The Making of Species 



of development along disadvantageous lines, or 

 to disadvantageous degrees. The statistical 

 studies of variation have made known numerous 

 cases where the slight, as yet non-significant (in 

 a life-and-death struggle) variation in pattern of 

 insects, in dimensions of parts, in relative pro- 

 portions of superficial non-active areas, are not 

 fortuitous, that is, do not occur scattered evenly 

 about a mean or mode according to the law of 

 error, but show an obvious and consistent tendency 

 to occur along certain lines, to accumulate in 

 certain directions." 



It seems to us that the only proper attitude to 

 adopt in the present state of our knowledge is, 

 not to call in to our aid an unknown growth- 

 force, but simply to say that there is evidence 

 to show that variations frequently occur along 

 certain definite lines only. 



Darwin's second assumption was that there is 

 no limit to which variations may be accumulated 

 in any direction ; that by adding one minute 

 variation to another through countless generations 

 new species, new genera, new families may arise. 

 This assumption, if applied to continuous or 

 fluctuating variations, seems opposed to facts. 

 All the evidence available goes to show that 

 there is a definite limit to which minute variations 

 can be accumulated in any given direction. No 

 one has succeeded in breeding a dog as large as 

 a horse, or a pigeon with a beak as long as that 



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