CATALYSIS AS THE EFFICIENT CAUSE OF EVOLUTION 253 



detrimental substances. Since most living things depend upon 

 molecules which must reach them through the living or dead 

 bodies of other bionts or through biological wastes or excreta, it 

 is obvious that, from the chemical standpoint, few existing indi- 

 viduals or groups can live alone. But underlying all these and 

 other complexities is the basic fact that evolution depends upon 

 heritable changes in biocatalysts, the successful ones tending to 

 survive, the unsuccessful ones to die out. 



The record of the rocks, imperfect as it is, represents what 

 actually has happened over millions of years with many widely 

 scattered populations of plants and animals, only some (probably 

 few) of which have left discovered fossil remains. It is impossible 

 to obtain an exact picture of the ever-varying conditions in 

 geologic times, though we have evidence of great movements in 

 the earth's crust, of glacial periods, of the probable existence of 

 an atmosphere containing more carbon dioxide than ours. Point- 

 ing out that the great defect of paleontology is that it cannot 

 directly determine any of the cryptogenetic facors instrumental in 

 the evolution of populations, because we cannot experiment with 

 fossil animals, G. G. Simpson states: 14 



"On the other hand, experimental biology in general, and genetics 

 in particular, have the grave defect that they cannot reproduce the 

 vast and complex horizontal extent of the natural environment and, 

 particularly, the immense span of time in which population changes 

 really occur. They may reveal what happens to a hundred rats in the 

 course of ten years under fixed and simple conditions, but not what 

 happened to a billion rats in the course of ten million years under 

 the fluctuating conditions of earth history. Obviously, the latter 

 problem is much more important. The work of geneticists on pheno- 

 genetics and still more on population genetics is almost meaningless 

 unless it does have a bearing on this broader scene. Some students, 

 not particularly paleontologists, conclude that it does not, that the 

 phenomena revealed by experimental studies are relatively insignifi- 

 cant in evolution as a whole, that major problems cannot now be 

 studied at all in the laboratory, and that macro-evolution differs 

 qualitatively as well as quantitatively from the micro-evolution of 

 the experimentalist. Here the geneticist must turn to the paleontolo- 

 gist, for only the paleontologist can hope to learn whether the prin- 

 ciples determined in the laboratory are indeed valid in the larger field, 

 whether additional principles must be invoked, and if so, what they 

 are." 



