1S2 GENETICS IN RELATION TO AGRICULTURE 



the specific relation of the determining factor to the character or modifica- 

 tion in question. 



Finally the induced change in the organism must reappear in succeed- 

 ing generations in the absence of the original factor which determined 

 its production. Other conditions in the life of the offspring must remain 

 unchanged. The change in question may exhibit a lesser degree in the 

 immediate descendants in the absence of the original stimulus, and in 

 succeeding generations it may become progressively less, but the critical 

 point is the determination of whether such a change is exhibited iji any 

 degree whatsoever by offspring produced in the absence of the original 

 stimulus. 



The Belief in the Inheritance of Acquired Characters. Lamarck 

 first stated clearly the belief in the inheritance of acquired characters, 

 and the part which, it has been supposed to play in the determination 

 of the characters of living beings as they exist today. From his observa- 

 tions, he formulated two laws, which he stated as follows according to 

 Elliot's translation: 



In every animal which has not passed the limit of its development, a more 

 frequent and continuous use of any organ gradually strengthens, enlarges and 

 develops that organ, and gives it power proportionate to the length of time it has 

 been so used; while the permanent disuse of any organ imperceptibly weakens 

 and deteriorates it, and progressively diminishes its functional capacity until 

 it finally disappears. 



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 ; 

 all these are preserved by reproduction to the new individuals which arise pro- 

 vided that the acquired modifications are common to both sexes, or at least to 

 the individuals which produce the young. 



It is a curious fact which has been pointed out by Lankester that 

 these two laws are mutually contradictory. The first law states that 

 adaptive changes occur when organisms are subjected to new environ- 

 mental conditions; the second states that such newly acquired characters 

 become a part of the heritage of the individual. In other words accord- 

 ing to the first law the old established characters of the organism are 

 unable to maintain themselves under new conditions; according to the 

 second law it is implied that acquired characters having a much less 

 extended history possess a permanence and stability not accorded to the 

 older established characters. It should be noted, however, that this 

 implication was not what Lamarck emphasized. He dwelt rather upon 

 the very gradual, "imperceptible" effects of use or disuse, for example, 

 in permanently changing characters. 



The belief in acquired characters is still held by some modern biolo- 



