226 Evolution and Adaptation 



citing some cases amongst plants that have been changed 

 directly by the action of the environment. He says that 

 since plants have no motions they have consequently no 

 habits, but they are developed by changes in their nutrition, 

 etc., and this brings about the superiority of some of the 

 vital movements over others. 



Amongst domestic animals Lamarck cites the case of the 

 dog:, that has come from a wild form like the wolf, but hav- 

 ing been carried into different countries has acquired different 

 and new habits, and this has led to the formation of new 

 races, such as the bulldog, greyhound, pug-dog, spaniel, etc. 



Lamarck's argument shifts so often back and forth from 

 animals to plants, that it is clear that in his own mind he did 

 not see any important difference between the action of the 

 environment on plants, and the use of the organs of the 

 animal. He gives in this same connection his oft-quoted 

 summary of what he calls the two laws of nature " which 

 observation always establishes." 



First Law. In every animal, that has not passed beyond 

 the term of its development, the frequent and sustained use 

 of any organ strengthens it, develops it, increases its size, 

 and gives it strength proportionate to the length of time of its 

 employment. On the other hand, the continued lack of use of 

 the same organ sensibly weakens it ; it deteriorates, and its 

 faculties diminish progressively until at last it disappears. 



Second Law. Nature preserves everything that she has 

 caused the individual to acquire or to lose by the influence 

 of the circumstances to which the race has been for a long 

 time exposed, and consequently by the influence of the pre- 

 dominant use of certain organs (or in consequence of its 

 continued disuse). She does this by the generation of new 

 individuals which are produced with the newly acquired 

 organs. This occurs, provided that the acquired changes 

 were common to the two sexes, or to the individuals that 

 produced the new forms. 



