GROWTH 



293 



methods would be useful if they were applied. The changing shape 

 of animals as they mature is of practical importance in relation to the 

 production of hvestock. Hammond (1950) has been particularly con- 

 cerned with the problem and has demonstrated a number of general 

 points about the physiology of growth gradients. These he has been able 

 to illustrate pictorially, but it has so far not been easy to reduce them to a 

 precise and manageable form; Medawar's methods might be very useful 

 in this connection. 



2575 Years 



Figure 13.5 



Changes in the proportions of the human body during growth. The heights 

 of certain landmarks (knees, fork, navel, mouth, etc.) were ascertained for 

 each age, and related to one another by means of empirical equations. From 

 these equations the heights were recalculated, to give the horizontal lines 

 which are drawn on the figures. The goodness of fit of these lines indicates 

 the degree to which the changes in proportions have occurred in a regularly 

 graded manner, so as to lend themselves to summarising in relatively simple 

 algebraic functions. (From Medawar 1945.) 



Hammond shows that the various species of wild animals from wliich 

 our domestic livestock have been derived have each their characteristic 

 pattern of changes in shape during development. These can be illustrated 

 rather vividly if one takes as a standard an early developing part such as 

 the head and shows a series of drawings or photographs of different stages 

 of the animal, all of which have been adjusted to the same head size. 

 We then see that in the horse, for instance (Fig. 13.6), up to the time 



