RELATION TO OTHER BIOLOGICAL CONCEPTS 9 



The separated fragment or the liberated germ-cell has in it 

 the possibility of becoming, in an appropriate environment, a 

 fully-developed organism. Is it possible to form any conception 

 verifiable or speculative of the manner in which the in- 

 heritance is thus condensed into a fragment or into a germ-cell ? 

 Is it possible to picture in any way how the potentialities come 

 to be realised in development ; how the obviously complex 

 grows out of the apparently simple ? To answer these and 

 similar questions is the business of the theory of development. 



The facts of inheritance are those which rise into prominence 

 when we compare the characters of an organism with those of 

 its parents and its offspring, or when we compare the characters 

 of one generation with those of its predecessors and successors. 

 This is a thoroughly concrete study, for the facts observed are 

 quite independent of any theory of the precise organic relation 

 which binds generation to generation (the theory of heredity), 

 and are also quite independent of any theory as to the way in 

 which the germ grows into the adult (the theory of development), 

 It is, in the main, an experimental and statistical study. 



Before the middle of the nineteenth century considerable 

 attention was given to what may be called the demonstration 

 of the general fact of inheritance that like tends to beget like. 

 This had, indeed, always been the general opinion of physicians 

 and naturalists, as well as of the laity, but it was a useful task 

 to collect documentary evidence showing that all the inborn 

 characteristics of an organism, whether physical or psychical, 

 normal or abnormal, important or trivial, were transmissible 

 to the offspring, if the possibility of having offspring had not 

 been excluded. This task of demonstrating inheritance was 

 well finished by Prosper Lucas, whose large treatise, published 

 in 1847, gave ample evidence for what we now take for granted, 

 that the present is the child of the past ; that our start in life is 

 no haphazard affair, but is rigorously determined by our paren- 

 tage and ancestry ; that all kinds of inborn characteristics may 



