THE UNIQUENESS OF THE INDIVIDUAL 



may sometimes be the only way in which eUmination can be 

 achieved; but I cannot argue this without an appeal to the 

 phenomena of pleiotropy and hnkage, which time Avill not 

 allow. 



VIII 



It is not good enough to say that what happens to very old 

 animals hardly matters and that what happens to youngsters 

 matters a great deal. For the degree to which anything may 

 matter varies in a predictable way with age, and the selective 

 advantage or disadvantage of a hereditary factor is rather 

 exactly weighted by the age in life at which it first becomes 

 eligible for selection. A relatively small advantage conferred 

 early in the life of an individual may outweigh a catastrophic 

 disadvantage withheld until later.^ Go back to the test-tube 

 model for a moment, and compare two competing test-tube 

 populations. Both suffer the same average monthly mortality 

 of 10 per cent., and one has, as hitherto, the average monthly 

 birth-rate of 10 per cent. The other population has an average 

 monthly birth-rate of 11 per cent., but the price paid for this 

 hardly profligate increase of fecundity is the spontaneous 

 bursting asunder of each member at age two. Which population 

 will increase the more rapidly in numbers — that potentially 

 immortal, or the mortal population with a birth-rate only 



the time of action of a gene G with respect to a character Cis the age at which, 

 in a stated genetic and environmental context, the substitution of G for its 

 allelomorph G' transforms the character C into the character C. In short, 

 it doesn't matter when (or even whether) G and G' are 'acting' until they 

 give evidence of acting in different ways. 



^ By something that is a catastrophic disadvantage to an older animal 

 I mean a change which is personally catastrophic, and which would 

 certainly be catastrophic to the species as well if it made its appearance in 

 younger animals. But in the strict sense, the verdicts 'advantageous' and 

 'disadvantageous' can be delivered only after trial by selection, and in this 

 sense to speak of 'catastrophic disadvantages' which don't in fact much 

 matter is self-contradictory. 



64 



