72 Variation 



knows that Darwin was always very careful in statements of this 

 kind. 



From the same chapter I may here cite the following paragraph : 

 "Tims as I am inclined to believe, morphological differences,... 

 such as the arrangement of the leaves, the divisions of the flower or 

 of the ovarium, the position of the ovules, etc. — first appeared in 

 many cases as fluctuating variations, >vhich sooner or later became 

 constant through the nature of the organism and of the surrounding 

 conditions. . .but not through nattiral selection^', for as these morpho- 

 logical characters do not afl'ect the welfare of the species, any slight 

 deviation in them could not have been governed or accumulated 

 through this latter agency^." We thus see that in Darwin's opinion, 

 all small variations had not the same importance. In favourable 

 circumstances some could become constant, but others could not. 



Since the appearance of the fii'st edition of The Origin of Species 

 fluctuating variability has been thoroughly studied by Quetelet. He 

 discovered the law, which governs all phenomena of organic life 

 falling under this head. It is a very simple law, and states that 

 individual variations follow the laws of probabilitj'. He proved it, 

 in the first place, for the size of the human body, using the measure- 

 ments published for Belgian recruits ; he then extended it to various 

 other measurements of parts of the body, and finally concluded 

 that it must be of universal validity for all organic beings. It must 

 hold true for all characters in man, physical as w^ell as intellectual 

 and moral qualities; it must hold true for the plant kingdom as 

 well as for the animal kingdom ; in short, it must include the whole 

 living world. 



Quetelet's law may be most easily studied in those cases where 

 the variability relates to measure, number and weight, and a vast 

 number of facts have since confirmed its exactness and its validity 

 for all kinds of organisms, organs and qualities. But if we examine 

 it more closely, we find that it includes just those minute variations, 

 which, as Darwin repeatedly pointed out, have often no significance 

 for the origin of species. In the phenomena, described by Quetelet's 

 law notliing "happens to arise"; all is governed by the common 

 law, which states that small deviations from the mean type are 

 frequent, but that larger aberrations are rare, the rarer as they are 

 larger. Any degree of variation will be found to occur, if only the 

 number of individuals studied is large enough: it is even possible 

 to calculate beforehand, how many specimens must be compared in 

 order to find a previously fixed degree of deviation. 



The variations, wliich from time to time happen to appear, are 

 evidently not governed by this law. They cannot, as yet, be pro- 



» The italics are mine (II. de V.). » Origin of Species (6th edit.), p. 176. 



