200 Inheritance of Acquired Characters 



mentioned or from some other accidental cause, man 

 on the contrary modifies his environment directly and 

 continuously by the products of civilization. And this 

 unceasing modification of the environment results in the 

 unceasing evolution of the man. 



It is thus for example with cerebral development. 

 Civilization itself and the continual progress of science 

 and arts make steadily increasing demands upon the 

 brain. And this mental exercise, steadily increasing from 

 generation to generation, contributes always to the 

 development of the brain. What wonder then, if the 

 cranial capacity of man has become markedly increased 

 even during the three last centuries, as is stated by the 

 anthropologists ? 



Another cause whereby one portion of a given species 

 can remain unaltered while the remaining portion 

 becomes transformed, is found, when once the inherit- 

 ability of acquired characters is admitted, in the sudden 

 apparition of certain instincts. "Also in the domain of 

 biology," writes Emery, "and very especially in that 

 domain, many characters of organisms seem to me to 

 permit of explanation only by sudden formation. This 

 is especially true of habits and instincts. How could 

 the first Velleius dilatatus arrive gradually at its para- 

 sitic life in the nest of the hornet? The first cuckoo 

 certainly commenced suddenly to deposit its eggs in the 

 nest of a strange bird." 154 



The first sudden appearing of a new instinct can be 

 compared to a happy thought. It is a definite association 

 of ideas which is formed for the first time. But when 

 it has once been formed, it is easily possible and indeed 



1B4 Emery: Gedanken zur Deszendenz- und Vererbungstheorie. 

 Biol., Centralbl., July 15, 1893. P. 416. 



