The actual attack and testing of the Theory of Natural Selection have yielded negative results. The statement of the theory may have been made finer and exacter, that is all. And yet the conditions of its survival have been very exacting. If the theory is to stand, the whole of plant and animal life in time and space must be arranged in a certain order. It must be possible to replace classification by a genealogical tree. Every form must fall without difficulty into its proper place in that tree. If it is true that birds are descended from reptiles or men from apes, then there must be no birds before the reptiles appear, and no men before apes. The geological record is manifestly a mere fragmentary history, still for the most part unread, but, however fragmentary it is, it must be consistent. One human skull in the coal measures blows the whole theory to atoms. The passage from form to form must be explicable by intermediate types capable of maintaining themselves; there may be gaps in the record, but there must be no miraculous leaps in the story. If an animal living in the air is to be considered as a lineal descendant of some animal living in the water, then the structure of the former bit by bit and step by step must be shown to be adapted, modified, changed about from that of the latter; it must have ears for water-hearing modified for air-hearing, and its heart and breathing arrangements must be shown to be similarly changed over, and so on for all its structure. All these requirements will follow naturally from the necessities of a process of Natural Selection. They follow logically upon no other hypothesis. They are not demanded, for example, by the idea of a Creator continually interfering with and rectifying some stately, unaccountable process of “Evolution,” which seems to be Mr. Belloc’s idea--so far as he ventures to display any idea of his own--in the matter. Such things as vestigial structures and a number of odd clumsinesses in living things--many still very imperfect adaptations to an erect position, for example--become grotesque in relation to such a view. A Creator who put needless or inconvenient fish structures into the anatomy of a land animal and made the whole fauna and flora of the land a patch-up of aquatic forms of life must be not so much a Divinity as a Pedant. But it is the burthen of the whole beautiful science of comparative anatomy that the structure of animals and plants, and their succession in time, fall exactly into the conditions defined by the Theory of Natural Selection. In the most lovely and intricate detail, in a vast multitude of examples, in plants and in animals alike, this theme of the adaptation of pre-existing structure is worked out.