THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 301 



If this general principle is a sound one, it follows: 



First, that working hypotheses which treat of the internal and external 

 factors as separable phenomena are unsound. 



Second, that all methods of investigation or experiment which proceed upon 

 such hypotheses are unsound. 



Third, that granting the general truth of the law of the inseparable factors 

 investigation and experiment will be directed upon the following specific inquiries: 



(a) Under what conditions are readjustments initiated? 



(6) Are readjustments initiated (1) by one factor or (2) by more than one, 

 or (3) by a combination of the factors, or (4) under certain conditions by one* 

 factor and under other conditions by another, and thus possibly by each of tin- 

 factors in turn? 



One of the best illustrations of the difficulty of determining the point of 

 initiation is exhibited by the time-honored problem of the inheritance of acquired 

 characters, or the transmission of the effects of use and disuse. In such instances 

 we observe the following parallelism as regards many characters : 





Ontogeny. 



Heredity. 



Ontogenic development. Ontogenic development. 



Phylogenic degeneration. Phylogenic degeneration. 



Fluctuations arising from body cells. Fluctuations arising from germ cells. 



Neomorphs originating in body cells. Neomorphs originating in germ cells. 



The question whether this kind of ontogenic initiation or somatic genesis of 

 character has any bearing in heredity is of course the crucial Lamarckian question. 



So far as the law of the inseparable factors is concerned we must constantly 

 remind ourselves that this kind of ontogenesis is a constant phenomenon in a state 

 of nature, not an exceptional one, that any animal forced into new or unusual 

 environment under the stress of which new ontogenic characters are appearing will 

 produce these characters generation after generation and that such characters will be 



regarded by the systematist as of taxonomic value. Ontogeny is in this sense 

 initiative exactly as environment is initiative. 



2. Initiation in Environment. 



The initial influence of environment in the modification of characters is part 

 of the ancient doctrine of Buff on. It has been beautifully illustrated recently 

 in the interesting experiments of Beebe 1 conducted in the New York Zoological 

 Park, in which the eggs and young of the same mother bird were subjected to 

 two extremes of environment, resulting in the ontogeny of two types of plumage. 

 Here the formula of the inseparable factors is clearly the following: 



HXO'XE'XS. 



1 Beebe, C. William, Geographical Variation in Birds with Espe 

 Humidity. Zoologka, N. Y. Zool. Soc, vol. I, No. 1, Sept. 25, 1907. 



