224 Education through Nature 



their environment. The natural environment, such 

 as food, temperature, and the like, is supposed to act 

 very much as the farmer acts when he selects those 

 animals in his herd that possess the characters which 

 he wishes to preserve and perpetuate. 



According to Darwin, the direct influence of the 

 environment has some permanent effect on the organ- 

 ism, as may also the influence of use or function of 

 different parts. Hence natural selection, which means 

 either life or death, is not solely responsible for organic 

 changes resulting in permanent species, but the chief 

 cause. 



Wallace, on the other hand, maintains that natural 

 selection is the sole cause of variation, thus denying 

 the permanent modifying influence of external factors, 

 as well as use or function. 



This theory of Wallace, regarding natural selection 

 as the sole cause of variation, has been strengthened, 

 in recent years, by Weismann, who has arrived at the 

 same conclusion from his studies in animal morphology, 

 especially embryology and cytology. Weismann's con- 

 tribution reduces itself down to a denial of the possi- 

 bility of transmission of acquired characters , and has 

 given to the theory of evolution a somewhat technical 

 meaning. Evolution, in this sense, means develop- 

 ment from within. Weismann postulates in the 

 germ-cells, from which living things spring, certain 

 living units, supposed to reside in protoplasm, more 

 particularly in the cell-nucleus. These, according 

 as they are made to vary among themselves, by an 

 internal struggle and survival, determine the charac- 

 ters of the fully formed being. 



Evolution, in this sense of development from within, 

 is now often assumed, not only by social philosophers, 

 but by psychologists. Writers on pedagogy often 

 assume it unconsciously, without considering what 

 share external influences may have in the forming of 



