The Position of Body Mass in a Network of Human Life History Indicators

Abstract

Body mass is widely recognized as a morphological trait which is important for fitness optimization both in humans and other animals. Here, we propose that body mass is a part of fast life history trajectory – the fitness optimization pattern which emerges from harsh environment with a function to maximize reproductive output. To test this prediction, we measured body mass index (BMI) and a set of life history indicators in a large sample of reproductive individuals (N = 1,504; 32% males; Mage = 27.20; SD = 9.2). The data were collected via an online survey. Bivariate correlations showed that BMI was positively related to reproductive success, childhood poverty, and short-term mating success; furthermore, it was negatively associated to physical health, age of the first menarche, and economic reasons against reproduction. The Network Analysis confirmed that BMI is positively related to short-term mating success and reproductive success, and negatively to physical health and economic reasons against reproduction. Furthermore, centrality metrics showed that BMI has relatively low centrality indices, and thus represents a peripheral node in the network. The present data confirm that body mass is a morphological trait which participates in the fast life history trajectory of fitness optimization. A body mass which is slightly higher than population mean (but below obesity levels) probably represents an adaptive response to depriving economic conditions in childhood and contributes to the maximization of reproductive fitness. Finally, we highlight that the relations between body mass and life history may differ between and within species.