Adaptive personality calibration in a human society: effects of embodied capital on prosocial traits

Evolutionary theories of personality origins have stimulated much empirical research in recent years, but pertinent data from small-scale human societies have been in short supply. We investigate adaptively patterned personality variation among Tsimane’ forager-horticulturalists. Based on a consideration of cost-benefit tradeoffs that likely maintain variation in human prosociality, we hypothesize that individual differences in prosocial personality traits are facultatively calibrated to variation in "embodied capital"—that is, knowledge, skills, or somatic traits that increase expected future fitness. In support of this hypothesis, 2 components of embodied capital—physical strength and formal education—associated positively with Tsimane’ prosocial leadership orientation (PLO), a broad personality dimension representing gregarious cooperation, interpersonal warmth, and pursuit of leadership. Moreover, using pedigrees to compute heritability estimates, strength and education had additive effects on the heritable variance in PLO, which suggests that prosocial traits may be "reactively heritable" by virtue of their calibration to condition-dependent components of embodied capital. Although alternative explanations must be falsified in future research, our findings 1) provide one of the first demonstrations of adaptively patterned personality variation in a small-scale society and 2) illustrate the potential power of an adaptationist approach to elucidate the causal underpinnings of heritable personality variation.