DARWINISM AND MODERN GENETICS 



evolution regard such claims as at best not proven and do not 

 feel justified in granting them an important place in the general 

 theory of evolution. 



It remains true, however, that evolution has produced many 

 phenomena which suggest quite strongly that the environment 

 is not wholly without influence on the nature of the variations 

 which occur. For instance, we often find that local races of 

 plants which live under peculiar environmental conditions ex- 

 hibit, as hereditary properties, characters exactly similar to those 

 which we would expect to be produced as developmental modi- 

 fications by the environment (Clausen and Hiesey, 1958). For 

 instance, alpine races often have short stems and long root 

 systems. These are hereditary qualities of the alpine race, as 

 can be proved by growing its seed in a lowland situation. On 

 the other hand, if seeds from a lowland race are grown in the 

 mountains, the resulting plants will be modified by the en- 

 vironment in the direction of the alpine type. There is a con- 

 siderable variety of data of this kind, and it appears to be quite 

 unreasoi able to suggest that the developmental modifications 

 which the environment can produce are quite irrelevant to the 

 evolutionary process. 



It is not necessary, however, to suppose that the environ- 

 ment acts by the direct induction of appropriate variation, in 

 the way suggested by Lamarck and Lysenko. It was pointed 

 out some twenty years ago, by both Soviet geneticists and others 

 (Schmalhausen, 1949; Waddington, 1940, 1942), that an al- 

 ternative mechanism is possible, and recently experiments have 

 been carried out which show that the process suggested can be 

 realized in practice (Waddington, 1957). 



If a heterogeneous population of animals is subjected to 

 some new environmental stress, this will produce in them a 

 variety of developmental modifications. Some of these modifi- 

 cations may be of adaptive value. There will then be natural 

 selection favouring hereditary potentialities for reacting in an 

 adaptive manner to the environmental stress. As generations 

 pass, and selection proceeds, the population will eventually 

 come to consist of individuals all of whom will in the new 

 environment develop the corresponding adaptive phenotype. 

 Now it is a general observation that developmental processes 



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