always lagged behind the physical sciences. This is attributable in large measure, of course, to the greater complexity of organic phenomena, but I suspect that the fact that animals and plants admit of an arrangement in generic and specific categories, which seem at first sight to be in singular harmony with the spirit of ancient science and philosophy, may be to a considerable extent responsible for the stolid conservatism of systematic biology. At a time when the physical sciences, through the labors of Kepler, Gallilei and Newton, had already become modern sciences in the true sense of the word, biology was still practically in the Greek stage. This is certainly true of zoology and botany proper up to the middle of the last century, although zoology had through medicine contracted some of the modern spirit, since by that time anatomy and physiology had definitively abandoned Greek and scholastic methods.
At this juncture appeared Darwin's "Origin of Species." The effect of this work was in the first instance destructive, for it tended to dissolve and mobilize the rigid conceptual schematism that dominated, not only the zoology and botany, but the whole cosmology of the time. The conception of an evolution which melted all living beings, man included, into a single vital stream, surging on into the future as it has surged through the æons of the past, continually creating new and destroying old forms, could not fail to clash with the conception of a world created once for all and since engaged very largely in marking time. According to the old view, living objects are more or less vitiated Platonic ideas or Aristotelian forms, according to the new they are eddies or whirlpools in a living current that modify and regulate their movements according to the obstacles, i. e., the "environment" which they encounter. No wonder men like Cuvier declined to accept the doctrine of evolution when it was first promulgated by Lamarck, and that von Baer and Louis Agassiz regarded its rehabilitation by Darwin as a heresy. All of these men believed in the existence of permanent types of organic structure, which, after all, were merely Platonic ideas parading under assumptions more or less theological, privileged moments or aspects of animal and plant morphology interpreted as thoughts of the Deity. It is quite unnecessary to mention the innumerable scholastic and theological opponents of evolution. Their animosity certainly had and still has other motives than a predilection for the Mosaic account of creation.
It is far pleasanter to contemplate the constructive aspects of Darwin's work. Since evolution, as conceived by him, admitted of a mechanical explanation—for survival through natural selection is mechanical and not teleological like survival through psychical effort as postulated by Lamarck—it breathed the spirit of the physical sciences and therefore allied itself with these rather than with psychology and