432 EVOLUTION AND GENETICS 



implied that they are the effects of environment impressed upon 

 organisms. This is true of very few characters. Mutilations are, 

 of course, produced in an organism in spite of its inherent qualities, 

 and when the woman of today has her hair curled, no inherent 

 quahty of the hair determines the wave, as in the kinky hair of 

 the negro. No one would seriously consider such characters in 

 connection with evolution, although it has been done in the past. 

 The vast majority of acquired characters or modifications are of a 

 very different nature. The formation of calluses, tanning of the 

 skin, muscular development and other so-called modifications are 

 due to individual response to conditions in the external environ- 

 ment, it is true, but can they be produced without the action of a 

 definite heritage? 



A simple illustration will show that both heritage and environ- 

 mental stimulus are as essential in their production as in that 

 of other characters. The ability of the body to deposit pigment is 

 an inherited character. Some people tan readily when exposed to 

 strong sunlight, others burn without tanning and others freckle, 

 but in the case of alienism the heritage is deficient. Albinos can 

 deposit no pigment, therefore no amount of sunlight produces 

 this so-called modification in their bodies. It seems that a char- 

 acter which arises from the response of the heritage to a stimulus 

 from the internal environment may be interpreted as solely a 

 product of the heritage in a broad sense, since the environmental 

 stimulus in this case is another product of the heritage, but in 

 many cases we find that the internal environment merely serves 

 to make available in the proper form certain factors from the 

 external environment. Proper development of the thyroid gland, 

 for example, cannot be attained unless the food contains a sufficient 

 amount of iodine. Even the internal environment is therefore 

 tempered by external environmental conditions. None of the 

 characters which are of interest to us in the study of evolution 

 can be a product entirely of either heritage or environment alone. 

 The true distinction between the Darwinian and Lamarckian point 

 of view is not the source of the character, hut the source of the stimulus 

 which governs its appearance. 



The Role of the Gene. A distinction arising from genetics 

 should be clearly understood at this point. The function of the 

 genes as determiners of hereditary characters has been so well 

 established that in speaking of the heritage we must think of the 



