The great problem which has so long exercised the minds of naturalists, namely, that concerning the origin of different kinds of animals and plants, seems at last to be fairly on the road to receive—perhaps at no very distant future—as satisfactory a solution as it can well have.

But the problem presents peculiar difficulties. The birth of a “species” has often been compared with that of an “individual.” The origin, however, of even an individual animal or plant (that which determines an embryo to evolve itself,—as, e.g., a spider rather than a beetle, a rose-plant rather than a pear) is shrouded in obscurity. A fortiori must this be the case with the origin of a “species.”

Moreover, the analogy between a “species” and an “individual” is a very incomplete one. The word “individual” denotes a concrete whole with a real, separate, and distinct existence. The word “species,” on the other hand, denotes a peculiar congeries of characters, innate powers and qualities, and a certain nature realized indeed in individuals, but having no separate existence, except ideally as a thought in some mind.

Thus the birth of a “species” can only be compared metaphorically, and very imperfectly, with that of an “individual.”

Individuals as individuals, actually and directly produce and bring forth other individuals; but no “congeries of characters” no “common nature” as such, can directly bring forth another “common nature,” because, per se, it has no existence (other than ideal) apart from the individuals in which it is manifested.