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 ? 
(y) 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 
