DARWINISM AND HEREDITY. 33 



it is the definition of the word fittest from the point of 

 view of the scientific observer. When one organism is 

 said to be more or less fit than another, no aspersion is 

 cast on the moral worth or aesthetic beauty of either 

 from a purely human standpoint ; but the fact is ex- 

 pressed that in the environment in which they live, one 

 will succeed and the other fail. So when we speak of 

 higher and lower forms in evolutionary series, we have 

 , no desire to made invidious distinctions, but take into 

 account the fact that some organisms are more complex 

 and elaborate in their structure, bodily and mental, than 

 others. 



According to Darwin, the chief factors which contrib- 

 ute to the process of evolution are, variation, heredity, 

 and the struggle for existence/ He pointed out that man 

 has modified the characters (bodily and mental structure) 

 of domestic animals and plants by continually selecting 

 and breeding from those individuals which varied in 

 directions favourable to his purpose, and gave the name 

 natural selection to the similar process going on in nature. 

 While the doctrine of evolution has been universally 

 accepted, there is still much difference of opinion as to the 

 relative importance of the various factors concerned. 



The impetus given by Darwin to the study of biology 

 was enormous, especially with regard to variation and 

 heredity, subjects which before his time had received 

 little serious attention. We must now examine more in 

 detail these factors of evolution. 



However closely related organisms may be, they always 

 differ from each other : parents and offspring, brothers 

 and sisters are never quite alike. The differences between 

 them are called variations. Familiar to us among forms 

 which we know well and observe closely, as for instance 

 individuals of the human species, or our domestic animals 

 and plants, variation is no less universally present among 

 all sorts of living organisms. Variability occurs in vari- 

 ous degrees, in all possible directions, and extends to 



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