The process of _induction_ is a logical system of forming conclusions _from the special to the general_, by which we advance from many individual experiences to a general law; _deduction_, on the other hand, draws a conclusion _from the general to the special_, from a general law of nature to an individual case. Thus the _Theory of Descent_ is, without doubt, a great _inductive law_, empirically based upon all the biological experience cited above; the pithecoid theory, on the other hand, which asserts that man has developed out of lower, and in the first place out of ape-like mammals, is a _deductive law_ inseparably connected with the general inductive law. The pedigree of the human race, the approximate outlines of which I gave in the last chapter but one, of course remains in detail (like all the pedigrees of animals and plants previously discussed) a more or less approximate general hypothesis. This however does not affect the application of the theory of descent to man. Here, as in all investigations on the derivation of organisms, one must clearly distinguish between the general _theory_ of descent and the special _hypotheses_ of descent. The general _theory_ of descent claims full and lasting value, because it is an inductive law, based upon all the whole series of biological phenomena and their inner causal connection. Every special _hypothesis_ of descent, on the other hand, has its special value determined by the existing condition of our biological knowledge, and by the extent of the objective empirical basis upon which we deductively establish this particular hypothesis. Hence, all the individual attempts to obtain a knowledge of the pedigree of any one group of organisms possesses but a temporary and conditional value, and any special hypothesis relating to it will become the more and more perfect the greater the advance we make in the comparative anatomy, ontogeny, and palæontology of the group in question. The more, however, we enter into genealogical details, and the further we trace the separate off-shoots and branches of the pedigree, the more uncertain and subjective becomes our special _hypothesis_ of descent on account of the incompleteness of our empirical basis. This however does no injury to the general _theory_ of descent, which remains as the indispensable foundation for really profound apprehension of biological phenomena. Accordingly, there can be no doubt that we can and must, with full assurance, regard the derivation of man—in the first place, from ape-like forms; farther back, from lower mammals, and thus continually farther back to lower stages of the vertebrata down to their lowest invertebrate roots, nay, even down to a simple plastid—as a general _theory_. On the other hand, the special tracing of the human pedigree, the closer definition of the animal forms known to us, which either actually belong to the ancestors of man, or at least stand in very close