480 THE INDIVIDUAL AND THE RACE: 



thus persist after the inducing conditions have ceased to 

 operate. They may be illustrated by the tanning of the skin 

 under a tropical sun, or by the fattening of cattle, or by a 

 callosity due to pressure. They are dints due to peculiarities 

 in nurture, and have not been convincingly shown to be 

 transmissible as such or in any representative degree. 

 Finally, it may be noted that development is the realisation 

 of the normal inheritance in appropriate nurture. 



§ 2. Heredity a Condition of Evolution. 



Heredity is not so much a factor in evolution, as a condi- 

 tion of evolution. There would be heredity though there 

 were no evolution, but there could be no evolution if there 

 were not heredity. What is the role of Heredity ? 



(a) Heredity involves arrangements which secure the per- 

 sistence of a specific dynamic organisation — holding fast that 

 which is good. This role is achieved by a simple device — 

 the continuity of the germ-plasm or essential germinal mate- 

 rial, a luminous conception mainly due to Galton and Weis- 

 mann. It amounts to this, that in the course of development, 

 often very early, some germinal material containing the in- 

 tact inheritance is kept apart from specialisation and goes 

 to form the germ-cells which become the starting-points of 

 another generation. As Galton pointed out, in development 

 the bulk of the germinal material of the fertilised egg-cell 

 goes to form the ^ body ' of the embryo, undergoing in a most 

 puzzling way differentiation into nervx and muscle, blood, 

 and bone ; but a certain residue is kept apart from the devel- 

 opment of the ^ body ' to form the primordium of the repro- 

 ductive organs of the offspring, whence will be launched in 

 due time another similar vessel on the adventurous voyage 

 of life. Thus in a sense the child is as old as the parent, 



