However fitted this explanation may be to account for the gaps which so often present themselves in developmental series of animal structures, it is far from sufficient to account for the origin of man, at least on the assumption of evolution governed merely by mechanical principles. Neither man nor animals, in fact, could have come into being at all unless there had been an organic necessity, quite independent even of the general average effects of the relations of living bodies to their environments, insisted on by Mr. Spencer. That these agencies have been very influential in the evolution of organic nature is undoubtedly true. But their influence in this respect depends altogether on the organism on which they act being in a condition of unstable equilibrium. Mr. Spencer declares, when speaking of the condition of homogeneity being a condition of unstable equilibrium, that this instability is “consequent on the fact that the several parts of any homogeneous aggregation are necessarily exposed to different forces—forces that differ either in kind or amount.”[390] This may be true in relation to animal and vegetable forms, whose germs are supposed not to show the slightest trace of the future organism, although even as to these Mr. Spencer can say that “doubtless we are still in the dark respecting those mysterious properties which make the germ, when subject to fit influences, undergo the special changes beginning this series of transformations.”[391] But the unstable condition of the primeval homogeneous substance of nature could not be due to the cause assigned. For it requires the impossible case of certain forces, the action of which is supposed to result in the condition of instability, existing _outside_ of that substance which, as being identified with the Absolute, we must assume to be present throughout all space. The notion of an universally diffused homogeneous substance, acted on by external forces, appears to be contrary to reason; and the proper explanation of the original condition of instability would seem to be that it is natural to the primeval substance as the result of an innate energy, the internal force which constitutes its vitality. But this substance cannot have been merely “material.” There is just as little room for transition from the inorganic to the organic as from the animal to man; there is but one satisfactory starting-point—nature itself viewed as organic.