68 ORGANIC EVOLUTION 



It is well known that both animals and plants change 

 constantly during their whole lives as a result of the effects 

 on them of the environment, and through the reaction upon 

 themselves of their own activity. Use strengthens a muscle 

 and disuse allows it to waste away. Some claim that, as 

 a matter of course, any such effect produced in one indi- 

 vidual will be handed down to his descendants, and that 

 here we have a most potent cause of evolution in the trans- 

 mission to the offspring of the modifications produced in 

 the parent. Favorable or poor conditions of nutrition pro- 

 duce great effects on individual plants and animals ; so also 

 do climatic conditions. Are these effects upon the indi- 

 viduals of one generation transmitted to their offspring of 

 the next generation ? If so, this inheritance of parental 

 modifications must have the greatest influence upon evolu- 

 tion. The matter needs careful scrutiny. 



Amono- the lower forms of living things, the unicellular 



O O O ' 



forms, many of which are so lowly that we cannot determine 

 whether they be animals or plants, among these lower forms 

 the inheritance of parental modifications is undoubtedly a 

 fact, as a single illustration will suffice to show. An Auurfia 

 is a lowly animal of microscopic size, consisting of a bit of 

 protoplasm with a single nucleus. It has no highly differ- 

 entiated organs, but the whole body takes part in the per- 

 formance of each function. When this animal reproduces, it 

 merely divides into two (or more) little Amoebcc, each of 

 which eats and grows again to the characteristic adult size, 

 when the process of division is repeated. The offspring are 

 merely parts of the original parent, and of course show in 

 themselves the features of oro-anization characteristic of this 



<^j 



parent. We can readily see that modifications of the parent 



