WHAT IS BIOLOGY? 7 



million years or more? What has caused ancient types of 

 plants and animals to disappear? How did existing species 

 originate? How came plants and animals to fit in so beauti- 

 fully into their particular living conditions? 



There are always men and women, boys and girls, who like to 

 ask practical questions about everything that happens. What 

 difference does it make if caterpillars do have biting jaws, or if 

 clover plants have little lumps on their roots? What can we 

 do about it ? What should we do about it ? 



It is impossible for everybody to think of all these questions, 

 much less to get the answers to all. The more we find out, the 

 more questions arise. So, more and more, people are choosing 

 just what particular questions or classes of questions they will 

 specialize in. Yet every one of us can learn some of the more 

 important questions in each department, and something about 

 why they are important, without becoming specialists. 



5. What makes biology interesting? It is impossible to say 

 beforehand just what will interest a certain person. Some of us 

 go in for postage stamps, while others prefer Chinese puzzles or 

 music. A subject like biology, which covers so much of the 

 world we live in, has in it something of interest for almost 

 everybody. There are several million different kinds of plants 

 and animals ; this must interest those who care about collect- 

 ing, sorting, matching, naming. New species are being dis- 

 covered, classified, and named every year. Hundreds of men 

 and women are constantly hunting for new varieties. Plants 

 and animals occur under such a great variety of conditions, and 

 show such remarkable variety of structure and habit corre- 

 sponding to these conditions, that they are a constant source 

 of amazement. 



Many remarkable relations are found among the parts of any 

 given plant or animal, as well as among the different plants and 

 animals in a given region. Thus, a slight chemical change in 

 one part of the body may bring about a violent change in the 

 action of the heart or of the nervous system ; or the extermina- 

 tion of an insect in one region may have a striking effect upon 



