EVOLUTION AND HEREDITY 357 



heredity and they have also shown increasing specialization 

 to adapt them to environmental conditions. The Lamarck- 

 ians maintain that animals acquire characters in their 

 reactions to environment, that these are transmitted, and 

 hence that changing environmental relations cause evolution 

 and adaptation. Darwinians claim that there has been 

 evolution because the environment has selected variations, 

 and that there is adaptation because the variations which 

 best fit the environment are selected. For the former view 

 there is little or no evidence; for the latter there is increasing 

 support from experiment and observation. 



Professor Morgan in his recent book proposes a some- 

 what new method of selection as the basis of evolution. He 

 believes that selection does not operate on small fluctuating 

 variations but on numerous small mutations. 



"Evolution of wild species appears to have taken place 

 by modifying and improving bit by bit the structures and 

 habits that the animal or plant already possessed. Evolution 

 from this point of view has consisted largely in introducing 

 new factors that influence characters already present in the 

 animal or plant. ... In other words, the emphasis may be 

 placed less on the competition between the individuals of a 

 species (because the destruction of the less fit does not in 

 itself lead to anything that is new) than on the appearance 

 of new characters and modifications of old characters that 

 become incorporated in the species, for on these depends 

 the evolution of the race. 



" The mechanism of heredity has, I think, been discovered 

 discovered not by a flash of intuition but as the result of 

 patient and careful study of the evidence itself. With the 

 discovery of this mechanism I venture the opinion that the 

 problem of heredity has been solved. We know how the 

 factors carried by the parents are sorted out to the germ 

 cells. The explanation does not pretend to state how fact- 

 ors arise or how they influence the development of the 

 embryo. ... So, I repeat, the mechanism of the chromo- 



