Figure 5.

Summary of the data from Fox et al. (2010) concerning sex-specific influence of grandmothers on the survival of grandchildren. The influence of a grandmother's presence on a grandchild's survival is expressed as the log of the odds ratio of the probability of grandchildren surviving when a grandmother was present divided by this same probability when a grandmother was absent. Dotted horizontal line depicts the value corresponding to no survival effect. The presence of MGMs increased grandchild survival of both sexes combined (p = 0.0129, binomial test) with no difference between the sexes (Fisher's exact test, p = 1.0) and no tendency to favour granddaughters over grandsons (matched pair Wilcoxon signed-rank test, p = 0.58). In contrast, the presence of the PGM had no net effect on both sexes of grandchildren combined (p = 0.79, binomial test), but her effect differed between the sexes (Fisher's exact test, p = 0.005), favouring granddaughters over grandsons (matched pair Wilcoxon signed-rank test, p = 0.031) and having the harmful effect on grandsons (p = 0.019, Wilcoxon signed-rank test), which is predicted by SA-zygotic drive.