150 THE MECHANISM OF LIFE 



there. Thus the succession of day and night, the order of the 

 seasons, changes in weather, such as storms, gradual or catas- 

 trophic geological changes, the vicissitudes of climate, tides, 

 ocean currents, winds, etc. — all these things are phases in a 

 " cosmic order," and are beyond the control of the feral animal, 

 or even of man. All that the organism can do is to avoid menace 

 to itself, or to take advantage of external changes in so far as it 

 can do so by some variation of bodily functioning. The real 

 meaning of the evolutionary process, from the biological point 

 of view, is the slow acquirement by the organism of the means 

 of varying its functioning, so that it can evade external changes 

 that are inimical to it or take advantage of other changes. 



When winter comes, many arctic animals respond to the 

 external changes by a change in the colour of the fur, say, from 

 brown to white. This renders them less conspicuous in a snow- 

 covered country, and the animal obtains an advantage in that it 

 is less easily seen by its enemies, and can the more easily approach 

 other animals that are its natural prey. Many fishes and other 

 animals hibernate during cold weather — that is, they seek shelter 

 of some kind, and lie in a passive condition, economising muscular 

 movements as much as possible. The respiratory and heart 

 movements slow down. Oxidation of the tissues is partially 

 inhibited, and the animal lives on its reserves of fat and proteid. 

 The advantage gained in such cases is that the animal is spared 

 the necessity of seeking food at a time when this is very scarce. 

 When a man passes rather suddenly from a tropical into a 

 temperate climate, he excretes much less water from his skin 

 and much more through his kidneys, and he thus economises 

 heat by an inhibition of evaporation of sweat. These are 

 instances of adaptations of the functioning of organs other than 

 those belonging to the sensori-motor system, and they do not 

 involve " psychological factors "■ — that is, they would be possible 

 in the absence of the higher parts of the brain, or at least they 

 need not include the activities of the latter organs. They do 

 not constitute behaviour. 



Neither do many adaptations that we call instinctive ones. 

 Thus the blowfly lays its eggs in fresh meat, so that when the 

 larvae hatch out they may obtain abundant nutriment. A bird 

 builds its nest in such a place and in such a way that it is difficult 

 to distinguish it from the surrounding objects, and so the con- 

 cealment of the eggs and young is an advantage. A crab casts 



