Page:Popular Science Monthly Volume 50.djvu/844

822 to case, till men whom no power of abstract argument could convince were convinced by pure force of successive witnesses. They were borne down by numbers. Your ordinary Englishman, indeed, is never quite satisfied by Euclid's demonstration that in a right-angled triangle the square on the hypotenuse is equal to the sum of the squares on the two opposite sides; he honestly believes it when he sees it tried a hundred and twenty times by careful measurement, and still more when he finds that engineering works which take it for granted as a basis succeed in paying a satisfactory dividend. Proof that in the nature of triangles this truth is involved he does not regard; experimental verification, or what seems to be such, in a few concrete cases, amply satisfies him. Hence it came about that a world which would have listened coldly to Herbert Spencer's a priori reasonings or splendid generalizations was converted at once when Darwin brought up with inexhaustible patience and extraordinary keenness of insight his profound array of confirmatory facts about bees and cuckoos, about the fertilization of orchids and the movements of tendrils.

Nobody has better summarized than Mr. Clodd the exact point which evolutionary theory had reached as regards plants and animals before the publication of The Origin of Species. Whoever wishes to learn just how much was surmised by the predecessors of Darwin, and just how much Darwin added to their ideas, can not do better than consult his luminous exposition.

Once, indeed, no less than seven years before the publication of The Origin of Species, Mr. Spencer even trembled for a moment on the verge of the actual discovery of natural selection. This was in the essay on population in the Westminster Review in 1852. The passage at full is too long to extract; but I will quote the last words of it. "All mankind subject themselves more or less to the discipline described; they either may or may not advance under it; but in the nature of things only those who do advance under it eventually survive. For, necessarily, families and races whom this increasing difficulty of getting a living which excess of fertility entails does not stimulate to improvements in production . . . are on the high road to extinction; and must ultimately be supplanted by those whom the pressure does so stimulate. . . . And here, indeed, it will be seen that premature death, under all its forms, and from all its causes, can not fail to work in the same direction. For as those prematurely carried off must, in the average of cases, be those in whom the power of self-preservation is the least, it unavoidably follows that those left behind to continue the race must be those in whom the power of self-preservation is the greatest, must be the select of their generation." Now, this is the doctrine of natural selection,