148 Nature and Nurture 



yet, is whether some of the more ancient and stable 

 items in an inheritance may not have their vehicle in 

 the cytoplasm of the germ-cells, for this would not 

 be inconsistent with the proved fact that the genes of 

 the more variable characters are carried by the chro- 

 mosomes. 



It is probable that the progress of biology will lead 

 to a more generous appreciation of the evolutionary 

 importance of nurture. Of its individual importance 

 there is no doubt, for the degree to which factors in 

 the natural inheritance find expression depends on 

 the appropriateness of the nurtural conditions — 

 whether of surroundings, food, or function. The wan 

 and blind Proteus of the Dalmatian caves has the 

 hereditary capacity of developing pigment, but it 

 will not do so if it remains in the darkness which is 

 now its normal environment. If it is brought into the 

 light it soon darkens ; if it is reared from its youth in 

 the light, its eyes will be less degenerate than they are 

 in the caves. In young forms reared in red light, the 

 eyes may become seeing eyes. Numerous experiments 

 justify a growing appreciation of the importance of 

 nurtural conditions in individual development. A 

 character is a function of nature and nurture. But 

 there is still very little evidence to warrant belief in 

 the transmissibility of an individually acquired 

 "modification" as such or in any representative de- 

 gree. Goldfishes kept in complete darkness for three 

 years become blind, the retina undergoing serious 

 degeneration. This is an instance of a somatic modi- 

 fication following directly on a peculiarity of nurture, 



