xivl THE POWER OF HEREDITY 



the primordial epoch of life (when, as we may say, the organic world 

 was young), it must have grown with time, accumulating and in- 

 creasing in successive generations, it wall be possible to reconcile 

 the theory of the " permanent impressionability " of organisms 

 (i.e. to the stimuli exerted on them by external conditions) with 

 belief in the all but complete immutability of species now living. 



That at the present time the power of heredity is such as to put 

 great obstacles in the way of variation is a fact which cannot be 

 denied ; that in the past it had not always the same force cannot 

 be directly proven, but can easily be credited ; and that the further 

 we go back towards the origin of life the less strong it must have 

 been, is only a logical sequitur of the admitted strength of the force 

 heredity now exerts. 



Thus during the infancy of the organic world, there being then 

 no power to counteract the conservation of new characters acquired 

 by organisms, the latter must have been not only susceptible of 

 considerable morphological malleability during their lifetime, but 

 must have also been capable of transmitting to their descendants 

 any new characters of an advantageous kind they had acquired. 



The period of a human lifetime reproduces on a small scale what 

 must have happened in gigantic proportions during the evolution of 

 living beings. No one can deny that infancy has peculiarities which 

 are not possessed by old age. And it is equally true that during the 

 first period of life the force of habit is less powerful than in adult age. 

 In early youth animals can be domesticated or tamed, children learn 

 with facility, and even their limbs are pliable and capable of modi- 

 fication. With age heredity acts more strongly, instincts prevail, 

 and adaptation to new conditions of existence and to new ideas 

 become more difficult ; in a word, it is much less easy to combat 

 hereditary tendencies. 



What can have happened at an epoch when heredity did not 

 exist is hard to infer with precision. In the absence of this factor in 

 the evolution of living beings, almost any change or variation in the 

 latter must have been possible. There is even no necessity to sup- 

 pose that in the remotest past the offspring need have been neces- 

 sarily similar to its progenitors. Every new generation of organ- 

 isms might differ from that which preceded it, so that " species," 

 in the sense in which the word is now used, may have been then a 

 term without meaning. 



In that epoch, geologically of the remotest antiquity, light, heat, 

 drought, abundant rains, winds, the nature of the soil, colours, the 

 stimuli of insects, et similia, may all have contributed to promote 

 modification in the organisms placed under their influence. This 

 would have been the Plasmative Epoch — the epoch of the auto- 

 creation of species. 



Thus I attribute to such causes not only the special structures 



21 Q 



