AN UNSOLVED PROBLEM OF BIOLOGY 



one-tenth part higher than the other's? The simplest calcula- 

 tions show that it is the latter. 



A heightened juvenile rate of reproduction, achieved perhaps 

 at the expense of recurrent stress that later leads to deteriora- 

 tion, is by no means the only possible realization of the 

 phenomenon illustrated by this model. It is a general rule, for 

 example, that the parts of the body multiply their substance at 

 unequal rates, so that proportions change as the body grows. 

 There is very likely to be a ""best"* proportion, or a best range of 

 proportions, from the standpoint of functional efficiency and 

 therefore of survival. In theory these proportions could be 

 arrived at once and for all by starting the baby or embryo off 

 with the appropriate shape and allowing growth to proceed by 

 symmetrical enlargement. This does not happen in practice, 

 and it is not biologically feasible for a whole variety of reasons. 

 In practice, as I have already said, adult proportions are 

 achieved by the adoption of a more or less fixed regimen of 

 differential growth, i.e. of a more or less constant ratio between 

 the multiplication rates of the several parts of the body. The 

 danger inherent in this alternative solution is that there may 

 well come a size, and therefore an age, at which proportions 

 become functionally and structurally grotesque. The size of the 

 male fiddler crab''s claw increases as a power, greater than 

 unity, of the size of the rest of its body, and Dr Huxley, who 

 has made a special study of these differential growth pheno- 

 mena, points out that a crab whose body weighed 1 kg. would 

 carry a claw about ten times that weight. But the sense of my 

 argument is that if the appropriate proportions are achieved 

 at some earlier stage of life, it may not much matter that the 

 regimen of differential growth that brought them into being 

 should eventually lead to mechanical ineptitude of this degree. 

 The early advantage more than makes good the later dis- 

 advantage which it necessarily entails. 



E 65 



