THE EFFECT OF EXTERNAL INFLUENCES UPON DEVELOPMENT
Nägeli's conception with regard to the evolution of the organic world I have always regarded as a surprising one. He supposed that it had originated in virtue of inherent internal forces, and that extemal influences had co-operated only secondarily and unessentially,—improving and modifying, but not determining. This acute thinker stated plainly that in his opinion the course of development would, on the whole, have resulted pretty much as it has done, even if the conditions of life had remained unchanged from the earliest times.
I do not mention this view in order to criticize it, having already done so long since: at the present day there are probably few naturalists who adhere to it. It was in a sense a last effort to save at least a remnant of the abandoned 'creation-hypothesis,' a motive force being ascribed to organisms, instead of their development being deduced from the interaction of external and internal forces—that is, from the action of the outer world upon the organism.
