CHANGES IN ENVIRONMENT 



21 



Changes in Environment. — Most plants and animals do not 

 change their environment. Trees, green plants of all kinds, and 

 some animals remain fixed in one spot practically all their hves. 

 Certain tiny plants and most animals move from place to place, 

 either in air, in water, on the earth or in the earth, but they main- 

 tain relatively the same conditions in environment. A high moun- 

 tain chain with intense cold at the upper altitudes would be a barrier 

 over which, for example, 

 a soft-bodied animal like 

 a worm or a snail could 

 not travel. Certain 

 species of trout are found 

 on the western side of the 

 continental divide and 

 other species on the 

 eastern side. Fish will 

 migrate up a stream until 

 they come to a fall too 

 high for them to jump. 

 There they must stop be- 

 cause their environment 

 limits them. 



Man in his Environ- 

 ment. — Man, while he 

 is like other animals in 

 requiring heat, light, 

 water, and food, differs 

 from them in that he has 

 come to live in a more 

 or less artificial environ- 

 ment. Men who lived on the earth thousands of years ago did 

 not wear clothes or have elaborate homes of wood, brick, or 

 stone. They did not use fire, nor did they eat cooked foods. In 

 short, by slow degrees, civilized man has come to live in an en- 

 vironment changed from that of other animals. He has learned 

 to build houses and to use fire. The living together of men in 

 communities has caused certain needs to develop. Many things 

 can be supplied in common, as water, milk, and fuel. Wastes 



H. NSW CIV. BIOL. — 3 



An unfavorable city environment. Compare 

 with the favorable city environment shown in 

 the frontispiece. 



