244 SCIENCE PROGRESS 



alteration must first produce an effect upon the organism as a 

 whole, presumably upon the composition of the body-fluids ; 

 this alteration must act upon the germ-cell so as to change the 

 composition of the cytoplasm ; this change in the cytoplasm 

 must then act upon the complex of hundreds or more probably 

 thousands of genes in such a way that their alteration is trans- 

 formed during development into a somatic alteration similar 

 to the one produced by external agency in the preceding 

 generation. But, owing to the fact that the genes are self- 

 reproducing, and to the further fact that they are only trans- 

 mitted from cell-generation to cell-generation in the form of an 

 aggregate unit, the chromosome-complex, the proportions and 

 locations of whose parts are fixed like those of a complex 

 molecule — owing to these facts, various possible methods of 

 alteration of the gene-complex seem excluded. Alteration 

 of the proportions of its constituent units, the genes, is excluded. 

 Total destruction of one single gene seems excluded ; although 

 its inactivation by some specific lysin or agglutinin is theoreti- 

 cally possible. Change, in fact, seems limited to one of two 

 things. Either some side-chain of a gene can be altered so 

 that the working of the gene, while still similar in essentials, 

 is altered in detail : this process is already known to us in the 

 mutation of single genes, and, so far as at present studied, 

 appears to bear no relation whatever, and certainly not a 

 " Lamarckian " one, to any external stimuli that have been tried. 

 The second is a stimulation of the gene to an over-production 

 of certain substances. In view, however, of the transitory 

 nature of acquired immunity, which must be the prototype 

 of any such changes, and of the fact that it is not transmitted 

 beyond the first generation, and then only through the mother, 

 we must regard this as a speculative possibility only, although 

 one which should by all means be explored. 



In concluding this section, I should like to draw attention 

 to the great similarity subsisting between the present concep- 

 tion and that held by the majority of " Neo-Darwinians." 

 Our knowledge of the mechanism of heredity and of the origin 

 of variations has been enlarged, but the central concept remains 

 unchanged — the concept that the adaptation and the progres- 

 sive evolution of living things, below the human level, has been 

 achieved through a natural selection acting upon variations 

 which are biologically fortuitous. There are some people to 

 whom the idea that chance variations provide the raw material 

 of evolution is unpalatable ; they find in it a contradiction of 

 their ideas on the governance of the universe, and cannot 

 reconcile it with the notion of progress or of any beneficent 

 spirit in cosmic affairs. Such minds have not even reached 

 the stage of the New England lady who was reported to 



