H. L. CARSON 29 



evolutionary point of view in any one generation, that is, at any 

 one time. Although transitory, the local population is always the 

 unit in which any new character first makes its appearance. It is 

 the only place where gene recombination can be effective as a 

 directive factor in evolution. Indeed, the local population, at any 

 one time level, always represents the point of contact between 

 the hereditary material of a species and its environment. It is at 

 this point that new genotypes are generated and this is where 

 they meet the immediate acceptance or rejection of the omnipo- 

 tent environment. 



The local population is not equivalent to any of the intraspe- 

 cific designations of the taxonomist, such a subspecies, local race, 

 or variety. The local population is not only suspended in time, 

 but it is usually much smaller than any of these. Furthermore, 

 even a local race may have a population structure which divides 

 it genetically into a series of partially isolated interbreeding 

 populations. A local population can, for example, be a hybrid 

 swarm; in such a case we are observing the release of an enor- 

 mous amount of variability through the recombination of genomes 

 which have been separated historically. The local population may 

 indeed have any one of quite a variety of past histories, which 

 will affect the amount of genetic recombination which occurs. 

 The fate of the genetic variability and of the continuing com- 

 position of the gene pool nonetheless is determined by the 

 inexorable laws of population genetics and the directive factors 

 of evolution working at a local level. 



Recombination in Populations 



Genetics is really the study of sexual reproduction. An enor- 

 mous amount of research on meiosis and chromosome cycles, 

 perhaps the bulk of it, was engaged in when only the vague 

 outlines of the evolutionary and genetic meanings of these chro- 

 mosome behaviors were clear. The details of sexual phenomena 

 in protozoa, for example, have been filled in with great elaborate- 

 ness as an adjunct to the ancient problems of taxonomic rela- 

 tionships and phylogenetic interpretations. The chromosome cy- 

 cles that one observes in the life history of an organism, how- 



