There is no conclusive evidence that modifications arising in an individ- 

 ual's Ufetime are transmitted to the offspring. 



The theory that species originated through natural selection rests on the 

 facts (1) more individuals are produced in each species than can possibly ma- 

 ture and reproduce, and (2) individuals in a species vary among themselves. 

 The theory rests upon the suppositions (1) in the "struggle for existence" 

 which ensues from the pressure of population only the "fittest" survive, and 

 (2) the survivors transmit their advantageous characteristics to their offspring. 



The theory of natural selection (1) overlooks destructive conditions that 

 are in no sense "selective", (2) disregards the apparent modifications that are 

 not adaptive, and (3) fails to distinguish clearly between variations that are 

 inherited and those that are not. 



EXPLORATIONS AND PROJECTS 



1 To make a collection of fossils, visit exposed beds of sedimentary rock; 

 split open pieces of limestone or shale, or concretions found in coal or shale 

 deposits, in search of imprints or remains of living things which may be con- 

 sidered as fossils. Identify and label specimens, recording place where found, date, 

 kind of rock in which found, name of fossil, and the geological era or period in 

 which it probably was formed. 



2 To become acquainted with life forms characteristic of Paleozoic, Mesozoic, 

 and Cenozoic times, visit a natural-history museum and study the types of life 

 dominant in each era. 



3 To estimate the reproductive possibilities in a single plant, collect the seed- 

 stalk and count the number of seeds. Select a plant which easily becomes a weed 

 pest, such as dock or ragweed, or a plant commonly raised for food, such as corn 

 or wheat or radish. Estimate how many plants could be produced in three or 

 four seasons if each seed grew and each successive plant produced the same 

 number of seeds. 



QUESTIONS 



1 Why do not all observers of the same facts come to the same conclusions? 



2 What assumptions do you prefer to make as a basis for interpreting the 

 past history of the world.'' Why do you select these assumptions rather than 

 others ? 



3 What are fossils? Where do we find them? In what different ways are 

 they preserved? 



4 If we accept fossils as representing past life upon the earth, what do the 

 actual fossils and their distribution suggest about the history of life on the earth? 

 What changes do they suggest in the earth itself? 



5 What likenesses and differences do we find among the various mammals ? 

 among all vertebrates? 



470 



