More important than a knowledge of what, according to the theory of chances, fluctuating variations will do, will be information that would tell us what changes will take place in each individual. In this field we may hope to obtain data no less quantitative than those of chance variations, but of a different kind. A study of some of the results of discontinuous variation will show my meaning more clearly. Discontinuous Variation Galton, in his book on “Natural Inheritance,” points out that “the theory of natural selection might dispense with a restriction for which it is difficult to see either the need or the justification, namely, that the course of evolution always proceeds by steps that are severally minute and that become effective only through accumulation.” An apparent reason, it is suggested, for this common belief “is founded on the fact that whenever search is made for intermediate forms between widely divergent varieties, whether they are of plants or of animals, of weapons or utensils, of customs, religion, or language, or of any other product of evolution, a long and orderly series can usually be made out, each member of which differs in an almost imperceptible degree from the adjacent specimens. But it does not at all follow because these intermediate forms have been found to exist, that they were the very stages that were passed through in the course of evolution. Counter evidence exists in abundance, not only of the appearance of considerable sports, but of their remarkable stability in hereditary transmission.” Comparing such an apparently continuous series with machines, Galton concludes, “If, however, all the variations of any machine that had ever been invented were selected and arranged in a museum, each would differ so little from its neighbors as to suggest the fallacious inference that the successive inventions of that machine had progressed by means of a very large number of hardly discernible steps.”