ECHOES OF BATS AND MEN 



echoes. The tenfold increase in the highest audible fre- 

 quencies shghtly more than offsets the increase in wave 

 length of sound in water. Thus we should expect the 

 porpoise to have only about a twofold advantage over 

 a bhnd man owing to the shorter wave lengths that he 

 within his repertoire of echo-generating sounds. Factors 

 other than wave length must therefore explain the ex- 

 pertness of porpoises at the art of echolocation, which 

 blind men, as we shall see in Chapter 6, also try to cul- 

 tivate. Perhaps they have simply learned individually 

 to pay more attention to echoes, or perhaps in their long 

 evolutionary history they have acquired ears and brains 

 that are better adapted in some way we do not under- 

 stand for sorting out echo components from the complex 

 mixture of sounds bombarding their ears. 



Echo Experts in the Air 



Porpoises are large, spectacular, exotic, and it is rel- 

 atively easy to accept the fact that they are capable of 

 doing wonders in their watery world. At large outdoor 

 aquaria they are trained to perform such circus tricks as 

 leaping out of the water through burning hoops, catch- 

 ing rubber balls or dead fish tossed to them by their 

 trainers, and even throwing something back to a particu- 

 lar person in the audience. No one who has ever watched 

 these performances, or even motion pictures of them, 

 can doubt the inteUigence, agility, or skill of porpoises. 

 But they do Uve in the water rather than in our medium, 

 the air. Consequently they seem somewhat more remote 

 from the bUnd man's problems than the other major 

 group of animals which make extensive use of echoes in 

 their daily hves. These are the bats— tiny mysterious 

 creatures and, let's face it, to many people repulsive 

 ones. Furry little mammals, resembUng mice except for 



26 



