144 THE ORIGIN AND EVOLUTION OF LIFE 



be increasingly similar to the adults of antecedent genera- 

 tions, which is frequently the case but unfortunately for the 

 Lamarckian explanation is not invariably the case. In many 

 parts of the skeleton chromatin development and degeneration 

 so obviously follow bodily use and disuse that Cope was led to 

 propose a law which he termed baihmism (growth force) and to 

 explain the energy phenomena of use and disuse in the body 

 tissues as the cause of the appearance of corresponding energy 

 potentialities in the chromatin. In other words, he believed 

 that the energy of development or of degeneration in the bodily 

 parts of the individual is inherited by corresponding parts in 

 the germ. Similar opinions prevail among most anatomists 

 (c. g., Cunningham) and among many palaeontologists and zo- 

 ologists {c. g., Semon). 



The opposed explanation, the pure Darwinian,^ as restated 

 by Weismann and de Vries, is that the genesis of new form and 

 function is to be sought in the germ cells or chromatin. This is 

 based upon an hypothesis which is directly anti-Lamarckian, 

 that the actions, reactions, and interactions which cause cer- 

 tain bodily organs to originate, to develop, or to degenerate, 

 to exhibit momentum or inertia in development, do not give 

 rise to corresponding sets of predispositions in the chromatin, 

 and are thus not heritable. According to this explanation, 

 body cell changes do not exert any corresponding specific in- 

 fluence on the germ cells. All predispositions to new form and 

 function not only begin in the germ cells but are more or less 

 lawless or experimental; they are constantly being tested or 

 tried out by bodily experience, habits, and functions. Techni- 

 cally stated, they are "fortuitous" or chance variations, fol- 

 lowed by selection of the fittest variations, and thus giving 

 rise to adaptations. Thus Darwin's disciple, Poulton, also de 



' Cf. Preface, p. xiv. 



