402 General Biology 



series. All conclusions built upon these finds must, therefore, be purely 

 conjectural. 



From the evidence presented here, we note the fact that many pres- 

 ent-day forms of both plants and animals are unlike their ancestors. 

 We are, therefore, confronted with four possible explanations of why 

 they are different: (1) that present-day forms are the lineal descendants 

 of ancestral forms unlike themselves and that all new forms with ever 

 increasing complexity spring from older ones ; (2) that new forms dif- 

 ferent from the older ones have been created at different periods; (3) 

 that all forms were brought into existence at about the same time, but 

 due to a great world upheaval the fossiliferous strata have been so 

 confusedly arranged that, while all fossils are of one age, it is our 

 mistaken interpretation which makes us believe they are of different 

 ages ; or (4) that organisms came into existence which, at the time of 

 their origin, had the possibility of change placed within their germ- 

 plasm, but which had to await the proper conditions of food and environ- 

 ment before they could come forth to produce present-day forms. 



If it be accepted that any present-day forms are different from their 

 ancestors, and that these new forms can produce offspring capable of 

 transmitting that change to their posterity in turn, we must speak of an 

 evolution as having taken place. 



References. 



Karl von Zittel's "History of Geology and Paleontology." 



A. Dendy, "Outlines of Evolutionary Biology." 



H. A. Nicholson, "Manual of Paleontology." 



Charles Schuchert, "Historical Geology." 



A. Morley Davies, "An Introduction to Paleontology." 



H. S. Williams, "Geological Biology." 



Articles on Geology, Paleontology, etc., in Encyclopedia Britannica. 



