114 THE EVOLUTION THEORY 



process of degenerating are, even in extreme cases, far too slight to 

 have any selection- value, and I cannot call to mind a single case in 

 which the contrary could be assumed with any degree of probability. 

 What advantage can a newt or a crustacean living in darkness derive 

 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 difference 

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

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

 quite 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 protrude beyond the surface of the trunk they 

 may prove an obstacle to rapid swimming, although that could hardly 

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

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

 the surface, they would no longer Ije a hindrance 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 tlie degeneration of disused 

 ]3arts in terms of a process which I called Panmixia. Natural selection 

 not only effects 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 conservative process of selection continues, the greater must ])e 

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

 perfect organ will be of less and less frequent occurrence as time 

 goes on. 



Now if this conservative action of natural selection secures the 

 maintenance of the parts and organs of a species at their maximum 

 of perfection, it follows that these will fall beloiv tins onaximum an 

 soon as the selection ceases to operate. 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 depths of our lakes, or to the 

 abyssal zones of the ocean, or into a subterranean cave-system. In 

 this case all selection of individuals ceases as far as the eye is 

 concerned ; it has no importance in deciding survival in the struggle 

 for existence, because no individual is at a disadvantage through its 

 inferior eyes, for instance, by being in any way hindered in procuring 

 its food. Those with inferior organs of vision will, ceteris paribus, 



