Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/185

Rh race, when subjected to more favorable conditions, in becoming more civilized, begin to resemble those more advanced,—considering these facts together, the view might be suggested to the Ethnologist that the different races had come from one stock. An important fact to be remembered in reference to the origin of races is that peculiarities which appear in the parent reappear in the offspring at the same age in which the parent was affected. Thus, the parent at a certain age develops a disease: his child grows up apparently healthy; suddenly the same disease appears in the child, and at the same age at which the parent was affected. Though the causes of peculiarities appearing in the parent, and the inheriting of them by the offspring, are still unknown, or very obscure, nevertheless we know it to be a fact that peculiarities—good or bad—affecting a parent may, and often do, reappear in the offspring in the manner just illustrated. Suppose, now, in a remote past, two animals, the descendants of the same parent, grew for some time alike, but that gradually they began to differ, acquiring certain peculiarities. These, if transmitted to posterity, would appear at the same age in which they were acquired by the parents. This hypothetical case illustrates what we suppose to have been the development of the Bird and Mammal from a common ancestor, the Reptile. This reptilian ancestor had two descendants; one acquired the peculiarities of the Bird, the other those of the Mammal: the Bird and Mammal of the present day ought, therefore, to develop in a reptilian manner until they attain the age at which their progenitors acquired the characteristic of the Bird and Mammal; from that time their development ought to be different. Our brief résumé of development shows that the facts perfectly confirm such a theory. By the same reasoning we conclude that the Reptiles and Batrachia have diverged from a form like that of the Lepidosiren, or Mud-fish, the Bony