Such was the theory of Lamarck, and it is sound and plausible in all respects save one, namely, the unwarranted assumption that acquired adaptations are inheritable, since these, to quote the words of the Harvard zoölogist, G. H. Parker, “are as a matter of fact just the class of changes in favor of the inheritance of which there is the least evidence.” (“Biology and Social Problems,” 1914, p. 103.) The next contribution to the philosophy of transformism was made by Charles Darwin, when, in the year 1859, he published his celebrated “Origin of Species.” In this work, the English naturalist bases the evolution of organic species upon the assumed spontaneous tendency of organisms to vary minutely from their normal type in every possible direction. This spontaneous variability gives rise to slight variations, some of which are advantageous, others disadvantageous to the organism. The enormous fecundity of organisms multiplies them in excess of the available food supply, and more, accordingly, are born than can possibly survive. In the ensuing competition or struggle for existence, individuals favorably modified survive and propagate their kind, those unfavorably modified perish without progeny. This process of elimination Darwin termed natural selection. Only individuals favored by it were privileged to propagate their kind, and thus it happened that these minute variations of a useful character were seized upon and perpetuated “by the strong principle of _inheritance_.” In this way, these slight but useful modifications would tend gradually to accumulate from generation to generation in the direction favored by “natural selection,” until, by the ensuing summation of innumerable minor differences verging in the same direction, a major difference would be produced. The end-result would be a progressive _divergence_ of posterity from the common ancestral type, whence they originally sprang, ending in a multiplicity of new forms or species, all differing to a greater or lesser extent from the primitive type. The contrary hypothesis of a possible _convergence_ of two originally diverse types towards eventual similarity Darwin rejected as an extremely improbable explanation of the observed resemblance of organic forms, which, not without reason, he thought it more credible to ascribe to their assumed divergence from a common ancestral type.