THE EFFECTS OF ENVIRONMENT ON ANIMALS^ 



PKOFESSOR A. S. PEARSE 



As Henderson^ has pointed out, the environment on the 

 surface of the earth is suited to, and largely responsible 

 for, the existence of living organisms. After an organism 

 comes into existence, it strives to live in harmony with 

 its immediate environment. An organism is a "system 

 of activities'" which devotes its energies primarily to 

 three functions: (1) capturing energy for and releasing 

 energy from its own system, (2) protecting its system 

 from injury, and (3) producing other systems of activi- 

 ties similar to itself. If possible an organism reacts with 

 its environment in such a way that its system continues 

 to exist and carry on its three primary functions. It is 

 limited in its responses to a particular behavior pattern, 

 inherited from the system from which it came, but in 

 general it reacts in such a way toward its environment 

 that it selects by trial the optimum conditions for its own 

 existence. In other words, an organism generally re- 

 sponds in an adaptive way and selects the best environ- 

 ment that it can. If the behavior patterns of certain sys- 

 tems, similar or dissimilar, are well suited to a particular 

 environment, such systems often are "successful." They 

 may take possession of the environment, perhaps exter- 

 minating other systems, and, thus demonstrating their 

 "fitness," constitute what ecologists call a climax forma- 

 tion. Every organism in such a group must remain a sys- 

 tem of activities and must make continual physiological 

 adjustments to keep in harmony with the environment, or 

 it can not continue to exist. Each organism assumes a 



1 An address before the Geographical Society, IJniversity of Wisconsin, 

 January 11, 1922. 



2 " The Order of Nature," Cambridge, 1917. 



3 This definition is not intended to exclude the possibility that an organism 



