80 



THE RATE OF GROWTH 



[CH. 



see, in short, that the amount of variability in stature or in weight 

 is a function of the rate of growth in these magnitudes, though 

 we are not yet in a position to equate the terms precisely, one witli 

 another. 



If we take not merely the variability of stature or weight at 

 a given age, but the variability of the actual successive increments 

 in each yearly period, we see that this latter coefficient of variability 

 tends to increase steadily, and more and more rapidly, within 



sfi 



o 



Fig. 11. 



Coefficients of variability of stature in Man {^). from Boas 

 and Wissler's data. 



the limits of age for w^hich we have information ; and this pheno- 

 menon is, in the main, easy of explanation. For a great part of 

 the difference, in regard to rate of growth, between one individual 

 and another is a difference of phase, — a difference in the epochs 

 of acceleration and retardation, and finally in the epoch when 

 growth comes to an end. And it follows that the variability of 

 rate will be more and more marked, as we approach and reach 

 the period when some individuals still continue, and others have 

 already ceased, to grow. In the following epitomised table, 



