CHAPTER IX 



Environment as the cause of acquired characters but not of inborn variations- 

 Discussion of so-called inherited diseases Cases claimed as proving the 

 transmission of acquired characters Acquired immunity and inborn im- 

 munity Brown -Sequard's experiments The inheritance of instincts 

 Social bees and ants Effect of illness upon growth Favourable conditions 

 cause degeneration Stringent selection causes improvement The case for 

 the transmission of acquired characters Environment causes selection 

 Lamarckian explanation of immunity Natural selection of inborn varia- 

 tions is a question of adaptation to the environment Lamarckian explana- 

 tion of the production of physical characters Inborn variations arise in the 

 germplasm Conclusions. 



THE action of the environment upon an organism has been 

 claimed by some writers as the cause of variation in its 

 offspring. In considering this question it is necessary to 

 have a very clear idea of what it means. We have seen 

 that the environment may produce very great modifications 

 in the individual. These modifications are acquired char- 

 acters, and appear in the individual at different periods of 

 its life, in response to stimuli from without. They are not 

 inborn characters, and unless the necessary stimulus is 

 applied, they will not appear. Variations, however, are 

 inborn, that is, they are present in the germ cells, and 

 appear independently of any stimulus. In other words, 

 the inborn characters of the individual are not dependent 

 on the environment, unless indeed the environment is such 

 as to kill the organism. All the environment can do is to 

 modify the inborn characters. Some stimuli may add to the 

 inborn characters. Use will develop the muscles and other 

 tissues in man and other mammals. Long exposure to a 

 tropical sun will bronze a European, and this may be carried 

 to such a length that the skin may not lose its pigmentation 

 even after many years subsequently spent in a temperate 



