APPENDIX A 355 



higher animals which produce few offspring nevertheless contain 

 an altogether disproportionate multitude of germ-cells. Material 

 is thus provided for a germinal selection more real than that 

 which Weismann sought to demonstrate l a germinal selection 

 strictly comparable to the selection of individuals which follows 

 later. Probably a similar form of selection prevails among the 

 somatic cells. This hypothesis may appear far-fetched at first 

 sight; but, when we remember (1) the apparently wasteful 

 superabundance of germ-cells in the higher animals, (2) the fact 

 that somatic cells usually perish under the action of the environ- 

 ment before they alter their hereditary tendencies, (3) that all 

 species must perish unless their germ-cells possess a like in- 

 susceptibility, (4) that this insusceptibility must have resulted 

 from Natural Selection ; and (5) that in this case Natural 

 Selection can operate with greater advantage when it selects 

 germ -cells than when it selects individuals, the truth of the 

 hypothesis is rendered at least possible. 



It is obvious that an immense amount of confusion has been 

 caused in biological discussion by an inaccurate use of the terms 

 inborn and acquired, or their equivalents. An endeavour to 

 gain the clearest possible perception of their meanings will there 

 fore be well worth our while. Living beings develop from the 

 germ mainly under the influence of three distinct stimuli, that 

 operate from the external world nutrition, injury, and use. 

 Other stimuli, such as temperature, exist, but they are com- 

 paratively unimportant, and we need not pause to discuss them. 

 To take the example of the human being ; up to the time of 

 birth the infant develops wholly or almost wholly under the 

 stimulus of nutrition. Subsequently some of his structures 

 continue to develop under this influence for example his organs 

 of generation, his hair, his teeth, and his external ears. But as 

 regards other of his structures, though nutrition continues to 

 supply the materials for growth, it ceases to supply the stimulus. 2 

 No matter how well he be fed, his limbs for example do not 

 develop much beyond the infantile standard except they be used. 

 If at any time the individual be injured, as by a cut, and 

 survives, the wound supplies the stimulus for the growth that 

 occurs during the process of healing. 



Now, when we say that one individual is innately like or 

 unlike another, we mean, in effect, that the likeness or unlike- 

 ness is due to a similarity or dissimilarity in the germ-plasms 

 whence the individuals sprang. On the other hand, if we say the 

 two individuals agree or differ in their acquirements, we mean 

 that the stimuli under which they developed have been similar 

 or dissimilar in kind or degree. Here the words inborn and 

 acquired are used quite correctly. 



1 See 158. 



2 See note p. 272. 



