MEANING OF REPRODUCTION 11 



needs exercise, we say, in order to keep well; but 

 exercise is outgo. It destroys some of that which has been 

 built up. You will find, however, that this alternate 

 building up and tearing down results in a better self than 

 the pure self-building. Too much income, without 

 activity, begets softness and stagnant life. Yet in youth 

 the building up must be more rapid than the tearing down. 

 This makes growth. 



There is still another way in which this excess which is 

 stored up in youth may be used. Most plants and animals 

 as they approach maturity cease to use the whole of their 

 income for their further growth. Instead, they give off 

 portions of themselves, which finally become entirely 

 separate and form other individuals of the same kind. 

 This is called reproduction. It is a kind of growth; but it 

 is growth beyond the limits of the individual. It starts a 

 new individual at the expense of the old. Some of the food 

 which might have gone into the parent goes to build up 

 the new individual. We have found two ways then 

 whereby the individual gets rid of some of its income. 

 These therefore must check its over-growth. They are 

 activity and reproduction. 



4. What Makes an Organism Reproduce? An organism 

 through its whole life has been selfishly laying up in its 

 body the greatest possible amount of material. What 

 could possibly cause it to change its behavior to the very 

 unselfish act of giving a portion of its income, and often a 

 very considerable part of its own body even, to a new 

 individual, whose future will be wholly distinct from it? 

 We have not found a full answer to this question; and yet 

 there are some interesting clues that help us to see how it 

 might have been caused. 



In the simplest kind of organism, a single globular 

 cell, all of the nourishment must be absorbed through the 

 outer wall or surface of the sphere. On the other hand, 

 the amount of nourishment necessary for it is determined 



