114 TIIK EVOLUTION TUKOKV 



pvocess ol' (li'm'iu'ratiiii;- are, o\'eu in oxtromo oases, far too sliji'ht to 

 have an}' soloctioi\-vahio, and I cannot call to niintl a single cast- in 

 which tho contraiy could be ass\nnod with any dooivc of prohahility. 

 What advantaiio can a newt or a crnstacenn living in darkness deri\e 

 from the fact that its eye is smaller and more degenerate by one 

 degree of variation than those of its co-partners in the struggle for 

 existence? Or, to use Herbert Spencer's striking illustration, how 

 could the balance between life and death, in the case of a colossus like 

 the Greenland whale, be turned one way or another by the tlitlereuce 

 of a few inches in tho length of the liind-leg, as compared with his 

 fellows, in whom the reduction of the hind-limb may not liaxe gone 

 (piite so far? Such a slight economy of material is as nothing 

 compared with the thousands of hundredweights the animal weighs. 

 As long as the limbs protrudt' beyond thi' surface of the trunk they 

 maj^ proN e an obstacle to rapid swinmiing, although that conld hardly 

 make much ditlerence, but as soon as the phyletic evolution had pro- 

 ceeded so far that they were reduced to the extent of sinlving beneath 

 the surface, they would no longer be a hindi-ance in swimming, and 

 their further reduction to their modern state of great degeneration 

 and absolute concealment within the flesh of the animal cannot be 

 referred even to negative selection. 



Years ago I endeavoured to explain the degeneration of disused 

 parts in terms of a process which 1 called Panmixia. Natural selection 

 not only etiects adaptations, it also maintains the organ at the pitch 

 of perfection it has reached by a continual elimination of those 

 individuals in which the organ in question is less perfect. The longer 

 this conservatixe process of selection continties, the greater must be 

 the constancy of the organ produced by it, and deviations from the 

 perfect organ will be of less and less frecpuuit occurrenci- as time 

 goes on. 



Ni)W if this conservati\e action of natural st^li'i'tion secures the 

 maintenance of the parts and organs of a siiecies at their maxinnmi 

 of perfection, it follows that these will /'uV/ hc/inf l/iii^ 'nut.ri'niit di ((,s 

 tiO(ni ((« the t:c/cctioii cciwen to o/icrati: And it does cease as soon as an 

 organ ceases to be of use to its species, like the eye to the species of 

 crustacean which descends into the dark di']itlis of our lakes, or to the 

 abyssal zones of the oei'an, or into a subterranean caxc^-systeni. In 

 this case all selection of individuals cc^ases as far as the eye is 

 concertuMl ; it has no importaiict^ in deciding survival in the strni>gK> 

 for (existence, lii^causi^ no indlxidual is a,t a disa(l\antag(^ through its 

 inferior eyes, for instance, by being in any way hiiuK^-ed in i)rocnring 

 its food. Those with infei-ior organs of vision will, ifVcrAs' /tarlbti;^, 



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