EVOLUTION 2 5 I 



come increasingly difficult, and finally end. We have since learned that 

 glaciers are no new thing in the earth's history. There was extensive glacia- 

 tion at sea-level in India, South Africa and South America at the end of 

 the Paleozoic, perhaps two hundred million years ago. Another extensive 

 glaciation occurred twice as far back, before the beginning of the Paleo- 

 zoic. Climatic changes seem to have been rhythmic instead of progressive; 

 swings from warm to cold, and back again; from wet to dry and dry to 

 wet; but at all times of a character to permit human life, had it been in 

 existence. There is no reason to suppose that conditions will not continue 

 much the same in time to come. The weather prediction for the future is 

 "favorable." Today's climate, like all weather everywhere, is "exceptional." 

 We are still in the fag end of a glacial period, with immense ice-sheets in 

 Greenland and Antarctica, and abundant mountain glaciation. There have 

 been four generations in the Pleistocene. It is quite within the realm of 

 the possible that another ice sheet may develop in Canada, push south into 

 the United States, and overwhelm New York, Cleveland and Chicago; the 

 last ice sheet reached that far. The next, if there is a next, may do the same. 

 It will not be a glacial blitzkrieg, however. There will be plenty of notice 

 in advance. And it will be exceptional. Through most of the past the 

 climate has been mild and uniform, and it will probably be so through most 

 of the future. 



The environmental aspects just mentioned are exempt from interference 

 on the part of man. Others are not. Man cuts the forest, plows the grass- 

 lands, and plants his corn and wheat. He digs or drills the ground for his 

 fuels and his metals. These are his resources for food, for industry. How 

 is it faring with these natural resources? 



First, as to the food supply. There will be enough to eat, if . . . There 

 have been times in the past when a land animal hke man would not have 

 found enough to eat, enough of the right kinds of food. When the lung 

 fish of Devonian times came ashore to become the ancestor of vertebrate 

 land hfe, he found an abundant vegetation. But it did not contain our 

 present foods. None of the plants which fill the spring seed catalogues 

 were then in existence. Flowering plants did not come until late in the 

 Mesozoic, nor were grasses and grains, man's basic foods, abundant until 

 the Cenozoic. But now they are with us. Nature has done her part. "Be- 

 hold I have given you every herb yielding seed, which is upon the face of 

 the earth, and every tree, in which is the fruit of a tree, yielding seed; to 

 you it shall be for food." What man is doing at improving this endow- 

 ment is told in the splendid story of modern scientific agriculture. 



But plants require soils; aye, there's the rub! We are waking to the fact 

 that soils are being destroyed in this country at an alarming rate. They 

 are being washed to sea by the rivers and blown away by the winds. Al- 

 ready from one quarter to all of the top soil has been eroded from 59 per 

 cent, of the United States. They are being impoverished by cropping with- 



