Page:Popular Science Monthly Volume 39.djvu/607

Rh so many people mix up Darwinism with the doctrine of evolution, and have but the vaguest and haziest notions as to what it is all about. As I explained above, Mr. Darwin's great work was the discovery of natural selection and the demonstration of its agency in effecting specific changes in plants and animals; and in that work he was completely original. But plants and animals are only a part of the universe, though an important part, and with regard to universal evolution or any universal formula for evolution Darwinism had nothing to say. Such problems were beyond its scope.

The discovery of a universal formula for evolution, and the application of this formula to many diverse groups of phenomena, have been the great work of Mr. Spencer, and in this he has had no predecessor. His wealth of originality is immense, and it is unquestionable. But as the most original thinker must take his start from the general stock of ideas accumulated at his epoch, and more often than not begins by following a clew given him by somebody else, so it was with Mr. Spencer when about forty years ago he was working out his doctrine of evolution. The clew was not given him by Mr. Darwin. Darwinism was not yet born. Mr. Spencer's theory was worked out in all its parts, and most parts of it had been expounded in various published volumes and essays before the publication of The Origin of Species.

The clew which Mr. Spencer followed was given him by the great German embryologist Von Baer, and an adumbration of it may perhaps be traced back through Kaspar Friedrich Wolf to Linnæus. Hints of it may be found, too, in Goethe and in Schelling. The advance from simplicity to complexity in the development of an egg is too obvious to be overlooked by any one, and was remarked upon, I believe, by Harvey; but the analysis of what that advance consists in was a wonderfully suggestive piece of work. Von Baer's great book was published in 1829, just at the time when so many stimulating ideas were being enunciated, and its significant title was Entwickelungsgeschiclite, or History of Evolution. It was well known that, so far as the senses can tell us, one ovum is indistinguishable from another, whether it be that of a man, a fish, or a parrot. The ovum is a structureless bit of organic matter, and in acquiring structure along with its growth in volume and mass, it proceeds through a series of differentiations, and the result is a change from homogeneity to heterogeneity. Such was Von Baer's conclusion, to which scanty justice is done by such a brief statement. As all know, his work marked an epoch in the study of embryology, for to observe and mark the successive differentiations in the embryos of a thousand animals were to write a thousand life-histories upon correct principles.

Here it was that Mr. Spencer started. As a young man he was