32 The Selection Theory 



Holothurians have been modified and transformed in various ways 



in adaptation to the footlessness of these animals, and to the peculiar 



conditions of their life, and we must conclude that the earlier stages 



of these changes presented themselves to the processes of selection 



in the form of microscopic variations. For it is as impossible to 



think of any origin other than through selection in this case as in 



the case of the toughness, and the "drip-tips" of tropical leaves. 



And as these last could not have been produced directly by the 



beating of the heavy rain-drops upon them, so the calcareous anchors 



of Synapta cannot have been produced directly by the friction of the 



sand and mud at the bottom of the sea, and, since they are parts 



whose function is passive the Lamarckian factor of use and disuse 



does not come into question. The conclusion is unavoidable, that 



the microscopically small variations of the calcareous bodies in the 



ancestral forms have been intensified and accumulated in a particular 



direction, till they have led to the formation of the anchor. Whether 



this has taken place by the action of natural selection alone, or 



whether the laws of variation and the intimate processes within the 



germ-plasm have cooperated will become clear in the discussion of 



germinal selection. This whole process of adaptation has obviously 



taken place within the time that has elapsed since this group of 



sea-cucumbers lost their tube-feet, those characteristic organs of 



locomotion which occur in no group except the Echinoderms, and 



yet have totally disappeared in the Synaptidae. And after all what 



would animals that live in sand and mud do with tube-feet ? 



(7) Coadaptation. 



Darwin pointed out that one of the essential differences between 

 artificial and natural selection lies in the fact that the former can 

 modify only a few characters, usually only one at a time, while 

 Nature preserves in the struggle for existence all the variations of 

 a species, at the same time and in a purely mechanical way, if they 

 possess selection-value. 



Herbert Spencer, though himself an adherent of the theory of 

 selection, declared in the beginning of the nineties that in his opinion 

 the range of this principle was greatly over-estimated, if the great 

 changes which have taken place in so many organisms in the course 

 of ages are to be interpreted as due to this process of selection alone, 

 since no transformation of any importance can be evolved by itself ; 

 it is always accompanied by a host of secondary changes. He gives 

 the familiar example of the Giant Stag of the Irish peat, the 

 enormous antlers of which required not only a much stronger skull 

 cap, but also greater strength of the sinews, muscles, nerves and 

 bones of the whole anterior half of the animal, if their mass was not 



