50 MAN ON THE LANDSCAPE 



Imbedded in some of these rocks he found signs of once living plants 

 and animals. 



These fossils gave rise to the science of paleontology, which in turn 

 has shed much light on the evolution of life forms. The paleontologist 

 found that as the landscape changed in pre-historic times, life changed 

 too. Not only that, but life itself effected changes in the landscape, 

 particularly in the soils. It was, and is, a reciprocal, interacting re- 

 lationship. Also significant in bringing about changes were climatic 

 shifts (notably the coming and going of the several ice sheets), the 

 uplift of mountain ranges which changed wind effects and precipita- 

 tion patterns, and the shifting relationships of land and water masses 

 which altered weather factors. (The Great Lakes, for instance, so 

 affect climate that many fruits grow as well to the southeast of those 

 waters as they do in southern Tennessee. ) 



As a result of such changes we find semi-arid land now covering 

 coal which could only have been produced in a swamp, oyster shells in 

 Wyoming, sand of ancient seashores in the Appalachian Plateau, 

 limestone formed from sea animals in the present prairie states. 



All through the record of the rocks, life was either adjusted by 

 means of hybridization or mutations to the changes in environment, 

 migrated and found another suitable environment, or became extinct. 

 There are enough examples of such adaptation to prove that life in 

 many instances was adjusted to altering conditions. 



One explanation of how it did this was exploded in the face of a 

 "fundamentalist" world by Darwin. His observations, which anyone 

 can verify, were that no two organisms, of the same species, or even 

 sub-species, are exactly alike. These variations range from almost un- 

 detectable differences up to marked deviations from the normal. Later 

 studies by other botanists uncovered rather rare but unmistakable 

 cases of radical variations variations so extreme that they were 

 called mutations, or sports. 



Darwin's work (Wallace was on the same trail at the same time 3 ) 

 led him to conclude that in a changing environment, certain of the 

 ordinary, chance variations would be better able than others to survive 

 such changes in habitat. Some of these survivors would reproduce the 

 new characteristics and so establish new species. This interpretation 

 became known as the theory of evolution by natural selection. 



The later studies of mutations, pioneered by DeVries, bolstered the 

 theories of Darwin and Wallace. It was found that remarkable varia- 

 tions and mutations could be caused by unusual temperatures, in- 

 juries, certain chemicals, X-rays and other irradations (which in 

 nature might arise from radio-active minerals, cosmic rays, or ultra- 

 violet and infra-red rays). It should be noted that many, even most of 

 these changes in offspring have no relation to survival. They occur 

 constantly; and if environment changes, there may accidentally ap- 



3 Norden Skold, Erik, History of Biology, Alfred Knopf, New York, 1928. 

 Part III, pp. 485-88. 



