THEORIES OF EVOLUTION 163 



breed together. Slight variations before they be-- 

 come fixed are very unstable, and they would very 

 likely disappear if the breeding were general with 

 species exhibiting counter variations. Isolation of 

 species, by geographical barriers or other natural cir- 

 cumstances, would lead to interbreeding and favor 

 the perpetuation and improvement of small varia- 

 tions. After the variations are started and lifted to 

 a plane where natural selection can take hold, then 

 the latter agent would become operative. Natural 

 selection originates nothing but guides the course of 

 evolution after variations are sufficiently developed 

 to make a difference in the struggle for existence. 



Before closing this chapter a word regarding the 

 present status of the doctrine of organic evolution 

 will be in order. With so many discussions in 

 scientific circles regarding aspects of evolution there 

 is little wonder that the general public should be 

 confused, and that reports are often circulated that 

 there is a tendency on the part of the scientific world 

 to recede from the doctrine or even, to surrender it. 

 This vagueness regarding the present status of the 

 theory of organic evolution arises chiefly from not 

 understanding the nature of the points at issue. 

 Never before was the doctrine of organic evolution so 



