CHAPTER IV 



THE RAW MATERIALS OP EVOLUTION 



Organic Progress Primarily depends on Variability — Darwin's Posi- 

 tion — Progress since Darwin's Day in Regard to Variation 



Variations more Abundant than even Darwin supposed — 

 Proportion between Frequency and Amount of Variations 

 — Correlation of Variations — Brusque Variations more Frequent 

 than was formerly supposed — Discontinuous Variations — 

 Mutations — Darwin's Position in Regard to Mutations — Origin 

 of Variations — Germinal Selection— Variational Stimuli — 

 Modifications or Acquired Characters — Indirect Importance of 

 Modifications — Modification-Species — Individual Plasticity — 

 Relation to Human Life. 



Organic Progress Primarily depends on 

 Variability. — The most difficult problem in bio- 

 logy — ^part of the persisting mystery of life itself — 

 is the innate changefulness which we often see 

 manifested in a family, a herd, or a seed-plot, when 

 we compare one generation with another. Of how 

 much interest and importance is this changefulness ! 

 for it is among the inborn variations of living 

 creatures that we find the raw materials of evolu- 

 tion. 



Evolution implies change — change along a defi- 

 nite line, and it also implies a certain continuity 

 throughout the change. Individual development, 

 the growing of the mustard-seed into the greatest 

 of herbs, the " minting and coining of the chick 

 out of the egg," is progressive change in which the 



97 7 



