THE CHILD AND HEREDITY 163 



but amid dull, colourless surroundings, ceases to be bright 

 green, and becomes a sombre grey. Put him among 

 foliage again and his green soon returns. It cannot be 

 said that the green foliage has caused his colour to change. 

 It is more correct to say that he has the power of changing 

 his colour to suit his environment. If the frog happens 

 to be blind, no change of colour takes place ; so that it is 

 by the help of the eye and the nervous system that the 

 change is effected." l The power of reaction must be 

 present. The true cause of the change is within ; outer 

 circumstance incites it into operation. " In fact an external 

 condition can do nothing but bring to light some latent 

 quality" ; or, as Weismann puts it, "Nothing can arise 

 in an organism unless the predisposition to it is pre-existent, 

 for every acquired character is simply the reaction of the 

 organism upon a certain stimulus." 2 Thus the denial of 

 the inheritance of acquired qualities and the assertion of 

 the inheritance of all other characteristics go hand in hand. 

 They are both consequences of the view that the environ- 

 ment can only furnish the occasion^ that is, the incentive 

 and means of organic development. 



Now, this view of the significance of heredity and of 

 the subordinate, though necessary, role of the environment 

 carries with it most important consequences for the study 

 of the child and the conditions of his development. The 

 first of these consequences, it is manifest, is that if we 

 accept this theory in its full extent, we must conclude that, 

 at least so far as his organic structure is concerned, the 

 human being must be regarded as in some manner latently 

 or potentially present even in the very lowest form of 

 animal life. Biologists do not hesitate to draw this con- 



1 Headley's Problems of Evolution, p. 49. 2 Ibid., p. 50. 



