LAMARCK'S EXPLANATION 515 



early scientists, plants and animals are changed by their en- 

 vironment, and these changes are then inherited by the offspring 

 and retained as long as the environment remains constant. For 

 example, according to this explanation, a plant, originally smooth 

 but having been induced to become hairy through exposure to 

 a drier chmate, will impart the hairy feature to the offspring, 

 which will maintain the modification until the environment so 

 changes that hairiness is lost. In this way the origin of new char- 

 acters and new species was explained. This assumes of course 

 that a change in any part of the plant is recorded in the sperms 

 and eggs of the plant and, therefore, transmitted to the progeny. 



Lamarck's Explanation. — Lamarck, a noted French natur- 

 alist whose views were published first in 1801 and in an en- 

 larged form in 1809, offered the explanation which he called 

 '' Appetency," meaning desire. His explanation was based upon 

 the observation that the organs of men and other animals are 

 enlarged and strengthened by use and particularly by con- 

 scious use. For example, it is common observation that one's 

 muscles enlarge and become stronger with proper use, while, 

 on the other hand, with lack of use they decrease in size and 

 strength. Long continued disuse may even result in the loss 

 of an organ. 



There are three ideas involved in Lamarck's explanation. 

 First, his explanation assumes that the environment of animals 

 and plants has been constantly changing, so that they have been 

 constantly subjected to changes in temperature, moisture, light, 

 nutrition, etc. Second, he believed that all living things have 

 come from preexisting forms as a result of changes which were 

 repponses to changes in the environment that made a new mode 

 of life necessary. Thus the neck of the giraffe lengthened as 

 a result of the animal's effort to reach leaves on high branches. 

 Also the form of the body of reptiles, such as snakes, which 

 glide over the ground and conceal themselves in the Grass, is 

 due to the mode of life which these animals have adopted. By 

 repeated efforts of the animal to elongate in order to pass 

 through small spaces, the body became extremely elongated and 

 very narrow, and since long legs would raise the body too high 

 from the ground and short legs would not move them rapidly 

 enough, legs, vestiges of which are still in their plan of organiza- 

 tion, were finally lost and another means of transportation was 



