522 
BIOLOGY AND HUMAN PROGRESS 
you should prepare yourselves by thorough study to have a 
part in this great work. 
In this chapter a brief account of the value and character 
of new discoveries in biology will be given. The examples 
selected, however, serve to show only a small aspect of the 
whole problem. But they illustrate that human progress, 
with respect to biology, is dependent upon our knowledge of 
the intimate life of animals and plants and the general laws 
governing their activities. These have been outlined in the 
previous pages of this book. Let us now select a few concrete 
examples and consider their relation to human progress. 
401. Insect Pests. — Most of us never realized how many 
different kinds of insects there were that feed upon even 
garden vegetables until we tried to do our part by caring for a 
war garden. Nearly all the thousands of plant diseases and 
pests that go to make the life of the farmer, gardener, or 
orchardist unhappy, and greatly to reduce the size or entirely 
destroy his whole crop, a few years ago occupied but small 
territories. So far as our information goes more than one 
half of the insects that cause incalculable losses in our fruits 
and vegetables came from foreign countries. They may 
be said to have migrated to the land of plenty, for in their 
native homes either the amount of food was limited by the 
growing of small crops or their natural enemies were so 
numerous that they were themselves destroyed before they 
could do any marked damage. 
At first thought it seems strange that the government of 
the United States should have a quarantine against insects 
landing at our sea ports, but that is just what the Federal 
Plant Quarantine Act of 1912 means. One department 
of our government is turning its attention to little insects in 
order to save American agriculture by preventing any more 
kinds of insects from, entering the United States. 
402. Fruit-flies.— Some of these insects of other lands that 
are serious pests are popularly known as fruit-flies. They 
