THE ARGUMENT FROM DISEASE 165 



progressive and regressive, is founded on variations in individ- 

 uals ; and it is popularly believed that variations in individuals 

 are caused or at any rate influenced by external agencies 

 acting on the germ-plasm. 



280. In the present state of our knowledge every theory of 

 heredity which rightly aspires to be anything more than a 

 mere working hypothesis is in effect a theory of the origin 

 of variations. And every theory which seeks to account for 

 variations has, as a necessary corollary, a theory of racial 

 change. Setting aside miracle, there are only two ways 

 possible of accounting for variations. First, we have the 

 supposition that variations arise through the action of the 

 environment on the germ-plasm, secondly, we have the sup- 

 position that variations arise spontaneously. 1 To me at 

 least the theory of spontaneous variations does not imply 

 mere " blind chance." It implies that variations arise through 

 the action of a highly advantageous tendency to vary in all 

 directions about the specific mean, which was evolved very 

 early in the history of all life by Natural Selection, and which 

 was a necessary antecedent to all other evolution. 2 The 

 Lamarckian doctrine is no more than a particular application 



assisted by the strong. Nevertheless disease takes its toll and eliminates 

 large numbers. But suppose a race existed in which every form of 

 elimination except death from old age were suddenly abolished, so that 

 even the weakest individuals had their full quota of offspring ; then, in 

 the fulness of time, the race would infallibly press on its food supply 

 to such an extent as to check its increase. The survival of the fittest 

 would again obtain ; and under such conditions (i. e. if there were no 

 struggle an actually impossible condition) the fittest would be the 

 smallest, the least complex, the most degenerate individuals the 

 individuals that required the least food. 



1 Weismann's hypothesis ingeniously combines both these hypotheses. 

 He believes that variations are caused in the first instance by influences 

 from the environment, but that they are subsequently shuffled and 

 re-shuffled during the repeated acts of sexual reproduction. They are 

 thus presented to nature for selection in the guise of spontaneous 

 variations. 



2 To state the case in brief terms : If variations are caused by exter- 

 nal influences, then, though we are able to account for the variations of 

 individuals, yet the species is evidently exposed to blind chance. It 

 deteriorates helplessly under adverse influences. But if variations arise 

 spontaneously, then, though the individual is exposed to blind chance, 

 the species is not. Moulded by Natural Selection it meets every change 

 in the environment, beneficial or adverse, with an appropriate reaction. 

 Under the first hypothesis the evolution and persistence of species is 

 inexplicable. Under the second we are able to understand how species 

 not only persist, but, as a condition of persistence, adjust themselves 

 with the greatest nicety to every change in the environment. 



