10 THE PROBLEMS OF EVOLUTION 



kell, the problems of evolution will be greatly mod- 

 ified, but with the knowledge at present available 

 I fail to see how it could overthrow completely the 

 intricate web of relationships now so convincingly 

 demonstrated in the field of evolution. For the 

 present everything points toward the adequacy 

 of a physico-chemical concept of the organism 

 as a basis for inquiry into this subject. 



Whatever life may be, the living being and its 

 functions are almost infinitely complex. Seem- 

 ingly organisms act by the exercise of intangible 

 forces resident within them, but it is increasingly 

 evident as time goes on that the foundation for 

 every action is tangible, and that only our igno- 

 rance of details conceals from us the whys of be- 

 havior. The skin of the frog darkens or becomes 

 pale, but it is not due to some mysterious power 

 of the animal. Darkening is brought about by 

 cold and dampness and is due to a specific stimu- 

 lant from certain parts of the pituitary gland 

 which causes expansion of the melanophores.^ The 

 digestive glands respond to the stimulus of food 

 under normal conditions, but secretin extracted 

 from the lining of the intestine will induce secre- 

 tion of pancreatic juice regardless of other condi- 

 tions.^ Far from being a completely discriminat- 

 ing unit, the organism is very largely a result of 

 complex interaction of substances governed by a 



^ Hogben, L. T., The Comparative Physiology oj Internal Secretion, 1927. 



