420 ANIMAL BIOLOGY 



volved, the answer would still be clear. Experts tell us that without 

 the services of insect-eating and seed-eating Birds, successful 

 agriculture would soon be impossible, and the destruction of the 

 greater part of our vegetation would also result. One caterpillar 

 during its lifetime of less than two months can consume three- 

 quarters of a pound of leaves, or nearly ninety thousand times its 

 original weight. Birds are 'the winged wardens of our farms." 

 Their help is needed in the struggle. 



In truth, it is dangerous for Man to upset the intricate balance 

 of the economy of nature by the reckless destruction of plant or 

 animal without taking thought for the morrow — without inten- 

 sive study of the far-reaching consequences which may follow from 

 the breaking of one link in the chain of the interrelationships of 

 organisms. The destruction even of certain Protozoa and other 

 microscopic life may seal the fate of Fish valuable for food. 

 (Figs. 24, 220, 266.) 



D. Constructive Biology 



The great living heritage which we have received will be per- 

 manently impaired for posterity, even though useless waste is 

 stopped, unless the highly complex problem of conservation is at- 

 tacked constructively in the light of modern biological knowledge. 

 Merely to hold Nature's bonus unimpaired, crucial as that is, will 

 not adequately meet the requirements of increasing populations 

 with the attendant demands of complex civilized life. Few seem to 

 realize that the whole of our business life takes root in nature. All 

 of our progress and prosperity is predicated on the abundance of 

 our natural resources and the manner in which we develop them for 

 Man's use. Methods of raising crops and domestic animals which 

 were sufficient for primitive communities are entirely inadequate 

 to satisfy modern conditions. 



Indeed, the state of civilization of a people is closely related to its 

 success in developing plants and animals for particular needs. One 

 hears of new 'creations,' but often fails to recall that Man can 

 merely direct the laws of inheritance, and this he can do only 

 by intensive investigations of the principles underlying heredity. 

 Certainly the most important recent contribution of biology is the 

 discovery of the general method of transmission of characters from 

 generation to generation, common to all living things, which has 

 established the new biological science, genetics. To-day, as we 



