Appendix I. 301 



So far, then, Professor Lloyd Morgan is in complete 

 agreement with previous writers upon the subject. He does 

 not doubt that the cessation of selection must always be 

 a cause of degeneration : the only question is as to the 

 potency of this cause, or the amount of degeneration which 

 it is capable of effecting. 



Taking, first, the case of bulk or size of an organ, as 

 distinguished from its organization or complexity, we have 

 seen that Weismann represents the cessation of selection — 

 even if working quite alone, or without any assistance from 

 the reversal of selection— to be capable of reducing a fully 

 developed organ to the state of a rudiment, or even, if we 

 take his most recent view, of abolishing the organ in lolo. 



Professor Lloyd Morgan, on the other hand, does not 

 think that the cessation of selection alone can cause reduc- 

 tion further than the level of " mediocrity '' in the first 

 generations — or, which is much the same thing, further than 

 the difference between the " birth-mean " and the " selection- 

 mean " of the first generations. This amount of reduction 

 he puts at 5 per cent., as " a very liberal estimate." 



Here, then, we have three estimates of the amount of 

 degeneration which can be produced by panmixia alone, 

 where mere size or bulk of an organ is concerned — say, 

 3 to 5 per cent., 10 to 20 per cent., and 95 per cent, to o. 

 At first sight, these diflFerences appear simply ludicrous ; 

 but on seeking for the reasons of them, we find that they 

 are due to different views touching the manner in which 

 panmixia operates. The oversights which have led to 

 Weismann's extremely high estimate have already been 

 stated. The reason of the difference between the extremely 

 low estimate of Professor Lloyd Morgan, as compared with 

 my own intermediate one, is, that he supposes the power 

 of panmixia to become exhausted as soon as the level of 

 mediocrity of the first generations has become the general 

 level in succeeding generations. In my view, however, the 



