Final genotypes for monotonic acceptance rates.

<p>The lines in each panel show the mean genotype for each population size across the eleven possible offers. For each panel, black dots denote offer frequencies and conditional acceptance rates of human subjects, according to a meta-analysis of multiple behavioral studies. Because offers greater than 65% are rare in human studies, the rightmost dot comprises all offers of 65% or greater. <b>(a)</b> Frequencies of proposed offers without selection pressure. When the identities of reproducing agents were determined randomly, offer sizes were all equally frequent. <b>(b)</b> Rates of acceptance, conditional upon offer size, without selection pressure. When the identities of reproducing agents were determined randomly, but acceptance rates were constrained to be monotonically increasing, acceptance rates became linear with respect to offer size. <b>(c)</b> Frequencies of proposed offers with selection pressure. In contrast to the non-monotonic simulations, behavior shifts toward fairer offers, with modal offer sizes of 30%-40%. As in the non-monotonic simulations, larger populations tended toward lower offers than smaller populations. <b>(d)</b> Rates of acceptance, conditional upon offer size, with selection pressure. When the probability of reproduction was proportional to earnings, acceptance rates became non-linear with offer size, with concavity increasing with population size.