Genetic and environmental contributions to dominance and subjective well-being in chimpanzees (Pan troglodytes)

Abstract

Zoo chimpanzees (Pan troglodytes) are restricted in their choice of social and physical environments. This allows for a strong test of environmental predictors of happiness including the chimpanzee-environment fit and the degree of relatedness between a chimpanzee and its enclosure mates. The interrelatedness of zoo chimpanzees permit the study of genetic and environmental contributions to Dominance and subjective well-being (SWB) and their common genetic or environmental causes. Demographic predictors such as age and sex and environmental predictors such as density of males and females, density of male and female kin, and how similar in personality a chimpanzee was to other chimpanzees in its enclosure were tested first. A series of two-, three-, and four-way interactions was also tested. First, the effects of these predictors on Dominance were tested. Next, these effects were tested on SWB after the variance SWB shared with Dominance was removed. Eight behavioral genetic models were then tested. These models incorporated genetic and environmental variance and covariance components and any significant predictors that were discovered in the previous environmental analysis. The relationship between age and Dominance was positive and stronger for males than females. The relationship between age and SWB was negative. The genetic model that had the best fit and most parsimony included additive genetic effects and non-shared environmental effects for Dominance and SWB. Zoo effects were negligible. Finally, the genetic correlation between Dominance and SWB was almost entirely due to shared genes. These findings are consistent with a model positing that Dominance and SWB arise from a common temperament and are differentiated by nonshared environmental influences. They suggest that happiness in apes and humans may be a sexually selected fitness indicator.