tradition: the evidence of biology 



ceed from the groundwork of what has been achieved before. 

 Failure, abortion or extinction occur as commonly in the one 

 as in the other; 'vestigial organs'*, like the coccyx or appendix, 

 or those functionless buttons on the cuffs of men"'s coats, occur 

 in both. Whether or not you choose to describe the systematic 

 secular change of exosomatic instruments as an ''evolution'' is 

 utterly unimportant; all I am concerned to emphasize is that 

 both exosomatic and endosomatic ''evolution'' are equally 

 modes of the activity of living things, and that both are 

 agencies — to some extent alternative agencies — for increasing 

 biological fitness, i.e. for increasing those endowments which 

 enable organisms to sustain themselves in and prevail over 

 their environments. In man, ordinary evolution as we under- 

 stand it in lower animals, endosomatic evolution, does still 

 happen, and I could give examples of evolutionary changes 

 that have occurred within the known history of the human 

 race. But they are changes of a comparatively minor character, 

 whereas the changes wrought upon human society by exo- 

 somatic evolution have been rapid and profound. 



I now at last come to the point. There is one crucial dis- 

 tinction between endosomatic and exosomatic evolution. 

 Ordinary evolution is mediated by the process of heredity. 

 Exosomatic ''evolution'' (we can still call it ''systematic secular 

 change'') is mediated not by heredity but by traditio7i, by 

 which I mean the transfer of information through non-genetic 

 channels from one generation to the next. So here is a funda- 

 mental distinction between the Springs of Action in mice and 

 men. Mice have no traditions — or at most verv few, and of a 

 kind that would not interest you. Mice can be propagated from 

 generation to generation, with no loss or alteration of their 

 mouse-like ways, by individuals which have been isolated from 

 their parental generation from the moment of their birth. But 

 the entire structure of human society as we know it would be 

 destroyed in a single generation if anything of the kind were 



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