GAUSS'S LAW OF FREQUENCY 99 



allow of variations. Such organisms are generally far more 

 long-lived, and although they do not produce such a number 

 of young at a time, still, as they go on producing young for 

 a greater number of years, a simple calculation will show 

 that if all the offspring survived and bred in their turn, the 

 world would, in a very few years, be overwhelmed by the 

 organism in question. 



Small variations occur in every direction round the 

 mean of every character. It has been shown that Gauss's 

 law of frequency of error applies to variations. 1 Sir John 

 Herschel's illustrations of this law makes its application very 

 clear. 2 He pointed out that if a large number of shots were 

 tired by a rifleman at a target, the shots aggregated most 

 thickly round a particular point, and became fewer in propor- 

 tion to the distance from this point. The area of the closely 

 collected shot-marks varies according to the skill of the 

 marksman. The greater the skill, the smaller will the area 

 be in which the greater number of the shots are found. 

 Precisely the same thing happens in the case of variations. 

 With regard to some characters, the vast majority of varia- 

 tions are generally very small, while with regard to others, 

 more considerable variations may be comparatively common. 

 The probability is that those characters upon which selection 

 has acted most stringently for the longest period of time, 

 will be those which show the smallest variations. When, 

 however, we go to the opposite extreme, and consider charac- 

 ters that have been rapidly produced by artificial selection, 

 we find more considerable variations exceedingly common. 



We have, then, apparently ample material in the way 

 of variations to account for the production of new characters 

 under the action of natural selection. 



Formerly a comparatively limited time was allowed for 



1 Quetelet, Lettres & S.A.R. le Due regnant de Saxe-Cobourg et Gotha sur la 

 Theorie des Probabilites appliquee aux Sciences Morals et Politiques, Brussels, 

 1846 ; Galton, Inquiries into Human Faculty (Everyman's Library Edition), 

 pp. 33 ct scq. 



2 Edinburgh Review, 1850. 



