Men's status and reproductive success in 33 nonindustrial societies: Effects of subsistence, marriage system, and reproductive strategy

Abstract

Social status motivates much of human behavior. However, status may have been a relatively weak target of selection for much of human evolution if ancestral foragers tended to be more egalitarian. We test the "egalitarianism hypothesis" that status has a significantly smaller effect on reproductive success (RS) in foragers compared with nonforagers. We also test between alternative male reproductive strategies, in particular whether reproductive benefits of status are due to lower offspring mortality (parental investment) or increased fertility (mating effort). We performed a phylogenetic multilevel metaanalysis of 288 statistical associations between measures of male status (physical formidability, hunting ability, material wealth, political influence) and RS (mating success, wife quality, fertility, offspring mortality, and number of surviving offspring) from 46 studies in 33 nonindustrial societies. We found a significant overall effect of status on RS (r = 0.19), though this effect was significantly lower than for nonhuman primates (r = 0.80). There was substantial variation due to marriage system and measure of RS, in particular status associated with offspring mortality only in polygynous societies (r = -0.08), and with wife quality only in monogamous societies (r = 0.15). However, the effects of status on RS did not differ significantly by status measure or subsistence type: foraging, horticulture, pastoralism, and agriculture. These results suggest that traits that facilitate status acquisition were not subject to substantially greater selection with domestication of plants and animals, and are part of reproductive strategies that enhance fertility more than offspring well-being.

Keywords: egalitarianism; evolution; hierarchy; reproduction; status.

Fig. 1.

Variation in the weighted effect of male status on RS, as a function of RS measure and marriage system (polygyny vs. monogamy) based on averaged coefficients (Table 2). Overall effect size based on intercept-only model. Before metaanalysis, all effect sizes were coded such that positive signs indicate positive contributions to RS (e.g., a negative effect of status on offspring mortality was coded as positive). Point size and line width are proportional to the number of results contributing to each weighted effect size.

Fig. 2.

Comparing weighted effect sizes of men’s status on measures of RS, from the model with subsistence as the only covariate, with effects of male dominance rank on mating success in nonhuman primates (16). Minimal variation was found across subsistence types, yet as a group, humans have significantly lower effects of male status on reproduction compared with nonhuman primates. Point size and line width are proportional to the number of results contributing to each weighted effect size.

Fig. S1.

Funnel plots on (A) the raw effect sizes and (B) the metaregression residuals, taken from the averaged model (Table 2). Solid vertical line indicates zero, and dashed vertical line indicates overall weighted effect size from the intercept-only model. Asymmetry in the funnel plot, specifically missing null or negative effects at low precision (lower left corner of the funnel), would indicate publication bias. Even though there seem to be a few outliers with large effects at low precision, Egger’s test did not reveal significant asymmetry for any model, hence publication bias does not seem to be a concern for this field.

Fig. S2.

Phylogenetic tree of the study populations with average effect sizes color coded and ranges indicated in parentheses for populations with multiple measures. Values for ancestral branches represent maximum-likelihood estimates (100), and the length of the legend bar indicates 50,000 y. Consistent with the low phylogenetic signals found in the models, variation within populations can exceed total variation in average effect sizes (e.g., Krummhorn, Piro, and Tsimane), average effect sizes do not visibly cluster, and all ancestral branches are reconstructed at similar values; this suggests that the association between male status and fitness depends on current socioecological conditions and not (vertical) cultural transmission.

Fig. S3.

Examples of MCMCglmm parameter estimates from the subsistence type-only model. (Left) Time series of the parameter as the Markov chain iterates. (Right) Posterior density estimate of the parameter (89). The fact that there is no trend in the time series indicates that the model has converged, yielding nice posterior distributions from which to calculate means and confidence intervals.