Kinds of Scientists 51 



We have already seen that in our century the Ught turned 

 out to be somewhat less clear than Pope thought, but the 

 point to be made here is concerned with one of the inter- 

 esting side effects of the change from Newton to Einstein. 

 Men began to ask themselves why they had been so sure 

 that the Newtonian theory was "true." It now seems quite 

 clear that one of the really important reasons for preferring 

 Newton to Ptolemy was the greater simplicity and beauty 

 of the Newtonian scheme. Indeed, as Professor Edwin A. 

 Burtt has shown,^ the heliocentric theory of Copernicus 

 was adopted by most mathematicians and astronomers at 

 a time when it was no more useful for predicting ecUpses 

 and other heavenly events and actually less consistent with 

 certain other empirical observations (for example, the ab- 

 sence of stellar parallax) than was the classical earth- 

 centered theory. 



The idea that the simpler of two possible explanations 

 is the best is a very old one and was much used by the 

 medieval logicians. Such aphorisms as "Nature does noth- 

 ing in vain," or "Nature always goes by the most direct 

 route" probably go back to ancient times, and modem 

 physics has leaned very heavily on the same principle. 



The biologist is a good deal less certain about the 

 principle of simplicity as a guide to investigation or a 

 criterion of truth. In the first place, life presents itself in 

 an almost bewildering variety of forms from the bacterium 

 to the whale. Each species in this endless variety arose 

 apparently as a solution to a single common problem — 

 "how to survive in a hostile world." Each species adapts 

 itself to a particular part of the biosphere by developing 

 a particular set of attributes. The biologist has an intense 

 interest in these particularities and is often captivated by 

 what he can't help calling their "ingenuity," but he doesn't 

 find them simple. 



