LECTURE VI 

 EVIDENCE FROM EXPERIMENT CONCLUSION 



Experiment is the method used in physics and 

 chemistry, to determine the laws of matter and force; 

 such experiments can be repeated at will and any 

 competent person can obtain the same results. It 

 is highly desirable that the experimental method 

 should be applied in biology, because of the exacti- 

 tude which can thus be secured, affording an in- 

 valuable complement to the results of observation. 

 Darwin always insisted upon the indispensable char- 

 acter of experiments and performed a great many 

 himself. One might have anticipated that the prob- 

 lems of evolution could be thus attacked with suc- 

 cess and subjected to the tests of a precise analysis. 

 But such hopes have left out of account the difficul- 

 ties inherent in the application of the method; human 

 life is very brief and experiments, to be conclu- 

 sive, must often be continued without interruption 

 through a very long series of generations. Then, 

 too, it is impracticable to make conditions in the 

 laboratory sufficiently like those in the open to give 

 definite answers to many questions. 



In a sense, the long continued improvement of 

 domesticated animals and plants by careful breed- 



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