33G ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



characters the pivotal point of their theory of evolution and of 

 adaptation. Darwin and Herbert Spencer also fully accepted it, 

 It is useless to insist on the capital importance of the phenomenon 

 for the general explanation of adaptations. Without for the moment 

 asking ourselves why, we can see that the reactions of the individual 

 to any exterior action whatever have very generally an adaptive 

 or protective value: A tanned skin is less penetrable by ultra- 

 violet rays; immunity protects against a new attack of disease; a 

 muscle, a joint, exercised within certain limits, functions more 

 easily and more effectively than before the training. If the 

 heredity of acquired characters exists, to however slight a degree, 

 we possess the key to an enormous number of adaptations. If 

 it does not exist, we must find other explanations. 



This is not alone a question which interests speculative scholars 

 isolated from the world ; it is also a question of importance to society. 

 When it is repeated to the public at large that the practice of sports, 

 even to excess, prepares for vigorous new generations, the idea is 

 certainly entertained that the " all-round athletes " or even those 

 who are abnormally specialized by exercise, will bequeath to their 

 descendants at least a rudiment of their acquired qualities. It is 

 surely the opinion of breeders, who believe that the effects of the 

 training of race horses, of the good or bad nutrition of cattle, are 

 transmissible in certain measure. 



It was not until 1883 that, for theoretical reasons whose value has 

 not been diminished by time, Pfliiger, 2 on the one hand, and Weis- 

 mann, 3 on the other (Essay on Heredity, read at a public meeting 

 when he was tendered the position of vice rector of the University 

 of Freiburg, on June 21, 1883), were led to formally doubt this 

 heredity. Weismann presented arguments of such force — he exam- 

 ined the whole question with so penetrating a critique — that it is 

 only just to give him the credit for the change of opinion which 

 dates from his lecture of 1883. But if he convinced many biologists, 

 he encountered also unyielding opponents so powerful that for 37 

 years, in spite of numerous and remarkable researches, the heredity 

 of acquired characters has remained a problem continually presented. 

 It may be said that all the experimental proofs which have been 

 contributed to the support of the transmission (E. Fischer, Stand- 

 fuss, Kammerer, etc.) are mediocre and do not lead to conviction, 

 or are susceptible of criticism and interpretations which weaken their 

 demonstrative value, or, indeed, are frankly contradicted (as in the 



- Tfliiger, Ueber den Einfluss der Schwerkraft auf die Theilung dor Zellen und auf die 



Entwicklung des Embryo, Arch. f. Phys., t. XXXII, 18S3, p. 68. 



•Weismann, Essais sur l'II£r6dite' et la selection naturelle, trad, de Varigny, Paris, 

 1802. 



