GERMINAL SELECTION 127 



of equilibrium that has once been attained by the determinant system 

 whenever it is disturbed ? 



It is difficult to give any confident answer to this question. We 

 cannot reach clearness on this point through our present knowledge of 

 the germ-plasm, because we possess no insight into its structure : we 

 can only draw conclusions as to the processes in the germ-plasm from 

 the observed phenomena of variation and inheritance. But two facts 

 stand in direct antithesis to one another, first, the high power of 

 adaptation possessed by all species, and the undoubted occurrence of 

 unrestricted persistence in a given direction of variation, as seen in 

 artificial selection, and in the disappearance of parts which have 

 ceased to function ; and, secondl}^ the great constancy of old-estab- 

 lished species which do indeed always exhibit a certain degree of 

 individual variability, but without showing marked deviations as 

 a frequent occurrence or in all possible directions, as they certainly 

 would if every determinant favoured by a chance increase in the 

 nutritive stream necessarily and irresistibly went on varying further 

 in the same direction. Or can the constancy of such species be main- 

 tained solely by means of personal selection, which is continually 

 setting aside all the determinants which rise above the selection-value 

 by eliminating their possessors? I was for long satisfied that this 

 was the true solution of the difficulty, and even now I do not doubt 

 that personal selection does, in point of fact, maintain the constancy of 

 the species at a certain level, but I do not believe that this is sufficient, 

 but rather that it is necessary to recognize an equalizing influence 

 due to germinal selection, and to attribute to this a share in maintain- 

 ing the constancy of a species which has long been well adapted. 

 I am led to this assumption chiefly by the phenomena of variation in 

 Man, for we find in him a thousand kinds of minute hereditary 

 individual variations, of which not one is likely to attain to selection 

 value. Of course the constant recurrence of reducing divisions 

 prevents any particular id which contains a varying determinant from 

 being inherited through many generations ; for so many ids are being 

 continually removed from the genealogical tree by the constant 

 rejection of the half of all ids of every germ-plasm, that only a sniall 

 part of the ancestral id remains in the grandchild, great-grandchild, 

 and so on. Certainly some of the ids of the ancestors compose the 

 germ-plasm of the descendants, and if all the determinants of one 

 of these ids had begun to vary persistently upwards or downwards in an 

 ancestor, then all the determinants of the relative id in the descendants 

 would possess the variation in an intensified degree ; and however 

 slowly the variation advanced it would attain selection- value in some 



