190 THE ORIGIN OF SPECIES 



CHAPTER V 



LAWS OF VARIATION 



Effects of changed conditions — Use and disuse, combined with natural 

 selection ; organs of flight and of vision — Acclimatization — Correlated 

 Variation — Compensation and economy of growth — False correlations 

 — Multiple, rudimentary, and lowly organized structures variable — 

 Parts developed in an unusual manner are highly variable: specitic 

 characters more variable than generic: secondary sexual characters 

 variable — Species of the same genus vary in an analogous luanner — 

 Reversions to long-lost characters — Summary 



I HAVE hitherto sometimes spoken as if the variations 

 — so common and multiform with organic beings 

 under domestication, and in a lesser degree with 

 those under nature — were due to chance. This, of 

 course, is a wholly incorrect expression, but it serves to 

 acknowledge plainly our ignorance of the cause of each 

 particular variation. Some authors believe it to be as 

 much the function of the reproductive system to produce 

 individual differences, or slight deviations of structure, 

 as to make the child like its parents. But the fact 

 of variations and monstrosities occurring much more fre- 

 quently under domestication than under nature, and the 

 greater variability of species having wide ranges than of 

 those with restricted ranges, lead to the conclusion that 

 variability is generally related to the conditions of life 

 to which each species has been exposed during several 

 successive generations. In the first chapter I attempted 

 to show that changed conditions act in two ways, directly 



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