64 THE FOUNDATIONS OF ZOOLOGY 



The belief that nature is inherited nurture so obviously fails to 

 throw light on the problem of fitness that most of the modern advo- 

 cates of this opinion claim no more than that nurture supplies the 

 raw material from which natural selection picks out and preserves 

 the good, the useful, the fit; while the bad, the injurious, the unfit, 

 is neglected; but I hope my- readers may find reason to ask whether 

 we can be sure that nurture has even this amount of influence. 



Living things are preeminently distinguished by what is best 

 expressed by the word fitness; they are adjusted to the world 

 around them in such a way as to force us to believe that the use 

 to which their organization is put has, in some way, been the con- 

 trolling factor in the production of the organization itself. There 

 is no escape from the belief that the adjustment of the eye to the 

 principles of optics, its fitness for vision, has, in some way, guided 

 and controlled its history; that it has come into existence for seeing, 

 or by seeing, or because it sees. Darwin and Wallace have shown 

 how the use of a part determines its structure through the extermi- 

 nation of the relatively unfit, and the survival of the relatively fit; 

 and I shall try, in another place, to show that this explanation is 

 adequate and satisfactory; but at present we are concerned only 

 with the opinion that the eye has been made, wholly or in part, 

 by seeing. 



Since the conditions of life often tend, as we have seen, to 

 modify organisms in such a way as to fit them for these very con- 

 ditions; since, for example, the trained eye sees more than the 

 untrained eye ; since, within certain limits, extra demands upon a 

 muscle make it more able to do the extra work, — may not the spe- 

 cific constitution of each organism have been produced in somewhat 

 the same way .? May it not be the inherited result of the influence 

 of the conditions under which its ancestors lived; preserved, it may 

 be, by natural selection.' Since the pine tree does not grow up 

 without the mechanical influence of its environment, may not the 

 inherited tendency to which its shape is due have been caused 

 by the direct mechanical action of the environment of past 

 generations ? 



This is a fair question, and if it were asked by a boy, or by one 

 unfamiliar with the subject, I should welcome it as a sign of intelli- 

 gent interest; but when it is asked by a naturalist, I can look at it 



