364 Appendix B 



tinguish the two classes. In the studies of variations which 

 have hitherto been made there has been no attempt to distin- 

 guish between them. When it is found that the length of the 

 beaks of birds varies widely with the climate, or that the length 

 of the wings or legs shows variations on either side of a mean, 

 it has been assumed that these are innate differences, and there- 

 fore, if selected, are matters of heredity. Most of the signifi- 

 cance attached to the statistical study of variation mentioned in 

 an earlier chapter depends upon this assumption. But it is at 

 least as probable that the variations are simply due to the action 

 of the environment, habit, or use, and hence purely acquired. 1 

 Most of the studies of variation which have been made, up to 

 the present, have consisted in recording variations, either great 

 or small, but without attempt to determine to what extent they 

 are really congenital, and to what extent due to the action of the 

 environment upon the individual. Considering the great differ- 

 ence in the relation of the two classes to the problem of evolu- 

 tion, it is evident that no very clear results will be reached until 

 the two types of variation are more carefully separated. 



" Be this as it may, it is certain that the environment lias a 

 great influence upon the development of each individual, in- 

 dependent of his inherited characters. It is equally evident 

 that these acquired characters must change with every change 

 of condition or habit. If an animal acquires a new food plant 

 or a new habitat, if he learns a new method of protecting him- 

 self, or if a plant starts to grow in a soil different from that in 

 which it has hitherto lived, these changes will, of course, 

 produce their effect, and acquired variations will result. Now, 

 as we have seen, it is difficult to believe that these variations 

 will so affect the germ plasm as to be transmitted to the next 

 generation, but it is equally clear that if the next genera- 

 tion should be placed under the same conditions it would 

 independently develop similar variations, entirely independent 

 of heredity. So long as the environment remains the same, 

 each generation will develop, after its birth as an individual, 

 the same sort of acquired variations. These, appearing regu- 



1 Cf. the positions taken above, pp. 331 ff. J. M. B. 



