18 BIOLOGY 



appearance for the first time. In an early period of the world's 

 history, the earth was a hot, molten mass, and under these 

 conditions no living matter could exist. It follows, then, that 

 life must have made its appearance after the earth had suffi- 

 ciently cooled. Biology, in endeavoring to explain life by 

 natural forces, has been eager to believe that in these earlier 

 conditions of the world the first living thing may have ap- 

 peared as the result of natural law. The fact that biologists 

 have almost universally accepted Tyndall's conclusion that 

 no evidence for spontaneous generation exists, is thus a testi- 

 mony, both to the truth of this conclusion and to the honesty 

 of the scientists who have accepted it. They would have much 

 preferred a conclusion of the opposite kind. The majority of 

 biologists, however, believe it to be logically necessary to as- 

 sume that at some time in prehistoric ages, the first living 

 thing appeared from a source which was not living. While 

 accepting the fact that abiogenesis does not occur at the present 

 day or under present conditions, biologists still claim that we 

 have no means of knowing what may have occurred under 

 different conditions in earlier eras of the world's history. Thus, 

 the problem of the primal origin of living matter still remains 

 unsolved. 



THE BIOLOGICAL SCIENCES 



Since the science of biology deals with all living matter, it 

 might broadly be defined as the study of life in all its phases. 

 With this comprehensive definition, biology can be made to 

 cover nearly the whole field of human knowledge most sciences 

 and even philosophy including not only everything which 

 relates to the life of man, but all that concerns the life of the 

 animal and plant world as well. But for practical convenience 

 in study, the field of biology is usually restricted to a group of 

 definitely related sciences, the so-called biological sciences, 

 and although within this group there are to be found many 

 ill-defined boundary lines, and much overlapping and division 



