INTRODUCTION. 3 



its parts." On an earlier page of the same chapter, 

 Lamarck thus formulates the laws of organic evolu- 

 tion, to which his name has been attached. 



First law. " In every animal which has not passed 

 the time of its development, the frequent and sustained 

 employment of an organ gradually strengthens it, de- 

 velops and enlarges it, and gives it power proportional 

 to the duration of its use ; while the constant disuse 

 of a like organ weakens it, insensibly deteriorates it, 

 progressively reduces its functions, and finally causes 

 it to disappear." 



Second law. "All that nature acquires or loses in 

 individuals by the influence of circumstances to which 

 the race has been exposed for a long time, and in con- 

 sequence of the influence of the predominate employ- 

 ment of such an organ, or of the influence of disuse of 

 such part, she preserves by generation, in new indi- 

 viduals which spring from it, providing the acquired 

 changes be common to both sexes, or to those which 

 have produced new individuals. " 



We have here a theory of the origin of characters ; 

 viz., of the increased development or loss of parts as 

 a result of use or disuse. We have also the theory 

 that the peculiarities thus acquired are transmitted to 

 the succeeding generation by inheritance. 



The next formal statement of the efficient cause of 

 organic evolution was presented by Messrs. Charles 

 Darwin and Alfred R. Wallace in I859. 1 The cause 

 assigned is natural selection, and Mr. Darwin thus 

 states what is meant by this expression in his work 

 The Origin of Species.' 1 " If under changing conditions 

 of life organic beings present individual differences 



1 Proceedings of the Linnean Society of London. 



2 Ed. 1872, p. 102. 



