6 ELEMENTARY BIOLOGY 



other plants and animals, for it is an important truth of life 

 that no being lives by or for itself alone. The life of every 

 plant and of every animal is tied up closely with the lives of 

 many other living beings. The life of man, which is to us 

 so important and so interesting, is most closely bound up with 

 the lives of other beings. Indeed, that is just the reason why 

 we cannot understand human life without a study of biology. 

 So it is possible to study this subject from the point of view 

 of man, and that should be the most interesting. 



We could take up, one after another, the important activities 

 of a human being that have to do with maintaining life and 

 with enjoying life, and learn the relations of these activities 

 to one another and to the world about us. Or we could begin 

 by inquiring as to the causes of the various events that we 

 find making up our lives. One way of studying would be 

 just as good biology as the other. We must select, however, 

 the way that has been found to be most convenient and profit- 

 able, all things considered. 







