History of Comparative Anatomy 341 



clature" which is now universally used in classification. Any plant or 

 animal is identified by two names (in Latin), one indicating the larger 

 group, Genus, to which it belongs and the second the subdivision or 

 Species of that group. 



It was Buffon who revived Aristotle's idea of a "scala naturae" up 

 which living things have continuously progressed from "lower" to 

 "higher" or more nearly "perfect" forms. But Buffon seems to have 

 been hesitant about carrying the idea of genetic continuity to its logical 

 conclusions. Erasmus Darwin accepted the idea much more whole- 

 heartedly. Having a poetic bent, he set forth his scientific and philo- 

 sophic ideas in verse. The following lines are from his "Temple of 

 Nature." 



Hence without parents, by spontaneous birth, 

 Rise the first specks of animated earth. 



Organic life beneath the shoreless waves 

 Was born and nurs'd in ocean's pearly caves; 

 First, forms minute, unseen by spheric glass, 

 Move on the mud, or pierce the watery mass; 

 These, as successive generations bloom, 

 New powers acquire and larger limbs assume; 

 Whence countless groups of vegetation spring, 

 And breathing realms of fin and feet and wing. 



It remained for Lamarck to develop the idea of genetic continuity 

 into a well-organized Theory of Evolution. He pointed out that the 

 ascent of "Life" from nonliving to Man is not adequately represented 

 by a "scala." It is not a "ladder" that "Nature" has climbed, but a 

 tree, produced in the process of climbing — a tree of numerous branches, 

 larger and smaller, and innumerable terminal twigs. He offered a clearly 

 formulated causal explanation of the process of evolution. The reac- 

 tions of an organism to its environment produce structural changes in 

 the organs concerned and the changes thus acquired are transmitted to 

 the offspring — "inheritance of acquired characters." Vigorous use of an 

 organ tends to strengthen it and perpetuate it in the race; disuse is 

 attended by atrophy of the organ. Very similar ideas had been ex- 

 pressed, but less fully worked out, by Erasmus Darwin. This causal 

 theory, as offered by Darwin and Lamarck, seemed attractively plaus- 

 ible and reasonable. Biology has been reluctant to reject it in spite of 

 the fact that the century and a half since Lamarck has yielded no con- 

 vincing evidence that "acquired characters," in the sense of Lamarck's 

 theory, can be inherited. Nevertheless Lamarck must be credited with 

 having laid out the main lines of the modern Theory of Evolution. His 

 study of fossil invertebrates was of special importance. 



