Figure 1

Increase in helping as a dominant trait relative to mating strategy and expected survival of adults between cohorts. The mean number of generations until the frequency of the helping allele equaled or exceeded 50% of the population are shown as ratios relative to single mating for 1 (black line), 2 (blue) or 5 (green) fathers (ratio = generations for x number of fathers/generations for 1 father). Where the blue and green lines exceed the black line, helping evolves faster with monogamy. Where they are less than the black line, helping increases more rapidly with polygamy. Regions of the graphs where individual lines do not extend indicate conditions where A never increased to the 50% criterion for the given numbers of fathers. Each point on the figure represents the mean of 100 individual simulations with those sets of values. Offspring are produced in cohorts of one (A) or five (B).