164 HEREDITY AND ENVIRONMENT 



bell, that chromosomes are not the causes of 

 anything, but that they are the "results of 

 dynamic processes," "the expression rather 

 than the cause of cell activities." This objec- 

 tion seems to confuse the idea of natural cause 

 with that of final cause. Science knows noth- 

 ing of the latter; any natural cause is only a 

 link in the chain of cause and effect, it is itself 

 the result of antecedent causes and the cause 

 of subsequent results. Undoubtedly the 

 chromosomes are the result of antecedent pro- 

 cesses, and yet they may also be the causes of 

 subsequent processes. No thoughtful person 

 has ever maintained that chromosomes or any 

 other things in nature are autonomous, abso- 

 lute, uncaused causes. 



There are certain general and a priori rea- 

 sons for assuming that the chromosomes are 

 important factors in heredity and differentia- 

 tion: (1) they come in approximately equal 

 numbers from the father and the mother, (2) 

 one-half of each of the maternal and paternal 

 chromosomes is distributed to each cell of the 

 developing organism, (3) in the formation of 



