H. L. CARSON 31 



curs, the amount of recombination that can be produced may be 

 relatively much smaller. 



As natural selection operates with gene combinations, it fol- 

 lows that where the hereditary material of the species is faced 

 with a new environmental challenge, the success with which the 

 species meets this challenge depends to a very great extent on 

 its ability to form new gene combinations. In other words, the 

 possession of a high potential for recombination carries with it 

 a correspondingly high potential for rapid evolution, whereas 

 general inability to recombine the hereditary material implies 

 evolutionary stagnation and greatly restricts ability to alter the 

 composition of the gene pool. 



If one wants to interpret the recent past history of a species or 

 to predict how rapid and far-reaching an evolutionary change 

 might occur in it, it is of the greatest importance to know the 

 specific system by which it reproduces. If the system is a sexual 

 one, then some knowledge of the potential recombination which 

 might be accomplished in a local population of this species is 

 imperative. Thus, the geneticist views the species population in 

 part with a sort of x-ray vision — looking within to such matters 

 as details of meiosis — as well as assessing the importance of the 

 more extrinsic factors which affect recombination, such as the 

 mating system. 



An important point of emphasis is that estimates of the ability 

 to undergo recombination express only a potential ability — a 

 potential with which the species might respond should the con- 

 ditions arise which demand evolutionary aggression. If the con- 

 ditions do not arise, the status quo is likely to be maintained. 

 The potential may be there but never actually realized. The 

 possession of a high recombination potential by a species is no 

 more an automatic guarantee of further progress than is a high 

 mutation rate. 



To return to the point of view of the local population. As a 

 single generation is bridged by a population, the increment of 

 change possibly depends entirely on the wealth of gene com- 

 binations which are formed in the local pools. The widespread 



