CHAPTER IV 



THE RAW MATERIALS OF 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 



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