PART I- -VARIATION 



CHAPTER I 



VARIATION IN GENERAL 



SECTION I VARIATION UNIVERSAL AMONG LIVING 



BEINGS 



The most obvious fact about living beings is their variability. 

 Not only do species differ from each other by many and widely 

 different characters, but individuals within the species are distin- 

 guished by differences readily discernible, at least by the trained 

 observer. The general differences between horses and cattle, for 

 example, are specific and distinct and therefore striking even to 

 the casual observer ; but to the trained eye all horses are not 

 alike, and so it is that differences are detected within the species. 

 Two individuals may be recognized as possessing the same char- 

 acters and therefore related by descent, but invariably these 

 characters differ in degree or in their proportions one to another. 



Two animals may be of the same or of different colors, but in 

 either event the parts are differently proportioned. The leg of 

 one is longer, larger, or more crooked than that of the other. 

 The bones composing the two are not of equal, or even of pro- 

 portional, lengths. Two cows of the same breed differ marvel- 

 ously in the amount of milk they can yield in a year, and some 

 are known to produce three times as much butter fat as others 

 from the same amount of the same kind of feed. 1 Again, some 

 milk is rich in fat (6 or even 8 per cent) while other is poor 

 (2 per cent or even less). Some horses, because of their con- 

 formation, travel more easily or more rapidly than others, and 

 some are more intelligent or more enduring or more docile. 



1 See data from Agricultural Experiment Station, University of Illinois. 



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