Populations with Higher Sociality Lead to Higher Long-Term Population Growth in Time-Dependent Environments

Devikrishna N B, International Institute For Population Sciences
Rahul Mondal, International Institute for Population Sciences (IIPS)
Udaya Shankar Mishra, Centre for Development Studies, Trivandrum

Social interactions, within and between groups, substantially impact an organism’s vital rates and fitness. It is hypothesized that cooperative breeding, the system in which non-genetic parents help raise kids, improves reproductive success through efficient resource distribution. We study the effect of variations in sociality, defined by the order of kinship structure, on time-dependent long-term population growth rate. We investigate whether higher levels of sociality, characterized by broader kin networks, result in higher long-term population growth. We create matrix population models to examine how kin conditions affect population dynamics in 237 countries, using data from the United Nations World Population Prospects 2024. The sociality environment ranges from minimal (mothers alone) to extensive (mothers, grandmothers, daughters, siblings, aunts, and cousins) settings. We estimate the asymptotic stochastic growth rates and their sensitivities to various sociality levels by building Leslie matrices for each stage and their corresponding vital rates. Populations in high-sociality environments (with strong kin support) are expected to increase at greater and more steady rates. This finding would support the hypothesis that cooperative breeding systems greatly increase population fitness by highlighting the value of social networks in promoting long-term population stability and expansion.

Keywords: Population projections, forecasts, and estimations, Families, Unions and Households, Fertility, Mathematical demography

See extended abstract.