Many cases have been adduced of striking likenesses between different animals, not due to inheritance; but this should be the less surprising, in that the very same individual presents us with likenesses between different parts of its body (_e.g._, between the several joints of the backbone), which are certainly not so explicable. This, however, leads to a rather large subject, which will be spoken of in the eighth chapter of the present work. Here it will be enough to affirm (leaving the proof of the assertion till later) that parts are often homologous which have no direct genetic relationship,--a fact which harmonizes well with the other facts here given, but which "Natural Selection," pure and simple, seems unable to explain. But surely the independent appearance of similar organic forms is what we might expect, _a priori_, from the independent appearance of similar inorganic ones. As Mr. G. H. Lewes well observes,[74] "We do not suppose the carbonates and phosphates found in various parts of the globe--we do not suppose that the families of alkaloids and salts have any nearer kinship than that which consists in the similarity of their elements, and the conditions of their combination. Hence, in organisms, as in salts, morphological identity may be due to a community of causal connexion, rather than community of descent. "Mr. Darwin justly holds it to be incredible that individuals identically the same should have been produced through Natural Selection from parents _specifically distinct_, but he will not deny that identical forms may issue from parents _genetically distinct_, when these parent forms and {95} the conditions of production are identical. To deny this would be to deny the law of causation." Professor Huxley has, however, suggested[75] that such mineral identity may be explained by applying also to minerals a law of descent; that is, by considering such similar forms as the descendants of atoms which inhabited one special part of the primitive nebular cosmos, each considerable space of which may be supposed to have been under the influence of somewhat different conditions. Surely, however, there can be no real parity between the relationship of existing minerals to nebular atoms, and the relationship of existing animals and plants to the earliest organisms. In the first place, the latter have produced others by generative multiplication, which mineral atoms never did. In the second, existing animals and plants spring from the living tissues of preceding animals and plants, while existing minerals spring from the chemical affinity of separate elements. Carbonate of soda is not formed, by a process of reproduction, from other carbonate of soda, but directly by the suitable juxtaposition of carbon, oxygen, and sodium.