Kinds of Scientists 49 



in the last chapter, living things are the examples par 

 excellence of systems of organized complexity. This fact 

 in itself makes their study rather different and in some 

 ways more difficult than the investigations of the simpler 

 systems studied by classical physics and chemistry. Not 

 only are Hving systems typically complex, they also behave 

 in rather different ways over time. Most physical systems 

 are reversible in the sense of the homely proverb that 

 everything that goes up must come down. By and large, 

 the same equations are used to describe the upward and 

 downward motions. All that is necessary is to change the 

 sign from positive to negative. In the same way chemists 

 can make oxygen and hydrogen combine to form water 

 and can then turn around and split them apart again. 



Living things tend to go in one direction only. Typically 

 they grow from a very small cell to a very large group 

 of cells. The cells themselves differentiate into special tis- 

 sues and organs. Once such differentiation proceeds be- 

 yond a certain point, the cell can't go back again to its 

 primitive state. Finally deterioration and death set in, but 

 they are not the opposite of birth and growth in the sense 

 that falling is the opposite of rising or reduction is the 

 opposite of oxidation. 



Perhaps the most distinctive feature of the living world 

 is the process of evolution whereby entirely new organisms 

 of apparently ever greater complexity are constantly being 

 created. 



In the past these differences in the content of the basic 

 physical sciences, on the one hand, and the biological 

 sciences, on the other, led to considerable differences in 

 procedure and to quite obvious temperamental and in- 

 tellectual differences in the people who entered the two 

 fields. Now the separation between the physical and the 

 biological sciences is becoming increasingly artificial. For 



