1. In large populations each individual of the rarer sex would make a greater genetic contribution to the next generation (frequency-dependent selection). Hence equal numbers of males and females is the evolutionarily stable strategy. However in many situations a bias in sex allocation is favored in ways that are clearly predicted by theory (for example under certain circumstances some individuals in a population will do better by producing sons and others by producing daughters; in other circumstances all individuals may do better by producing more of one sex) [E. L. Charnov The Theory of Sex Allocation (Princeton Univ. Press Princeton NJ 1982);
2. Godfray H. C. J. and , Werren J. H., Trends Ecol. Evol. 11, 59 (1996);
3. Foundations of Social Evolution;Frank S. A.;[publisher's information],1998
4. Campbell D. R., Trends Ecol. Evol. 15, 227 (2000)].
5. Studies of sex allocation have provided some of the best quantitative evidence for the relative importance of selection at the gene individual kin and population levels [J. Seger and J. W. Stubblefield in Adaptation Rose M. R. and Lauder G. V. Eds. (Academic Press San Diego CA 1996) pp. 93–123 [publisher's information] ;