236 THE MEANING OF EVOLUTION 



and without accounting for them, he built his own 

 theory of evolution. He realized his weakness, and 

 acknowledged it in his book. He probably did not 

 anticipate how insistently later biologists would de- 

 mand an explanation that would account for this 

 variation. In his later work, responding to this criti- 

 cism, Darwin originated a theory which he called 

 Pangenesis. He believed that when an adult animal 

 had responded to his environment and acquired a new 

 character he could transmit this character to his off- 

 spring. At that time no one doubted this fact. The 

 whole theory of Lamarck was based on the assump- 

 tion that this could be done. Darwin suggested that 

 every organ of the body threw off minute particles, 

 which he called pangenes. These little bodies, car- 

 ried by the blood, were taken up by the egg cells or 

 sperm cells, and the latter cells determined the future 

 development. Consequently, the character of the new 

 individual was determined by the parental pangenes. 

 In this way the gain acquired by one generation could 

 be passed on to the next. This theory was purely 

 speculative. He never pretended that there was the 

 faintest corroborating evidence visible to the micro- 

 scope in the organ, in the blood, or in the germ cell. 

 It was not an accounting for what is, but for what it 

 seemed possible to him might be. 



This theory of Pangenesis, in the shape in which 



