Sex ratios and social evolution David C. Queller  Current Biology  Volume 16, Issue 17, Pages R664-R668 (September 2006) DOI: 10.1016/j.cub.2006.08.017 Copyright © 2006 Elsevier Ltd Terms and Conditions

Figure 1 An example of a population with more females (two pink genes) than males (two blue genes). No matter what the breeding system is, the offspring genes in the next generation must come half from female genes and half from male genes, so the average reproduction of the majority females is lower, and genes for producing females are therefore being selected against. The converse is true if males outnumber females. Current Biology 2006 16, R664-R668DOI: (10.1016/j.cub.2006.08.017) Copyright © 2006 Elsevier Ltd Terms and Conditions

Figure 2 The parasitoid wasp Nasonia vitripennis on its host, a fly pupa. Photo courtesy Jack Werren. Current Biology 2006 16, R664-R668DOI: (10.1016/j.cub.2006.08.017) Copyright © 2006 Elsevier Ltd Terms and Conditions