Proofs of Evolution. 307 



wild state they would certainly be called different species, 

 and in some cases genera. If art accomplishes this result 

 by Artificial Selection, why not Nature by Natural Selec- 

 tion ? " 



The objectors say, " We cannot admit this evidence, for, 

 if your improved breeds are turned out again, they would 

 revert to original types." The Evolutionist replies : Hered- 

 ity is a plant of slow growth. It increases slowly and 

 holds firmly; time is the measure of its strength. If 

 pushed rapidly, it will hold lightly. This is a universal 

 principle ; what is longest in coining to maturity is strong- 

 est. He answers likewise : Domestic animals, if sent back 

 to the wild state, enter a new environment and must begin 

 anew a struggle for existence in competition with their 

 fellows of the woods. They are out of harmony with their 

 former artificial conditions, and a readjustment must take 

 place. Tame and wild animals are put on common ground. 

 They are forced into competition, and must needs fight or 

 die. The very principle of Evolution demands reversion in 

 such cases. 



There are, however, two interesting questions, not yet 

 fully answered ; although they do not affect at all the truth 

 or probability of the theory of Descent. First, what is the 

 cause of variation ? And, secondly, What is the cause of 

 the first step in usefulness ? Why should there be a tendency 

 to vary ? * Use can improve an organ, but how can it start 

 one ? And how does it start itself ? The answer to these 

 questions may perhaps be found in subsequent investigations 

 of the psychological phases of the life-problem. 



PROOFS FROM REVERSION. 



One of the most curious facts of Evolution is the tendency 

 to revert to ancestral forms. This at first seems to weaken 

 the theory of Descent, but in reality it gives it great sup- 

 port. It is all a question of environment. If that remains 

 the same, there will be little change in life-forms ; for this 

 reason the King-Crab and the Nautilus of to-day are quite 

 similar to their fossil parents. If former life-conditions 

 are restored, what is more natural than retrogression ? But 

 even here, paradoxical as it may seem, there is really 



* Since the delivery of this Essay, a writer in the " Popular Science Monthly" 

 for April, 1889, maintains with much force that the Tendency to Vary is due 

 largely to Psycho-Physiological influences. 



