In similar fashion a primitive form of kidney is, as it were, sketched in, in the development of the higher animals, only to be erased at a later stage and replaced by a better form. The human child has a complete body covering of hair, which disappears soon after birth. In these and many more instances, one cannot avoid the impression that the organism has not been specially designed for what it finally comes to be. It cannot forget, and must needs repeat, or so it seems, some considerable part of the history of its race. Manifestly, then, all this evidence, gleaned from many different sources, points to a common origin of living things, and to the gradual evolution of the higher from the lower types. It may also be said that there is no scientific evidence against such a view. CHAPTER II UNICELLULAR AND MULTICELLULAR ANIMALS We must now turn to the main project of this book, which is to attempt to trace out the lines along which animal Evolution has proceeded, with special reference to that particular line which leads up to man. Indeed, we shall have to stick somewhat closely to this one main highway, and can but barely pause to glance along the numerous branch roads, interesting though the travelling there might be. It is perhaps necessary to say, at the outset, that the history of the Evolution of man cannot be written as a plain, matter-of-fact tale. Many portions of this history are tolerably well understood, but there are other periods, in some of which notable steps of progress were made, of which no record has ever been discovered. We must therefore expect occasionally to be reduced to speculation, and here and there to meet with controversy and with opposing theories.