Of these theories the first and last only need detain us; and since the theory of evolution is the one more generally accepted by scientific men, and is making rapid progress among the masses, I think it proper to state the basis of this theory more in detail. The absurdities which theologians have associated with the first named hypothesis of the origin of man and the universe is largely responsible for the existence of the theory of evolution. Finding so much that was contrary to well known facts, not so much in the theory itself, as in the explanations of it by its advocates, induced men of intelligence to look for some other explanation of the genesis of things. It was doubtless observed that many remarkable resemblances exist between man and the inferior animals. In embryonic development, in physical structure, in material composition and the functions of organs, man and the superior animals are strikingly alike. The skeleton of man when examined minutely and compared with the skeletons of the higher order of animals, seems only a modification of them, and in some instances the modifications appear extremely slight. This resemblance also exists among the inferior animals, and it was this, doubtless, which gave birth to the idea of a common origin for all existing species. Side by side with the above mentioned facts are others that sustain, it is claimed, the idea of common origin; and suggest an explanation of how the varieties of animal and vegetable forms were brought into existence. The great law of nature is for like to beget like; the tendency of offspring is always to reproduce the parent forms, as every seed produces its kind; that is the general law of nature, and to it a special name is given--it is called _atavism_. But notwithstanding this general law, there is a modification of it, a tendency to variation, slight in some cases and more marked in others. This is a matter of common observation. The male does not follow the precise type of the male parent, nor does the female always inherit the precise characteristics of the mother. "There are all sorts of intermixtures and intermediate conditions between the two, where complexion, or beauty, or fifty other different peculiarities belonging to either side of the house, are reproduced in other members of the same family." This kind of variation in cases where offspring are produced by sexual propagation is attributed to the fact that the thing propagated proceeds from two organisms of different sexes and temperaments. Breeders of our domestic animals take advantage of this tendency to variation, to produce such varieties as are most desirable; and, indeed, for that matter, to obtain new varieties by crossing breeds. Sometimes this tendency to variation acts in the most remarkable and unaccountable manner, and because naturalists can assign no reason for it. they have called it "spontaneous variation." That it may be