vii LAW AND PRINCIPLE 187 



the eminent French zoologist, who devoted many years 

 of his life to studies of the problem of the origin of species. 

 The main points of the principle published by Lamarck 

 in 1801 are that animals may have their structures 

 modified by external conditions or by continued use or 

 disuse, and that the succeeding generation inherits the 

 modification. On this principle, the long neck of the 

 giraffe is explained by the constant straining of genera- 

 tions of the animal to reach the tender shoots at the tops 

 of trees, and the splay foot of the camel by continued 

 walking on desert sands. The two fundamental laws 

 of adaptation and heredity formulated by Lamarck to 

 account for the production of new species were stated 

 by him as follows : 



1. In every animal which has not got beyond the period of 

 developing, the frequent and sustained use of any organ gradually 

 strengthens it, develops it, enlarges it, and gives it a power 

 proportionate to the duration of the using of it ; while the con- 

 tinued disuse of this or that organ imperceptibly weakens it; 

 and it deteriorates, loses its power by degrees, and finally 

 disappears. 



2. All that Nature has allowed individuals to gain or lose by 

 the influence of the circumstances to which their race has been 

 exposed for a long time, and consequently, by the effect of pre- 

 dominant use of this organ or continued disuse of that, is con- 

 served in the new individuals who spring from them, and who, 

 therefore, find themselves better adapted than their ancestors, 

 if the conditions of existence have not changed. 



Lamarck's principle thus states not only that variations 

 may be produced by the influence of external conditions, 

 or by exercise, but also that the new characters thus 

 acquired are inherited by succeeding generations. How 

 far the principle supplies the true cause of natural 

 processes has been a matter of much discussion in recent 

 years, but the proof of the inheritance of acquired 



