ceased to be apparent 
externally, and are only represented internally—and even this only 
in some species—by remnants so rudimentary that it is difficult to 
make out with certainty the homologies of the bones; moreover, the 
head and the whole body have become completely fish-like in shape 
(Fig. 12). But profound as are these alterations, they affect only 
t From G. J. Romanes, Darwin and after Darwin (copyright 1892). Used by 
special permission of the publishers, The Open Court Publishing Company. 
129 
