Let me summarize these Implications.
(1) First, Change must be continual and types must be always in a state of flux. Stability of Type and Natural Selection form a contradiction in terms. You can have one or the other—but you cannot have both.
(2) Second, Natural Selection inevitably implies that, on searching the records of Evolution, we shall find only gradual change, proceeding continually, so that the ascending organisms follow, as it were, regular inclined planes showing no steps. The whole of Evolution should, under Natural Selection, prove to be of this kind. Thus you would have, say, tigers as they are now, gradually developing out of some tiger-like ancestor in the past by a regular and uninterrupted process, never achieving a fixed type but perpetually changing as time went on; and that perpetual change would be still going on to-day. The world about us would not show (as it does) a vast number of strongly separate types but a confused jumble of forms all melting one into the other.
(3) Third, Natural Selection presupposes Evolution through the killing off of individuals lacking certain advantages, how then do other types continue still to be with us in spite of lacking these advantages?
(4) Fourth, Natural Selection must stand or fall of itself. If you try to prop it up with Will or Design, inherent in the organism, or acting in any other fashion, you destroy its whole thesis. If you say, for instance, “the country becoming dryer, animals which adapted themselves to the new conditions survived, and those that could not adapt themselves died out,” that is no example of Natural Selection as an agent of Evolution. For when you say “Animals which adapted themselves to the new conditions,” you are presupposing some inherent power in the animal to adapt itself: you are presupposing a form of Will and Design, and thereby denying the purely mechanical action, the unintelligent “sieve,” of Natural Selection as an agent.
(5) Fifth, Natural Selection presupposes, quite gratuitously, that new survival values will be perpetually and progressively appearing. That sheep woollier than the average of a flock have survival value as the winters get colder is obvious: too obvious to need stating. But why should the next generation, under mere chance, produce a number of new still woollier variations, and the one after that yet another even woollier set; and so on indefinitely?
(6) Sixth, Natural Selection presupposes that in every stage of the slow process of development by infinitesimal differences, each successive difference is more advantageous than the last and has a special survival value.
A bird with fully formed wings has a survival value through being able to fly away from land enemies. But if it evolved from a reptile by Natural Selection, then each stage between the useful Reptilian fore-leg and the useful wing must have had a special advantage over the stage immediately preceding it. There must have been an advantage in the fore-leg getting stumpy, then in its getting stumpier, then its getting so stumpy that the beast couldn’t use it at all. And this must be true of every change in all the millions of tiny evolutionary changes proceeding through æons of time. All the way along, from the first signs of something which later on will be an advantage to the mature type, through myriads of generations, from the first origins when the organ was as yet rudimentary to the last when it was perfected, every step must have had a survival value over the last. And this must apply not only to broad cases, such as the reptile’s fore-leg turning into the bird’s wing, but to every one of innumerable organs and to every part of each organ. Otherwise the theory breaks down.
The implications then of Natural Selection as the blind agent of development, “give one furiously to think.” Merely stated roughly as I have done here, they shake the ordinary man’s confidence in it. But when we come to ordered proofs against it, we shall find those proofs conclusive.
To these I now turn.