LECTURE II 



EVIDENCES FOR THE THEORY— CLASSIFICATION, 

 DOMESTICATION AND COMPARATIVE ANATOMY 



Before attempting to set before you an outline 

 sketch of the evidence which has so firmly convinced 

 zoologists and botanists that the theory of evolution 

 is true, it is necessary to begin with a warning not to 

 expect too much; that is to say, more complete proof 

 than, in the nature of things, it is possible to obtain. 

 Evolution has been a long, historical process, which 

 has gone on with extreme slowness through un- 

 imaginable ages of time, when no man was there to 

 see and observe. Complete demonstration, such as 

 may be given for a physical or chemical law, is there- 

 fore not to be expected. Even in so exact a science 

 as astronomy, the attempt to work out historical 

 problems is beset with the gravest difficulties. No 

 astronomer, for example, doubts that the solar sys- 

 tem is a unit, which has been developed from some 

 originally continuous body of matter, such as a 

 nebula, but there is no general agreement as to the 

 manner in which this development was brought 

 about. Any solution yet proposed is face to face 

 with unsolved problems. Clearly, therefore, the 

 evidence for organic evolution must be indirect, since 

 direct proof is unattainable, yet it need not be un- 



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