148 Report of the State Geologist. 



Natural Selection. — The principle of natural selection, dis- 

 covered by Darwin and Wallace, explains how individual varia- 

 tions accumulate and intensify among the descendants of one 

 and the same form until they produce at first varieties, and in 

 the end distinct species. This principle, so well known at pres- 

 ent that it is unnecessary to explain it in detail, c insists in this : 

 that the struggle for existence permits the survival and per- 

 petuation only of those forms capable of resisting changes in 

 their env^ironment which are often disadvantageous ; the varia 

 tions which are of utility, transmitted by heredity, will result in 

 the preponderance of the form which exhibits them, and will 

 become more pronounced with each succeeding generation. 

 When the diflFerentiation is pushed far enough, the new form can 

 no longer cross with that from which it sprang, and a species is 

 established ; the primitive form may either entirely disappear, 

 or may persist without modification, or may evolve in several 

 different directions. . 



Palaeontology can bring no direct argument in support of the 

 principle of selection. But this principle is the foundation of 

 the entire transformist doctrine, the various propositions of 

 wjiich constantly receive from Palaeontology demonstrative 

 verifications. 



Intermediate forms. — We must pause here to consider an 

 objection which is made to the hypothesis of the evolution of 

 forms. It has been observed that if species are derived grad- 

 ually, one from another, one ought always to find intermediate 

 types, and the two extremes must- embrace a series of forms 

 strictly continuous To this it may be replied that the very 

 principle of natural selection supposes that the intermediate 

 forms could not be of very long existence, since they lie, so 

 to say, between two fires. It is then a natural consequence that 

 in existing nature there should not be found any transition forms 

 between different species, unless in the case of a new form whose 

 evolution is not yet completed. This occurs in fact in cases 

 which the progress of observations has shown to be more and 

 more frequent. 



♦Wallace. Darivlnism, 1891. Welsmann, Essay on Heredity and Natural Selection. Fr. trans., 

 1892. 



