482 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 in 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- 
Digitized by Microsoft® 
