174 THE FIRST PRINCIPLES OF HEREDITY 



being supplied by the forces of the outside world, which 

 are worked up by the growing body. No sensible person 

 would expect to rear an oak from an acorn without putting 

 it into the proper surroundings the right kind of soil, etc. 

 But whilst positing so much a fact which every scientist 

 admits, nay, insists upon, as an essential physiological 

 requirement of the growing organism we are not com- 

 mitted to any further implications involved. For in- 

 stance, it does not follow as a deduction from the above 

 fact that, as environmental influences affect the individual 

 to a certain extent, such effects react, as a matter of course, 

 on the subsequent offspring. This is, indeed, the assumption 

 which the Lamarckian makes in order to explain the 

 evolution of species by the accumulated results of acquired 

 characters. We have already given in full the arguments 

 against the Lamarckian theory, showing that so far our 

 knowledge does not warrant any such assumption. En- 

 vironment plays an important role in the evolution of 

 species, but, according to the now generally accepted view 

 of most scientists, not in the manner represented by 

 Lamarck i.e., by the directly inherited effect of changed 

 surroundings. On the contrary, according to Darwin's 

 theory of Natural Selection, the environment does not alter 

 the characteristics of the individual directly, but only 

 selects such individuals as possess certain characters most 

 suitable to that environment, the remaining members of 

 the species being weeded out in the struggle for existence. 

 By thus constantly eliminating those unfit for the prevailing 

 conditions, the constant change of environment leads to a 

 progressive change of the species, thus bringing about its 

 gradual transformation. We see that the role which 

 environment plays in the evolution of species is not direct, 

 but indirect, through its selective action on the already 

 existing variations of the members of a given race. 



Coming now to the second part of the problem, the heredi- 

 tary factor, we see, as has been pointed out many times 

 before, that these variations are given qualities, being due 



