X INTRODUOTION 



the main correct. We may grant very cheerfully that 

 we can attain no demonstration ; the most that we can 

 claim for our results will be a high degree of proba- 

 bility. If our conclusions are very probably correct, 

 we shall do well to act according to them; for all our 

 actions in life are suited to meet the emergencies of a 

 probable but uncertain course of events. 



We take for granted the probable truth of the theory 

 of evolution as stated by Mr. Darwin, and that it ap- 

 plies to man as really as to any lower animal. At the 

 same time it concerns our argument but little whether 

 natural selection is " omnipotent " or of only secondary 

 importance in evolution, as long as it is a real factor, 

 or which theory of heredity or variation is the more 

 probable. 



If man has been evolved from simple living sub- 

 stance protoplasm, by a process of evolution, it will 

 some day be possible to write a history of that process. 

 But have we yet sufficient knowledge to justify such 

 an attempt? 



Before the history of any period can be written its 

 events must have been accurately chronicled. Biolog- 

 ical history can be written only when the successive 

 stages of development and the attainments of each 

 stage have been clearly perceived. In other words, 

 the first prerequisite would seem to be a genealogical * 

 tree of the animal kingdom. The means of tracing 

 this genealogical tree are given in the first chapter, 

 and the results in the second, third, and fourth chap- 

 ters of this book. 



Now, for some of the ancestral stages of man's de- 

 velopment a very high degree of probability can be 



* See Phylogenetio Chart, p. 310. 



