Serial Homology is that unity of type which is found on comparing the different parts and organs in the same individual. The complex and varied jaws and legs of a lobster, or the different leaves, sepals, petals, stamens and pis tils of a flower are all found to be modifications of a simple leaf-organ respectively. Not only are such metamorphoses apparent on compari son, but they can be actually observed during the development of each individual. So closely do the embryos of the most distinct species be longing to the same class resemble each other, that even Von Baer was unable to decide whether two unlabeled specimens were lizards, birds or mammals. The process of development 'goes from the general to the special; thus there is generally an advance in organization. In pe culiar conditions degeneration may occur. All these facts are explained on the principle of suc cessive slight variations not necessarily or gen erally supervening very early in life and in herited at a corresponding period; hence it is in the highest degree probable that most embryonic stages show us more or less completely the pro genitor of the group in its adult state; and em bryology thus rises greatly in interest. Darwin points out that the theory of evolution by natu ral selection is no more inimical to religion than is that of gravitation, to which the same ob raised. Since the researches of the last two decades on heredity (q.v.) have brought to light the fact that variations are not in gen eral infinitesimal, but. are in general rather of the nature of mutations, the discussion of natural selection has entered on a new stage, The periods which were formerly believed to be essential for the differentiation of a species have been shown to be far too large. On the
other hand, the problem how a series of what are apparently arbitrary jumps can lead to the development of such a perfectly adapted organ as a wing is exceedingly difficult to explain, more particularly as it appears that the number of mutations of which an organism is capable, though great, is predetermined in the chromo somes (q.v.) of its cells. This fact has led Certain biologists to have recourse to the theory of the inheritance of 'acquired characteristics, which, indeed, was not foreign to the views of Darwin. The weight of evidence, however, seems to oppose this theory. See Evoiarnox, THEORIES or; HEREDITY; GENETICS.
Dewar, D., & Finn, F., 'The Making of Species' (London 1909) ; 'Fifty Years of Darwinism: Modern Aspects of Evolu tion' (New York 1909); Fiske, J., 'Darwinism and Other Essays' (Boston 1888) ; Kellogg, V. I.., 'Darwinism To-Day' (New York 1908) ; Romans, G. J., 'Darwin and After Darwin' (London 1893-97) ; Schmidt, E. O., 'The Doc trine of Descent and Darwinism' (London 1891) ; Schurman, J. G., The Ethical Import of Darwinism' (New York 1893) ; Spiecker mann, A., 'Has Darwinism Played Out?' (Gettysburg, Pa. 1908); Thomson, J. A., 'Dar winism and Human Life' (New York 1910) ; Wainwright, L., 'Scientific Sophisms (New York 1883); Wallace, A. R. 'The Present Posi tion of Darwinism' (London 1908) ; Stallcup, J. S., 'A Refutation of the Darwinian. Concep tion of the Origin of Mankind' (Tacoma 1913).