220 THE MECHANISM OF LIFE 



mechanical energy of almost all animals that now exist on the 

 earth becomes frittered away uselessly in random, misdirected 

 movements which end in friction and dissipation as waste heat. 

 But let these movements be directed and planned, and the energy 

 that would otherwise be degraded tends to accumulate. The 

 tendency to utilise the activities of the animal sensori-motor 

 ^system in retarding the natural degradation of cosmic energy 

 may easily be traced even in the lower animals, and it operates 

 in the highest degree in human activities. 



Even among the lower forms of life we see it, however, in 

 everything that is called an adaptation — that is, in every device 

 which gives an animal greater power over inimical nature. The 

 change of coat colour from brown to white in an arctic mammal 

 as the winter approaches is clearly such an attempt. This is the 

 real meaning of adaptation, and one might discuss it at length if 

 it did not constitute the greater part of biological science. 



Obviously, adaptation attains a maximum in the human 

 •animal when the latter develops and perfects the use of tools. 

 We do not distinguish between the bodily weapon and the tool 

 or machine adapted or manufactured from inorganic materials: 

 these are, in their effects, as much adaptations as is the change 

 of coat colour from brown to white, or the conversion of a fold 

 of skin into a flying membrane in some squirrels. The ball- 

 bearings in the hub of a bicycle, or the use of grease in the axle- 

 boxes of a railway waggon, are adaptations ; they would not exist 

 apart from life ; they are the indications of life, and their effect is 

 to retard the dissipation of mechanical energy into waste heat by 

 minimising friction. We cannot think of any inorganic, physico- 

 chemical system that does this ; the essence of any such system — 

 that is, of any mechanism that " goes " of itself, or of any 

 aggregation of chemical substances that interact with each 

 other — is that the system tends as rapidly as possible towards 

 a condition of equilibrium in which the mechanism ceases to 

 " go," and the chemical substances cease to interact. 



Here we get our first concept by which we " explain " physical 

 happening: when water runs downhill; when combustible sub- 

 stances burn and apparently disappear into the air; when coal 

 burns in a fire and generates heat; when proteids and carbo- 

 hydrates decompose into water, carbonic acid, and mineral 

 nitrogenous salts; when a hot poker becomes cold, and so on — I 

 when these things happen, energy becomes degraded or entropyl 

 increases, and it is because entropy increases that they do' 



