VARIATION 435 



change in some particular kind of metabolism may reverberate 

 through the whole body. 



Another important idea is that of temporal variations, that is to 

 say, alterations in the ' time ' or rate or rhythm of metabolic pro- 

 cesses, or in the duration of particular phases in the life-cycle. 

 Many changes of great adaptiveness are probably due to the length- 

 ening out of one chapter and the telescoping of another. In the 

 influence of internal secretions in backboned animals there is a 

 known method of effecting these changes in 'time'. 



Of great importance for our interpretation of evolution is the 

 growing body of evidence that variation is often a much more 

 definite organic change than was formerly supposed. There are 

 many illustrations of progressive variation along a definite line, 

 orthogenesis. Instances of mutations are accumulating, and if 

 mutations come they usually come to stay. This also lessens the 

 element of the casual and the need for over-burdening Natural 

 Selection with the task of sifting from amid a crowd, and of ac- 

 cumulating minute increments. Furthermore, variations occurring 

 in a unified individuality are not likely to be stable unless they are 

 congruent with the organisation already established. Thus there 

 seems little warrant for talking about evolution as a "chapter of 

 accidents ". 



It may well be that our conception of variability is fallaciously 

 abstract unless we recognise that germ-cells are living organisms of 

 great complexity telescoped down into a one-cell phase of being, 

 and that they make essays in self-expression which we call varia- 

 tions. These blind experiments of the germ-cells are submitted 

 to the developing and adult organism to be tested in actuality. 



