But, in speaking of a progress toward vision, are we not coming back to the old notion of finality? It would be so, undoubtedly, if this progress required the conscious or unconscious idea of an end to be attained. But it is really effected in virtue of the original impetus of life; it is implied in this movement itself, and that is just why it is found in independent lines of evolution. If now we are asked why and how it is implied therein, we reply that life is, more than anything else, a tendency to act on inert matter. The direction of this action is not predetermined; hence the unforeseeable variety of forms which life, in evolving, sows along its path. But this action always presents, to some extent, the character of contingency; it implies at least a rudiment of choice. Now a choice involves the anticipatory idea of several possible actions. Possibilities of action must therefore be marked out for the living being before the action itself. Visual perception is nothing else:[50] the visible outlines of bodies are the design of our eventual action on them. Vision will be found, therefore, in different degrees in the most diverse animals, and it will appear in the same complexity of structure wherever it has reached the same degree of intensity.
We have dwelt on these resemblances of structure in general, and on the example of the eye in particular, because we had to define our attitude toward mechanism on the one hand and finalism on the other. It remains for us to describe it more precisely in itself. This we shall now do by showing the divergent results of evolution not as presenting analogies, but as themselves mutually complementary.
FOOTNOTES:
[3] Matière et mémoire, Paris, 1896, chaps. ii. and iii.
[4] Calkins, Studies on the Life History of Protozoa (Archiv f. Entwicklungsmechanik, vol. xv., 1903, pp. 139-186).
[5] Sedgwick Minot, On Certain Phenomena of Growing Old (Proc. Amer. Assoc. for the Advancement of Science, 39th Meeting, Salem, 1891, pp. 271-288).
[6] Le Dantec, L'Individualité et l'erreur individualiste, Paris, 1905, pp. 84 ff.
[7] Metchnikoff, La Dégénérescence sénile (Année biologique, iii., 1897, pp. 249 ff.). Cf. by the same author, La Nature humaine, Paris, 1903, pp. 312 ff.
[8] Roule, L'Embryologie générale, Paris, 1893, p. 319.
[9] The irreversibility of the series of living beings has been well set forth by Baldwin (Development and Evolution, New York, 1902; in particular p. 327).