ON THE ORIGIN OF LIFE 



Given proteins and possibly nucleic acids in an ocean of 

 organic compounds, what primitive organizations might occur? 

 The physical problem is to get the necessary constituents in one 

 place at one time. It has been proposed by Haldane (1957) 

 that the cell constituents condensed on small oil droplets. Ber- 

 nal (1951) has favored condensation on clay, adsorption and 

 ion-exchange effects combining to achieve concentration. 



However, cells originating at interfaces would be rather flat. 

 A more appealing alternative based on the phenomenon of co- 

 acervation has been suggested by Oparin. In certain instances, 

 when two colloids are mixed at a pH between their isoelectric 

 points, the solution separates into two phases— one very poor in 

 colloids, the other very rich. Colloidal mixtures of gelatin and 

 nucleic acids will, in fact, form tiny droplets that superficially 

 resemble cells (Evreinova, Korolev, and Agroskin, 1959). When 

 lipids are present, a surface membrane may form; under some 

 conditions, pulsating vacuoles have been observed. Now these 

 droplets are not alive by any means. What has been demon- 

 strated is that a mechanism exists for wrapping proteins and 

 nucleic acids up as discrete blobs or cells. 



If the surrounding sea contained all the compounds neces- 

 sary for the molecules in a coacervate droplet to duplicate them- 

 selves, the droplet could grow. Its size might well be limited 

 by the action of currents and waves— if it grew too large, it 

 would be broken in two, only to grow again. This process could 

 not go on indefinitely, because the store of organic compounds 

 accumulated in the sea must someday have begun to give out. 

 Now suppose these little cells used up almost all of one com- 

 pound, which we shall call A. Now if perchance one photocell 

 was able to make its own A from B, then it could continue to 

 grow while all of its fellows starved. When B ran out, a lucky 

 mutant possessing a new enzyme that could make B from C 

 again would be able to thrive while others perished. And so, 

 applying a clever suggestion of Horowitz (1945), we can con- 

 ceive a scheme in which a very complicated set of enzymes was 

 developed backwards. The process possibly ended with the 

 metabolism of acetate and formate, two compounds probably 

 present in great quantities. Only now do we really need to 

 face the problem of the origin of photosynthesis in cells already 



