WHAT IS THE ORIGIN OF SPECIES? 1 97 



The essential idea set forth by Cope may be found in the 

 following quotation from the chapter "On the Origin of 

 Genera" : 



" There are, it appears to us, two laws of means and modes 

 of development [evolution]: I. The law of acceleration and 

 retardation. II. The law of natural selection. It is my pur- 

 pose to show that these propositions are distinct, and not one 

 a part of the other: in brief, that, while natural selection 

 operates by the * preservation of the fittest,' retardation and 

 acceleration act without any reference to ' fitness ' at all ; that 

 instead of being controlled by fitness, it is the controller 

 of fitness. Perhaps all the characteristics supposed to mark 

 generalized groups from genera up (excepting, perhaps, fami- 

 lies) have been evolved under the first mode, combined with 

 some intervention of the second, and that specific characters 

 or species have been evolved by a combination of a lesser 

 degree of the first with a greater degree of the second mode." 



Growth-force or Bathmism. The defenders of this view are 

 called by Wallace, in criticising them, the American school 

 of Evolutionists.* There is assumed to be a special develop- 

 mental force, called growth-force or " bathmism," which is 

 exhibited in variation itself, and becomes effective, as phylo- 

 gerietic evolution, through retardation and acceleration, in the 

 same way as the force which is expressed in natural selection 

 operates through the death of the unfit and "the survival of 

 the fittest toward the evolution of species. 



The Origin of Species Still an Open Question. Many other 

 theories have been advanced to explain the origin of species: 

 the examples above cited are sufficient to explain the nature 

 of the problem ; but it is aside from the purpose of this 

 treatise to go into detail in the discussion of theories. 



It will be observed from the statements already made 

 that the two great factors in evolution and the origin of spe- 

 cies are species and mutations. Species with the repetition 

 of characters and the adjustment to environment are facts 

 which every naturalist is more deeply aware of the fuller his 

 knowledge of organisms becomes. Mutation, or the acquire- 



* Wallace, "Darwinism," p. 420. This American school is in other places 

 called the Neolamarckian school. 



