122 THE MEANING OF EVOLUTION 



the very end of its life that the grasshopper has wings, 

 and then they serve probably to aid in the search for 

 a mate. Among the birds flight began simply in sail- 

 ing out of the trees, into which the creature, still half 

 lizard, had crept to escape its enemy. The earliest 

 bird known to us had comparatively insignificant 

 wings. There was really more support in its tail than 

 in its wings, and this would distinctly indicate that it 

 glided more than it flew. It had claws also upon its 

 wings, and it was probably the case that this creature 

 crept into the trees, at least in its earliest forms, and 

 sailed down in a manner not unlike that employed 

 to-day by the flying squirrel. From such simple be- 

 ginnings came the wonderful power of flight in the 

 birds. 



Among mammals the attempt to escape from the 

 enemy has led to an interesting development, which 

 will be more fully explained in a later section when we 

 speak of the history of the horse. The early mam- 

 mals walked flat-footed, as we do on our feet and as 

 the raccoon and the bear do on theirs. Gradually, 

 however, as their enemies became more fierce and bet- 

 ter able to injure the larger mammals, the latter 

 gained in power of flight, and this gain consisted first 

 in rising from the toes, lifting the heels completely 

 off the ground. At the same time the leg and foot 

 were gradually lengthened. Doubtless in this way the 



