THE ORIGIN OF SPECIES 513 



virtue of the fact that it unifies and explains a number of lesser gener- 

 alizations, themselves for the most part established by direct induction, 

 in several special sciences. When, in these separate sciences, the sub- 

 sidiary generalizations underlying the theory of the transformation of 

 species were well established, and generally accepted by specialists, the 

 evidence for evolution must be said to have been logically complete. 

 This does not mean that more facts were not subsequently added; it 

 does mean that the argument was adequate without them, and that no 

 one who found the original evidence unconvincing had any logical 

 ground for being convinced by any of the considerations adduced in 

 the " Origin of Species " or in Huxley's earlier evolutionary writings. 



3. Argument from the Homologies in Vertebrates. — This argument 

 was, by 1844, already so old and even hackneyed a one, that it may, in 

 a consideration of the status of the evolutionary argument at that 

 special period, be passed over very briefly. The facts upon which the 

 argument rests had been in the possession of zoologists ever since Buffon 

 and Daubenton had laid the foundations of the science of comparative 

 anatomy (1749). These facts chiefly had, before the end of the eight- 

 eenth century, made evolutionists of Diderot, 21 of Kant, and (but for 

 perfunctory reservations in favor of religious orthodoxy) of Buffon 

 himself. It can, therefore, scarcely be necessary to cite evidence to 

 show that the argument was familiar a quarter of a century after the 

 whole conception of homologous organs had been clearly elaborated by 

 E. Geoffroy St. Hilaire. 22 Nor, for the purposes of the present paper, 

 is it necessary to estimate the precise logical weight of this argument 

 when it stands alone. At the time with which this inquiry is concerned, 

 it did not stand alone, but had been complemented by a number of con- 

 siderations more recently brought to light by scientific discovery. 



4. Argument from the Variability of Existing Species. — "Not less 

 old than the last-mentioned was the argument from the fact that exist- 

 ing — and, especially, domesticated — species have a marked tendency 

 to variation, exhibit an extensive diversity of form, and are capable of 

 transmitting variations to their descendants. It was mainly this 

 group of facts that had caused Maupertuis 23 to embrace the evolutionary 

 hypothesis before 1751. The same argument, with that from the homol- 

 ogies, is set down by Erasmus Darwin in the " Zoonomia," 1794, as 

 among the principal reasons for believing in the transformation of 

 species. We are led to such a belief, wrote the grandfather of the 

 author of the " Origin, 



a 

 -&*•• 



When we think of the great changes introduced into various animals by- 

 artificial or accidental cultivation, as in horses, ... or in dogs, ... or in the 



21 Cf. Lovejoy, "Some Eighteenth Century Evolutionists," The Popular 

 Science Monthly, August, 1904, pp. 323-327. 

 22 In his "Philosophic Anatomique," 1818. 

 23 Cf. Lovejoy in The Popular Science Monthly, July, 1904. 

 vol. lxxv. — 34. 



