He forgot also that survival does not in general depend on superiority in any one quality, but on a general average of superiority in all essential qualities, and therefore, since the fit survive and the unfit perish, there may be, if the struggle for existence is sufficiently severe, interbreeding notwithstanding, evolution in all the essential qualities, by the accumulation of inborn variations alone. As formerly he argued that the evolution by the accumulation of inborn variations alone of all the numerous qualities necessary for survival is, owing to their multiplicity, impossible; so now he argues that the evolution of any particular quality—e.g. fighting power—nay, even of any structure—e.g. horns—by the accumulation of inborn variations alone is impossible, owing to the multiplicity of the structures implicated in the evolution.
Leaving for a moment Mr. Spencer's theoretical objections, let us consider some facts of nature which are within the cognizance of every one. The children of the same parents usually differ appreciably when grown in their physical powers, as also do the individual members of a litter of puppies, or the individual chickens hatched from a nest of eggs. These variations must be due to inborn variations, not to variations acquired by the parents and transmitted to the offspring, for, at any rate as regards the puppies and chickens, the circumstances attending the genesis of each individual in the litter or brood are such as practically to preclude the possibility of any one differing from the others except through differences in inborn variations, since in each case all the spermatozoa and ova, and the organisms which arose from them, were circumstanced exactly alike as regards the parent organisms; in other words, if acquired variations are transmissible, each individual under the circumstances must have acquired the same variations, and therefore
