304 Relation of Use and Disuse to Evolution 



strengthens, develops, and enlarges that organ, and gives to it a power 

 proportional to the length of time it has been so used; while the per- 

 manent disuse of any organ imperceptibly weakens and deteriorates it, 

 and progressively diminishes its functional capacity, until it finally 

 disappears. 



" Second Law: All the acquisitions or losses wrought by nature on 

 individuals, through the influence of the environment in which their race 

 has long been placed, and hence through the influence of the predominant 

 use or permanent disuse of any organ, are preserved by reproduction to 

 the new individuals which arise, provided that the acquired modifications 

 are common to both sexes, or at least to the individuals which produce 

 the young." 



In the edition of 18 15 he expanded the statement into 

 four propositions: 



"First Law: Life, through its own forces, continually tends to in- 

 crease the volume of every body which possesses it, and to increase the size 

 of its parts, up to a certain limit determined by life itself. 



** Second Law: The production of a new organ in an animal body 

 results from a new need supervening and continuing to make itself felt, 

 and from a new activity which this need arouses and maintains. 



"Third Law: The development of organs and their functional ca- 

 pacities are constantly in ratio to the use which they receive. 



" Fourth Law: Everything which has been acquired, impressed upon, 

 or changed in the organization of individuals during the course of their 

 life is preserved by generation and transmitted to the offspring of those 

 which have undergone these changes." 



Aside from the rejection of the general theory of evolu- 

 tion by Cuvier and others, misunderstanding centered on 

 the second law; and controversy as to the facts assumed 

 in the fourth law has continued to the present moment. 

 For the rest, the meaning is not only unambiguous but quite 

 in accord with common observation and common reason. 

 Lamarck elaborated his theory, however, to include other 

 factors which he took to be of significance in bringing about 

 the modification of species. For example, he drew a dis- 

 tinction between the action of the environment upon plants 

 and lower animals, and its action upon higher animals, those 



