NATURAL SELECTION 145 



from enemies. Now, these are all inconceivably difficult pro- 

 blems, but animal protoplasm in its simplest form has already 

 solved most of them : it can act as a lung taking in oxygen and 

 letting out carbonic acid gas : it is not particular as to what proto- 

 plasm it has to assimilate. As to enemies, if they exist, they are 

 no more, or little more, specialised than itself. But here it 

 becomes apparent that we have been trying to imagine what 

 cannot exist an animal without any adaptation to a special 

 environment. It must have some specialisation in order to lay 

 hold of the protoplasm it requires for food. If definitely animal, 

 it cannot be absolutely non-specialist. But though our com- 

 pletely generalised animal is an impossibility, several points have 

 come out clearly. First, of all the powers of the most complex 

 animals, how large a proportion is possessed by the simplest of 

 all ! secondly, how much of all the dowry of the simplest is its 

 heritage from ancestors less definitely animal ! How little is due 

 to lucky variations appearing first in it ! Consequently how easy 

 is the process of adaptation when only slight extensions or devia- 

 tions are required to meet a slight change of environment ! 



We will now take an animal of great complexity, a Peregrine 

 Falcon. Its adaptations are exquisite. But nearly the whole of 

 the sum total was accumulated before the birth of the individual 

 in question : on the top of the huge accumulation he stands and 

 faces the world. For generations past only slight improvements 

 here and there have now and then been wanted, the finishing 

 touches of an artist. Such adjustments have enabled the species 

 to contend against each slight increase in the stringency 

 of the conditions of life or each slight change in them. But 

 why has the increased stringency or the slight change been 

 such that a suitable variation was likely to arise ? To under- Nature of 

 stand this we must consider what the environment is. It is environ - 



ment 



made up mainly of the species in contact with the one we are 

 considering. Physical conditions, as far as evolution is con- 

 cerned, act only indirectly as long as they remain constant. A 

 good enough way of withstanding changes of temperature has, 

 let us suppose, been already secured. But to keep pace with a 

 rival species greater vigour is required and greater vigour implies 



