108 EVOLUTION THE RESULT OF CHEMICAL FORCES. 



If however, according to the theory of evolution, this most 

 important of all the advances in organic nature was worked out 

 in any way by the hereditary transmission of slight advantageous 

 changes, the great question comes back to ITS : what was there in 

 nature, or in the environment, or in the struggle for existence, to 

 induce or start any tendency to any such change ? The old mar- 

 supials were prolific enough, were apparently successful with 

 their mites of embryos, were good feeders, well balanced in 

 their orders, and filled satisfactorily every sphere in life. Al- 

 though a little dull and lacking in brain capacity, yet they were 

 physically a powerful race, and held their sway until the 

 improved order came fully branched and developed to take their 

 places. There was not only no necessity for the change, but no 

 such ad vantage in its first stages as would cause them to be selected 

 and perpetuated. Yet the great transformation came, according 

 to the testimony of geology, suddenly and unheralded, just as 

 many other changes in ancient life-histories have come. The 

 great geologist and evolutionist, LeConte, has been obliged to 

 specify this as one of his " critical periods," when life-forms 

 were subject to sudden and most unaccountable variations. 

 Writing of the era of the mammals, he says: "There is at cer- 

 tain geological horizons, a rapid and most extraordinary change 

 in life-systems. This it seems impossible to explain on the 

 theory of evolution, unless we admit periods of rapid evolution." 



It seems to me very much as if these grand and radical 

 advances came because they could not help it, because in the 

 great plan of organic life the times had come when it was neces- 

 sary they should rapidly develop. Just as in the life of the 

 amphibian frog, the time comes when it must lay aside the 

 habits and organs adapted to a water life, and take on the full- 

 boned members, the lungs, and the sense organs necessary to a 

 life on land. The hairy caterpillar, with a mandibulate mouth, 

 with cutters and jaws and stomach for eating and digesting leaves 

 or other vegetable food, after storing up a quantity of living 

 matter, goes to sleep in its chrysalid case. In this condition all 

 the parts of the caterpillar, the mouth, the members, the organs, 

 the muscles and tissues and nerves, entirely disappear, and there 



