SELF-PRESERVATION AND GROWTH 357 



Drops of liquid having a limited mutual solubility or artificial 

 static coacervates cannot divide themselves spontaneously. 

 The forces of surface tension are always tending to make them 

 coalesce and it is only the presence of surface membranes 

 which, to some extent, prevents this from happening. How- 

 ever, as we know, dispersion of this sort may be achieved, 

 even in such static systems, by means of external influences 

 such as simple shaking, which may lead to emulsification. 



The dispersion of the primaeval gi^owing coacervate may 

 also have occurred in this way. However, as these were of 

 the nature of dynamic stationary systems the existence of 

 which was bound up with the occurrence of processes within 

 them, their dispersion may have been evoked by internal 

 factors. It may, for instance, have occurred when the osmotic 

 pressure, which was increasing rapidly owing to the hydro- 

 lysis of compounds of high molecular weight, became too 

 great for the strength of the surface layer of the drop. 



Thus, owing to the constant interaction of our original 

 systems with their environment, there must have occurred 

 a gradual increase in the amount of material organised in 

 the systems. But as this increase always occurred under the 

 influence of ' selection ' the only systems which were pre- 

 served for further evolution were those which were most 

 highly developed, so that the quality of this organisation was 

 always changing in a particular direction. The systems did 

 not merely become more dynamically stable, they also 

 became more dynamic. We may regard this phenomenon as 

 the third important step in the directed evolution of our 

 original systems on the way to the development of life. 



In the first stages of the evolution under consideration, 

 when one could study the fate of isolated coacervate drops 

 without taking into account their relation to other such 

 drops, the factors which Avere of paramount importance for 

 the prolonged existence of the drop in question as an open 

 system, for its self-preservation under conditions of constant 

 interchange with the surrounding medium, -were the relative 

 rates of the processes taking place within it and not the 

 absolute values of these rates. 



