302 O. F. COOK 



dividuals, but a fabric of interwoven lines of descent, and it is 

 only in such associations that evolutionary progress goes for- 

 ward, or that the vitality of organisms can be permanently 

 maintained. 



The standpoint from which these biological relations can be 

 perceived was indicated as far back as 1895, but was first for- 

 mally presented in 1901.^ It differs fundamentally from earlier 

 structures in the same field of thought in its conception of the 

 nature of evolutionary motion. Two alternatives had thus far 

 monopolized the interest of the scientific world, and both had 

 proved to be inadequate to accommodate the facts of organic 

 existence, or to conduct us toward more detailed explanations 

 of them. 



The progressive development of organisms had been con- 

 ceived as due (i) to environmental causes, and (2) to determi- 

 nate internal forces or " hereditary mechanisms." The kinetic 

 theory was the result of contact with facts which showed that 

 both these suppositions were wrong. The true actuating causes 

 of evolution do not lie in the environment. Neither is the for- 

 ward progress or vital motion of species determinate, or re- 

 stricted to a particular direction ; it has great freedom of choice 

 of environmental opportunities.^ 



The kinetic interpretation accommodates and admits natural 

 and consistent relations between numerous other facts which 

 had appeared to conflict with each other or with the doctrines 

 which had undertaken to explain them. The normal condition 

 of evolutionary progress is found in symbasis, that is, in the 

 traveling together of the members of the specific group. New 

 variations among the individuals of such groups are prepotent 

 and can be preserved, whether useful or not, without being seg- 

 regated. The environment does not cause the evolutionary 

 variations, but it can induce adaptations by restricting the pro- 

 gressive development of the species to particular directions or 

 characters. Selection is thus a negative factor, instead of a 

 positive or actuating agency of evolutionar}- motion. 



'A Kinetic Theory of Evolutioti, Science, N. S., 13 : 969. 

 ^ Evolutionary Inferences from the Diplopoda, Proc. Entomological Society 

 of Washington, 5 : 14, March, 1902. 



