THE UNIQUENESS OF THE INDIVIDUAL 



to the heritage of its young. Lamarckism is a theory that 

 deserves to be taken seriously, and in my Commentary on the 

 subject I have striven to do so. But it is not true; the genetical 

 system of an individual cannot take the impress of the environ- 

 ment; it is a population, not a pedigree, that evolves. Modern 

 Darwinism demands that the genetical system of an individual 

 should be highly stable, as indeed it is. The stability is not 

 absolute, it is true, but departures from it are of a special kind 

 — rare, abrupt and discontinuous; they do not arise in response 

 to an organism''s needs, nor do they, except by accident, gratify 

 them. And even the ''instability' of the genetic mechanism is 

 best thought of as a sudden passage from one stable state to 

 another, for a mutant gene, once it has arisen, perpetuates 

 itself faithfully in its altered form. It is deeply necessary, for 

 any clear understanding of evolution, to distinguish between 

 the genetical structure of a population, which is quite wonder- 

 fully malleable and responsive to the impress of the environ- 

 ment, and the genetical make-up of an individual, which, in a 

 physico-chemical sense, as Schrodinger has told us, is almost 

 miraculously stable. 



One of the most popular misconceptions about the theory of 

 evolution by natural selection is that which treats it as the 

 denouement of the following train of thought: (a) organisms 

 produce offspring in numbers vastly in excess of their needs; 

 {h) only a minority survive; therefore (c) only those survive 

 which are best equipped to do so, the ''fittest\ The catch in 

 this Malthusian syllogism, pointed out years ago by Fisher, 

 lies in its major premise {a). So far from producing a vastly 

 excessive number of offspring, most organisms produce just 

 about that number which is sufficient and necessary to per- 

 petuate their kind. Degree of fecundity is one of the conse- 

 quences of natural selection: it is not its cause. Nidicolous 

 birds, Lack has shown us, illustrate this truth with particular 

 clarity; they do in fact lay clutches of a certain size, though 



14 



