DEVELOPMENT 213 



system has become stable and will no longer undergo change. 

 Now a developing ovum, with the substances in its environment, 

 is a chemical-physical system which undergoes changes. But in 

 these changes the substances of the system become chemically 

 more complex, the equilibrium is chemical-dynamic, and the 

 entropy of the system decreases locally. Clearly the chemical 

 and physical changes that occur during a development are not 

 such as those that a complex chemical substance would undergo 

 of itself : they are not " spontaneous " changes. 



There are chemical-physical transformations that are coupled 

 ones and examples are the photosynthesis of carbohydrate in the 

 cells of a green plant, or in the apparatus and materials assembled 

 by an experimental chemist. Here the dissipating energy of solar 

 or other light is brought into association with the system, CO 2 

 and OH 2. Of themselves the latter compounds would not 

 combine and of itself the energy of the radiation would dissipate. 

 But in the natural events and in the experiment the molecules of 

 CO 2 and OH 2 become energized by the radiation and their internal 

 energy is greatly increased. These energized molecules then 

 "spontaneously " dissipate their energy and this (as always) 

 becomes the occasion for a chemical reaction, which is that of 

 the combination of CO 2 and OH 2 (in the highly energized state) 

 to form carbohydrate. The internal energy of the latter com- 

 pound is less than that of the energized COo and OHo (and 

 that is *' Why " it was formed), but it is greater than that of the 

 unenergized CO 2 and OHo. 



And, therefore, the chemical and physical events of a developing 

 organic system are to be compared with the events that occur in 

 a system of coupled energy-transformations. Clearly there is 

 an agency which effects the couplings and it is this that is the 

 developmental organization. 



It is true that a chemical-physical may of itself and with very 

 great improbability, so change that its chemical structure may 

 become more complex, its internal energy may increase and 

 its entropy may decrease. The probability that this may happen 

 is of the order of that of such an event as follows : all the bricks, 

 mortar and other materials necessary for the construction of a 

 small house might be thrown on to the ground at random and 

 might still fall together, at random, into the form of the house. 

 We have never heard of such an occurrence, so very improbable 



