INTRODUCTION 



In the prehistoric beginnings of intelligent life, man must have been 

 confronted with three related problems: to win shelter, warmth, and 

 tools from his physical environment; to control the health and sickness 

 of his own body; and to produce food from the animals and plants which 

 he soon domesticated for his use. His mastery of these problems pro- 

 gressed very unequally. Inorganic objects are in general simpler than 

 biological organisms, and when the young sciences became something 

 more than a mere codification of practical recipes, their theoretical 

 structure was based on ideas derived from inanimate nature; the 

 earth, air, fire, and water of the Greeks, and the Cartesian mechanics of 

 the seventeenth century. The physico-chemico-mechanical system of 

 thought can be appUed naturally enough to the physiological problems 

 of health and sickness ; if we consider man's body as a going concern, 

 its workings can be investigated like those of a machine. The biological 

 sciences, at least those which attempted to provide causal explanations 

 of phenomena, at first concentrated their energies on this aspect 

 of Hfe, and tended to neglect the more difficult problems of the 

 reproduction and development of organisms, for which inorganic 

 parallels did not Ue so near to hand. During the nineteenth century 

 the dominant and most progressive biological outlook was concerned 

 with organisms as something essentially static, as machines for which 

 the passage of time meant no more than a few extra revolutions of 

 the wheels. 



By one of those paradoxes which are so frequent in history, it was a 

 purely mechanistic theory which directed attention to the non-mechan- 

 istic aspeas of living organisms and changed the centre of gravity of 

 biological thought. Darwin's theory of natural selection was so matter 

 of fact, and invoked only processes which were so acceptable to a 

 mechanistic attitude, that he was able to convince the world at large 

 that organisms do actually evolve. As soon as this was accepted, it 

 gradually dawned on biologists that Uving things cannot be considered 

 apart from time; their essential nature changes as time passes. Interest 

 flowed back towards the study of developmental changes and the 

 problems of reproduction. Science once more took up the investigation 

 of breeding and hybridization. The same current of thought spread 

 into physics, and the indestructible timeless atoms were analysed into 

 waves, in whose existence time is an essential element; and a temporal 



