6 BIOLOGY AND HUMAN LIFE 



make sure that each kind has its own name, and that a given 

 name stands always and everywhere for the same kind. This 

 work is not only interesting for those who like that sort of 

 thing, but it is also of great value to other workers. It is im- 

 portant to know, for example, when a farmer complains of some 

 insect or mildew injuring his crop, exactly who the enemy is, 

 and not to confuse him, from slight resemblances, with another 

 insect or mildew that may be harmless. Hundreds of situations 

 are constantly arising in which it is important to know to what 

 group a particular individual belongs, or whether a given plant 

 or animal species has ever been described and named before. 

 So exact description, classification, and naming are well worth 



while. 



Another branch of study concerns itself with the places upon 

 the earth where each kind of living thing is to be found, or un- 

 der what conditions it lives. Still another study has to do with 

 the kinds of living things that existed upon the earth in ancient 

 times, as may be learned from the remains in the rocks (fossils) 

 and coal beds, or perhaps preserved in the glaciers, or ice fields, 

 of Greenland and Siberia. 



Many people concern themselves with the study of structure 

 and arrangement of parts in plants or animals. Others, again, 

 are more interested in what living things do ; and people were 

 interested in that long before there was any systematic science 

 of biology. In modern times more and more attention is being 

 given to questions about how living things carry on the various 

 processes and activities that distinguish them from non-living 

 things. How do plants get food ? How are moths attracted by 

 light? How does vaccination prevent disease? How do mi- 

 grating birds find their way? How do seedless plants repro- 

 duce? Hundreds of questions are constantly coming to mind. 



Many people are chiefly interested in such questions as How 

 came there to be all the different kinds of plants or animals? 

 What makes different kinds resemble each other, for they are 

 not altogether different? What brought about the changes in 

 the inhabitants of Europe or North America during the past 



