The great majority of these express what may be called popular Darwinism [“Darwinismus vulgaris”], theoretically worthless, but practically possessed of great powers of attraction and propagandism. It expresses in the main a conviction, usually left unexplained, that everything “happens naturally,” that man is really descended from monkeys, and that life has “evolved from lower stages” of itself, that dualism is wrong, and that monism is the truth. It is exactly the standpoint of the popular naturalism we have already described, which here mingles unsuspectingly and without scruple Lamarckian and other principles with the Darwinian, which is enthusiastic on the one hand over the “purely mechanical” interpretation of nature, and on the other drags in directly psychical motives, unconscious consciousness, impulses, spontaneous self-differentiation of organisms, which nevertheless adheres to “monism” and possibly even professes to share Goethe’s conception of nature! Above this stratum we come to that of the real experts, the only one which concerns us in the least. Here too we find an ever-growing distance between divergent views, the most manifold differences amounting sometimes to mutual exclusion. These differences occur even with reference to the fundamental doctrine generally adhered to, the doctrine of descent. To one party it is a proved fact, to another a probable, scientific working hypothesis, to a third a “rescuing plank.” One party is always finding fresh corroborations, another new difficulties. And within the same group we find the contrasts of believers in monophyletic and believers in polyphyletic evolution, the mechanists and the half-confessed or thoroughgoing vitalists, the preformationists and the believers in epigenesis. Opinions differ even more widely in regard to the _rôle_ of the “struggle for existence” in the production of species. On the one hand we have the Darwinism of Darwin freed from inconsequent additions and formulated as orthodox “neo-Darwinism”; on the other hand we have heterodox Lamarckism. The “all-sufficiency” of natural selection is proclaimed by some, its impotence by others. Indefinite variation is opposed by orthogenesis, fluctuating variation by saltatory mutation (Halmatogenesis in “Greek”), passive adaptation by the spontaneous activity and self-regulation of the living organism. The struggle for existence is variously regarded as the chief factor, or as a co-operating factor, or as an indifferent, or even an inimical factor in the origination of new species.