THE HEREDITY OF ACQUIRED CHARACTERS. 1 



By L. Cu£not, 

 Professor of the College of Sciences at Nancy. 



An acquired character is a modification appearing in a plant or an 

 animal, at any age whatsoever, which is plainly the effect of an ex- 

 terior and accidental cause, of such nature that if this cause had not 

 intervened, the modification would certainly not have been pro- 

 duced. Acquired characters are legion. We will cite a few to fix 

 our conception of them and to illustrate the definition : The immun- 

 ity which follows an infectious disease; the sensibility to injections 

 of equine serum which is exhibited by the Tartar peoples nourished 

 by the milk and meat of the horse; the pigmentation of the bare 

 parts of the human skin exposed to the action of the open air and 

 especially of light rich in ultra-violet rays ; an accidental mutilation ; 

 the modifications presented by plants of the plain when transplanted 

 to Alpine regions; the enlargement and the strength of a muscle 

 systematically exercised; everything which man learns during his 

 lifetime, such as his language, his writing, any form of sport, etc. 

 It is understood that an acquired character is just the difference be- 

 tween the normal condition, or the condition which served as the 

 point of departure before the action of the modifying cause, and the 

 new condition after the action of that cause. 



In order to consider a character as acquired, it is necessary that 

 the relation of cause to effect should be evident, either when the 

 cause has been made to act experimentally, or when the observation 

 of nature has been made with the care and exactness of an ex- 

 periment (which is rare). It is well known that for a long time, 

 until about 1883, it was believed without question that the acquired 

 character was hereditary to a more or less marked degree; that is, 

 that parents having acquired a certain thing would procreate a 

 generation presenting more or less completely, at least in the shape 

 of an indication or a rudiment, the acquired bodily modification, in 

 the absence of the exterior cause which had produced it in the- 

 parents. Lamarck and his school made of this heredity of acquired 



1 Translated by permission from the Revue G£n6rale des Sciences, Oct. 15, 1921. 



335 



