THE WONDERS OF LIFE 



the phenomena of heredity and adaptation in definite 

 laws and arrange these in series, I drew a distinction 

 between conservative and progressive heredity (chapter 

 ix., History of Creation). Conservative heredity, or the 

 inheritance of inherited characters, transmits to pos- 

 terity the morphological and physiological features 

 which each individual has received from his parents. 

 Progressive heredity, or the inheritance of acquired 

 characters, transmits to offspring a part of those features 

 which were acquired by the parents in the course of their 

 individual lives. The chief of these are the characters 

 that are caused by the activity of the organs themselves. 

 Increase in the use of the organs causes a greater access 

 of nourishment and promotes their growth; decrease in 

 the exercise of organs has the contrary effect. We have 

 examples at hand in the modification of the muscles or 

 the eyes, the action of the hand or throat in painting or 

 singing, and so on. In these and all the arts the rule 

 is: Practice makes perfect. But this applies almost 

 universally to the physiological activity of the plasm, 

 even its highest and most astounding function — thought ; 

 the memory and reasoning capacity of the phronema are 

 improved by constant exercise of the cells which com- 

 pose this organ, just as we find in the case of the hands 

 and the senses. 



Lamarck recognized the great morphological signifi- 

 cance of this physiological use of the organs, and did 

 not doubt that the modification caused was transmitted 

 to offspring to a certain extent. When I dealt with this 

 correlation of direct adaptation and progressive heredity 

 in 1866, I laid special stress on the "law of cumula- 

 tive adaptation" {General Morphology, ii., p. 208). "All 

 organisms undergo important and permanent (chemical, 

 morphological, and physiological) changes when acted on 

 by a change in its life-conditions, slight in itself, but 

 continuing for a long time or being frequently repeated." 



368 



