152 OUTLINES OF EVOLUTIONARY BIOLOGY 



imperfection is undoubtedly due in the main to the fact that the 

 number of observations upon which it is based has not been 

 sufficiently large to give a fair average. 



The larger the number of individual cases examined and 

 recorded the more closely will our zig-zag line approximate to 

 a regular curve. Even as it is, with all its imperfections, it 

 shows certain very characteristic features. It rises steeply 

 in the middle and falls away from the highest point, at first 

 suddenly and then more gradually, on either side. This is a 

 graphic representation of the facts, (1) that the most frequently 

 occurring number of flowers in the inflorescence (28) lies not very 

 far from midway between the two extremes, and (2) that the 



Stature fn Inche 



FlG. 73. Fluctuating Variation in Human Stature. (From Lock.) 



more the number of flowers deviates from this mean on either 

 side the smaller is the corresponding number of inflorescences ; 

 or, to put it more generally, the number of individuals exhibiting 

 any given degree of deviation from the mean condition of the 

 species is inversely proportional to the amount of that 

 deviation. 



Fig. 73 is a diagram constructed on the same principles as 

 the above, but based upon totally different material and a very 

 much larger number of observations. It is taken from Mr. R. H. 

 Lock's work on " Variation, Heredity and Evolution," and shows 

 the variation in stature observed amongst 4,426 British members 

 of the University of Cambridge. The dots in this diagram 

 correspond to the middle points of the tops of the vertical columns 

 in the preceding one. The statures are reckoned in the nearest 



