THE DESCENT OF BAD TRAITS AND GOOD. 257 



use has been made by Quetelet, the astronomer-royal 

 of Belgium, the highest authority on vital and social 

 statistics. (See Quetelet, Letters on Probabilities, 

 translated by Downes, London, 1849.) 



The vagrant dots in these equal spaces above and 

 below the line of average follow a law so perfectly, 

 that, frcm knowing one part of the apparently un- 

 symmetrical arrangement, you can draw the map of 

 the rest. If these dots were bullet-marks, they would 

 follow the same law of deviation from an average. 

 Stand yonder with your regiment, and fire your bal- 

 lets against the plank. Aim them all against this 

 central line. Some /will strike below it, some above 

 it, and some will strike the line itself; but when you 

 have determined your average, and the number of 

 bullet-marks in any square, the law of deviation from 

 an average will enable you to estimate with great 

 precision the number of bullet-marks in any other 

 of the squares. 



Now, what has this to do with hereditary descent ? 

 A million men of the same race, brought up here to 

 this measuring-machine, are proved to have heights 

 governed by a fixed law of deviations from an aver- 

 age. It is to be presumed, therefore, that their 

 weight, their muscular strength, the size of their 

 chests and brains, and every one of their physical 

 traits, are governed by a law of averages. But, if a 

 great variety of physical traits may be shown to 

 depend on the law of average in this way, the mental 

 traits may be also. If you can prove that this law 

 uf averages governs the majority of the physical 



