414 THE GERM-PLASM 



ever, that he has overlooked the fact that the transformation of 

 a species, as well as the preservation of its constancy, are based 

 upon natural selection, and that this is incessantly at work, 

 never ceasing for a moment. 



From what was said in the chapters on the struggle of the 

 determinants of the two parents in ontogeny, and on the ' re- 

 ducing-division ' of the germ-plasm which is indispensable in 

 amphimixis, it follows that by means of the latter process fresh 

 combinations of the possible variations in a species must con- 

 stantly be produced. On the one hand, the germ-plasm of a 

 new individual produced by amphimixis never receives more 

 than half the ids of each parent — and these are differently 

 selected and arranged in each case ; and on the other, the co- 

 operation of the ids of both sides would not always strike an 

 average in all parts of the new organism, but each part would 

 resemble that either of the father or the mother in proportion to 

 the number and controlling force of the individual homologous 

 determinants ; the resultant of the co-operating forces may be 

 different in different parts. 



Although the process of amphimixis is an essential condition 

 for the further development of the species, and for its adaptation 

 to new conditions of existence amongst the higher and more 

 complicated organisms, it is not the primary cause of hereditary 

 variation. By its means those specific variations which already 

 exist in a species may continually be blended in a fresh manner, 

 but it is incapable of giving rise to new variations, even though 

 it often appears to do so. 



When it first occurred to me that sexual reproduction was 

 necessary to produce the variations required for the action of 

 selection, I imagined that its influence upon the germ-plasm was 

 still more powerful. Since all differences — even the qualitative 

 ones — are ultimately of a quantitative nature, and as the union 

 of the primary constituents of the parents may either strengthen 

 or weaken a ' character,' I imagined that the combination of very 

 strong primary constituents for the same part in both parents 

 would not only cause the part to reappear especially markedly in 

 the child, but would also double the strength of the primary 

 constituents of the part in the germ-cells of the child ; and thus 

 the continued intercrossing of offspring in which this part is 

 strongly developed, might cause it to be increased more and 

 more, so that it exhibited far more than an ordinary individual 



