466 HEREDITY AND DEVELOPMENT 



indeed, the old method of the philosophisers of nature. . . . 

 The worst feature of the situation is not so much that Weismann 

 has advanced new hypotheses unsupported by experimental 

 evidence, but that the speculation is of such a kind that it is, 

 from its very nature, unverifiable, and therefore useless." 



These are hard words, but it would have been more to the 

 point to inquire whether Weismann's imaginative picture of 

 what may go on within the microcosm of the germ-plasm is in 

 any way contradictory of known biological results. Of course, 

 the theory is " unsupported by experimental evidence," and 

 " removed from the field of verification " ; but why it is therefore 

 " useless " we fail to see. It appears to us quite on the same 

 plane as many symbolic interpretations in chemistry and physics, 

 where we say that if we picture atoms and molecules, electrons 

 and corpuscles, in such and such a way, then we can redescribe 

 more clearly the observable sequences of conditions and results, 

 and devise further experiments which will test the adequacy 

 of our symbols and enable us to improve them. The struggle 

 of determinants may not be quite as Weismann supposes, but 

 the idea is a logical extension of the selective process which 

 occurs at many different levels ; it clarifies our picture 

 of observable facts, and it stimulates further inquiry. 



Summary. Convinced that the theory of natural selection 

 in the Darwinian sense required some rehabilitation, dissatisfied 

 with the assumption of merely " accidental " variations, con- 

 fronted with evidence of definitely directed variations, Weismann 

 devised this theory of germinal selection. The personal selection 

 of the possessors of a plus or minus variation in any part means, 

 of course, that those org 3 nisms are favoured in which the corre- 

 sponding determinants within the germ-plasm are varying in a 

 plus or minus direction. But if there be inequality (in size 

 and assimilating power) among the homologous determinants, 

 and if there be fluctuations in the nutritive supply, there^may 

 come about a germinal struggle among the homologous deter- 



