The process of natural selection is defined from the standpoint of population genetics. Examples are presented to show how natural selection might act gradually to eliminate harmful mutant genes from the population or to maximize the reproductive potential of gene combinations which are successful in a given environment. A harmful mutant gene which confers some definite advantage in the heterozygous condition may persist in a state of balanced polymorphism. It is shown that balanced polymorphism is of limited significance, producing variation within the kind but as far as is known, no innovative evolutionary development of new kinds. Supposedly helpful mutations might conceivably accumulate in a population by action of natural selection, but such a process would be so exceedingly slow that it would not account for the major adaptations of plant and animal species. Although genetic drift might cause a more rapid shift in gene frequencies, it produces non-adaptive changes and is not a valid basis for evolutionary progress. It is concluded that natural selection may lead to variations within the created kinds but it gives no promise as a mechanism of evolutionay descent.