infer from them with mathematical certainty that it must have occurred. It is a matter of common knowledge and experience (1) that in both the animal and vegetable kingdoms every individual differs somewhat from every other individual, but that (2) while the offspring is never an exact copy of the parent, there is yet a tendency for the peculiarities of the parent to reappear in the offspring in a greater or lesser degree. Whence it is clear, if some individuals of a species possess a peculiarity, such as a superior keenness of sight, or of hearing, or of scent, or a power of muscle, or a capacity of resisting heat, or cold, or hunger, or thirst, or disease, &c., in a greater degree than that possessed by the other members of the species, under conditions which render this peculiarity of importance in the struggle for existence, that the individuals which possess the peculiarity in the greater degree will be at an advantage, and will, on the whole, survive in greater numbers, and, consequently, other things equal, have a more numerous offspring than those which possess the peculiarity in the lesser degree. And further, since the offspring, while inheriting their parents' peculiarities, tend, to vary somewhat from them, there will, in the next generation, probably be some who have the peculiarity in a greater degree than their parents, and others who have it in a lesser degree, when, if the conditions remain the same, there will be such a new survival of the fit, and such a fresh elimination of the unfit, as will leave the survivors in the third generation with the peculiarity developed, in however slight a degree, more than it was developed in their grandparents; and it follows that this process, repeating itself through innumerable generations, and during long epochs of time, will at length develop the peculiarity to a point beyond which any further increase is no longer useful, or to a point beyond which it is so little
