E\'OLmON .A^ A NATTR-^L PROCESS 121 



which might not be represented among one thousand 

 people. 



It is not possible to explain why variation dioiikl 

 follow this or any other mathematical law without 

 entering into an unduly extensive discussion of *^- 

 laws of error. The mathematicians themselves leli 

 us in general terms that the observations they describe 

 so simply by their formulff : v as the result of 

 so-called chance, by which theyme-an that the combined 

 operation of numerous, diverse, and uncorrelated factors 

 brings about this result, and not, of course, that there 

 is such a thing as an uncaused event or phenomepon 



Whenever any extensive series of like oreani^^ms has 



been studied with reference to the var„. s of a 



particular character, the variations group themselves so 

 as to be described by identical or similar cun-es of error. 

 It is certainly significant that this is true for such 

 diverse characters, cited at random from the lists of 

 the Hterature, as the nimiber of ray-flowers of white 

 daisies, the ntunber of ribs of beech leaves, and of the 

 bands upon the capsules of poppies, for the shades of 

 color of human eyes, for the nimiber of spines on the 

 backs of sJirimps, and for the number of da\^ 

 caterpillars feed before they turn into pupae. 



To summarize the foregoing facts^ we have learned 

 that variation is univeTsal throu^out the hving worid, 

 and that the primar>' factors causing orcanic dif- 

 ference — the coimterparts of human i: - in 

 the ca,se of dead mechanisms — are the in- 

 fluences of the en\'ironment, of organic physic ..« — 

 activity, and of congenital inheritance. These factors 

 are accorded different values in the eve ' a of new 



