Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

The oldest hypothesis explained the identical number of male and female progeny from the viewpoint of the usefulness of such a sex ratio for the effectiveness of genetic recombination.It follows from the laws of combinatorics that a ratio of 1:1 allows the creation of a maximum number of various heterosexual pairs in a given population.The number of various heterosexual pairs influences the most important parameter of population genetics, the effective population size (V.3.2.1).In a great many respects, the value of this quantity is more important than the value of thenominal population size, i.e. than the absolute number of males and females.The greater the value of the effective population size in a certain population, i.e. the closer the ratio of the number of males and females is to one, the more effective are the processes of genetic recombination (see Equation (1) in Section V.3.2.1).In the extreme case, in a population consisting of a great many females and a single male, all the young would have the same father.It is obvious that this process would be highly undesirable from the viewpoint of the effectiveness of the processes of genetic recombination.

            The effectiveness of the processes of genetic recombination is certainly an important parameter from the viewpoint of the population or of the species.However, this parameter could be optimized during evolution only through the action of group or species selection, i.e. through processes whose effectiveness tends to be in doubt.In addition, from the viewpoint of the effective population size, the value of the secondary sex ratio is not important, but rather the value of the tertiary sex ratio, i.e. the ratio of the number of males and females at the time of sexual maturity.However, this ratio is rarely equal to one and, for example, in humans, frequently approaches a value of 1.4 because of male sterility and hypofertility (Wilda et al. 2000).