606 THE POPULAR SCIENCE MONTHLY. 



was not victorious until, within the last decades, Charles Darwin led 

 upon the hard-fought logic-field an array of facts glittering in their 

 strength. Before a victory had been conquered by the Darwinistic 

 school, the specific forms of vegetal and animal life were held to be im- 

 mutable. While it was known that among the individuals of any one 

 species certain differences, justifying their being classed as distinct 

 varieties, might arise in the course of successive generations, all such 

 variations were held to be bounded by certain more or less narrow 

 limits of possibility. The facts adduced by the new school of biolo- 

 gists have led to different conclusions, culminating in the assertion 

 that all organic forms are changeable without limit — transmutable 

 without end — capable of a physical, intellectual, and moral elevation, 

 which knows no boundaries. 



According to the theory of evolution, the modifications of structure 

 and capability which organic forms are liable to undergo, in the course 

 of generations, may be traced back to three principal causes. The 

 first of these is the influence of physical forces, as, when the strength 

 of the muscles is enhanced by exercise, the mind invigorated by 

 thought, or, inversely, their function impaired by long-continued dis- 

 use. The second cause consists in the transmission of these results of 

 individual life to a line of descendants, the effects being compounded, 

 as they pass, with others of the same order. The third cause is to be 

 found in the competition of the forms so produced under circumstances 

 not equally well adapted to their capacities nor sufficient for their co- 

 existence, leading necessarily to the preservation of those races which 

 are best, and the extinction of those which are least, fitted to endure 

 adversity. To this last cause, constantly active in the organic world, 

 the term " natural selection " has been applied, to distinguish it from 

 the artificial selection of the stock-breeder and gardener. The changes 

 wrought in organic forms by the influence of inorganic forces are gen- 

 erally spoken of as variation. But this variation is in reality merely 

 an extension of the principle of competition. Organized beings are 

 brought face to face with the forces of Nature, with the earthquake, 

 the flood, the lightning, and the storm. Often they meet in mortal 

 conflict. The living form sinks to the earth before the power of the 

 thunder-bolt, or the thunder-bolt is conquered by the invention of ge- 

 nius. Death is but a victorious alliance of inorganic forces triumphing 

 over the organic form laid low on the battle-field ; life is but the vic- 

 tory of the organic forces over the inorganic hosts. But, do we not 

 also behold a competition taking place between, a struggle for exist- 

 ence and a natural selection occurring among, inorganic forms ? 

 Cast water upon fire ; either the water disappears as vapor or the fire 

 is extinguished. A mixture of salt and gravel is brought in contact 

 with water ; the salt is dissolved, the gravel remains unaltered. Heat 

 a mixture of salt and sal-ammoniac; the salt persists, while the sal- 

 ammoniac is vaporized. 



