Dr. Downey follows Mr. Belloc in a curious disposition to score a point by declaring that this or that view of mine is twenty-five years old, quite out of date: “Mr. Wells has not kept pace with the rationalist movement,” and so forth. I do not understand this passion in Catholics for the latest mental wear; for my own part, if a thing is convincing to me, I do not care when it was first believed nor who has given it up. I thought that was the way with Catholics too. But Mr. Belloc assured the readers of the _Dublin Review_ that Natural Selection had not been believed in for twenty-five years; it was quite a discarded idea. If the intellectual smart set regards Natural Selection as out of date, that shows merely that the intellectual smart set has taken leave of common sense. The proposition is invincible that, given a species in which the individuals reproduce in greater or less abundance young with individual differences, and sooner or later die, and in which the individual young favour their individual parents, then in every generation the individuals less adapted to survive and reproduce are, as a rule, likely to die sooner and to bear fewer offspring than the individuals more adapted to these ends, and therefore that, conditions remaining constant, the average specimen of the species must become more and more perfectly adapted as time goes on to the conditions of its existence. And equally invincible is the proposition that a permanent change of conditions must involve a change in the average of a species to which no apparent limit is set short of perfect adaptation, and the parallel proposition that the average specimens of each of two sections of a species living under widely different conditions of survival, and separated from each other, must ultimately become widely different. I write of this not, as Dr. Downey says, with the “full-blooded confidence of the Sciolist,” but with the assurance of a normally sane man. If anyone can start from the premises I have just given and arrive at any other than the conclusion at which I have arrived, there is need for a psychological Einstein. It does not affect this question a jot that Mr. Bateson, always something of an _enfant terrible_ among biologists, celebrated the centenary of Charles Darwin, and the fiftieth anniversary of the publication of _The Origin of Species_, by writing in a collection of pious contributions to Darwin’s memory that “the time is not ripe for a discussion of the Origin of Species.” That was just Mr. Bateson’s fun. He himself has discussed it immensely. But he has discussed it from the point of view of _the cause of the individual difference_, and the theory of Natural Selection is not concerned with that. Natural Selection is merely a logical deduction from the facts of inheritance and individual difference. It explains neither, and no clear-headed biologist has ever thought that it did.