4 EVOLUTION OF LIFE 1.3- 



a way that the arrangement or pattern of the processes remains almost 

 unchanged as the molecules pass through it. We see analogies in the 

 way that a waterfall or a human institution such as the Catholic 

 Church remains the same, though its components change. Our 

 business is to try to describe this arrangement or pattern of processes 

 that is preserved. It is this pattern that we call the life of the species. 

 The activities that go to make up one sort of life are not necessarily 

 all to be found in any one individual, still less in any part of an in- 

 dividual. The pattern is not to be seen in any single creature or 

 part. Though we speak of 'individuals' they are no more the final 

 units than are the cells, the heart, or the brain, the bones, hair, or 

 nails. A whole interbreeding population is the unit of life that tends 

 to preserve the type, assisted, in social species, by individuals that 

 play a part in the life without participation in reproduction, such as 

 worker-bees. 



A wide range of activities, therefore, goes to make up any one type 

 of life, and we shall only appreciate these activities properly if we study 

 that whole life as it is normally lived in its proper environment. The 

 way to study animals or men is, first and foremost, to examine them 

 whole, to see how their actions serve to meet the conditions of the 

 environment and to allow preservation of the life of the individual and 

 the race. Then, with this knowledge of how the animal 'uses' its parts 

 we may be able to make more detailed studies, down to the molecular 

 level, and show how together the activities form a single scheme of 

 action. 



A living animal is continually doing things. Even when it is asleep 

 it is breathing, its heart beating and brain pulsing, while countless 

 chemical changes go on throughout its tissues. The waking life, of 

 course, shows this restless action even more clearly. Animals may 

 indeed sometimes be still, but they are never wholly inactive. It is not 

 difficult to see startling glimpses of this activity if we watch animals 

 alive, especially when they are in groups. A hawk wheeling, a pond 

 full of tadpoles, or a crowd of people moving on a city street will 

 remind us that if we are to see the interesting side of life we have to 

 study activity and not, as is more easy to do and so often done, to 

 spend all our time examining the 'structure' or 'chemistry' of the dead. 



The peculiarity of this activity of animals is that much, perhaps 

 most, of it has the effect of maintaining the integrity of the body and, 

 indeed, even of increasing the bulk, or of reproducing more bodies 

 like the first (homeostasis). The search for food provides raw materials 

 giving to the muscles energy for further search. If the situation 



