108 WORLD-POWER AND EVOLUTION 



It is perhaps a misnomer to speak of these as crises, for each 

 of these three steps in evolution required a long time for its 

 consummation. Yet as we look backward into the dim vistas of 

 the past, the steps are so foreshortened that they appear like 

 genuine crises. They are, as it were, great slopes in a terraced 

 plain. For long periods the life of the world was confined to the 

 waters. Then during a relatively brief period, as geology counts 

 time, there came a transformation. The highest forms that 

 inhabited those ancient seas, that is, the fishes, gave rise to a 

 stock which left the water and made its home on the land. Then 

 our ancestors, for such they were, moved on once more across the 

 vast plain, rising here and there over smaller terraces, until at 

 last they began to climb to the warm-blooded condition. Another 

 vast stretch of plain and minor terraces brought them to the final 

 steep upward slope. At its base our ancestors were animals; at 

 its top they were men. But have we yet reached the top.'' More 

 likely we are now upon the very steepest part of the terrace. 

 Hitherto we have climbed upward because some unknown force 

 kept driving us. Now we are conscious of ourselves, and are able 

 to direct our movements. It is for us to say whether we will climb 

 straight upward, or whether, like many of the creatures of the 

 past, we will wander this way and that, and perhaps fail to be 

 among the chosen few who finally emerge at the highest level. 



Let us consider how each of these three great crises impressed 

 upon our ancestors the supreme importance of the air. Each, 

 as has been implied, was associated with profound climatic 

 changes. It was drought, for instance, which apparently drove 

 our fishlike ancestors out from the water upon the land and into 

 the air. There are today examples of types that are undergoing 

 just such a transformation. For example, the so-called lung 

 fishes live in tropical regions where a long dry season causes many 

 of the pools and streams to dry up. When this happens the 

 lung fish burrows into the mud and makes for itself a slimy 

 chamber where it lies coiled up for half the year. Like all other 



