In the complex social worlds of wild chimpanzees, the strength and quality of female social bonds have emerged as a critical factor influencing offspring survival, a groundbreaking study reveals. Based on over three decades of detailed behavioral data from eastern chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, researchers have uncovered compelling evidence that females who maintain stronger social connections with other females prior to giving birth substantially increase the chances of their infants surviving through the vulnerable early years. This discovery challenges previous assumptions about primate sociality and sheds new light on the evolutionary underpinnings of maternal success and social behavior.
This research highlights the profound impact of social integration on infant viability, indicating that the degree of female social embeddedness can be as vital to offspring survival as genetic factors or immediate kinship bonds. In many mammals, the presence and support of closely related females such as mothers or sisters have been considered pivotal for maternal success. However, chimpanzee females, who typically disperse from their natal groups upon reaching sexual maturity, often lack close kin and must rely on social ties beyond family networks. The study’s lead author, evolutionary anthropologist Joseph Feldblum of Duke University, emphasizes how remarkable it is that females without kin still manage to forge beneficial social alliances that translate into measurable fitness advantages for their young.
The methodology involved sophisticated data and statistical analyses focusing on over 110 offspring born to 37 females monitored longitudinally. Researchers specifically assessed social behaviors—such as proximity and grooming interactions—in the year before parturition to establish a clear temporal relationship between maternal sociality and offspring outcomes. This approach excludes confounding variables related to postnatal social dynamics that might otherwise obscure causality, particularly as infant loss can itself alter social behavior. By concentrating on pre-birth social integration, the team strengthens the inference that maternal sociality independently predicts survival probabilities.
Results were striking: female chimpanzees whose sociality scores were twice the community average exhibited a 95% likelihood that their infants would survive the critical first year of life, a period notorious for the highest risk of infant mortality. Conversely, those with sociality scores significantly below average faced a 25% lower chance, with survival rates dropping to approximately 75%. Notably, the positive effect of social connectedness endured beyond infancy, persisting up to the weaning age of about five years, signaling long-term benefits stemming from maternal social engagement rather than transient alliances.
Notably, the survival advantage conferred by social integration was independent of kinship networks. The study carefully tested whether having close female relatives, such as mothers or sisters, within the group accounted for improved offspring survival but found no significant correlation. Similarly, involvement with male individuals in the group—who might offer protection or resources—did not predict infant survival. These findings illuminate the unique and pivotal role of non-kin female social bonds, underscoring that the quality of affiliative relationships among females, regardless of genetic relatedness, holds the greatest sway over reproductive success.
Mechanistically, the pathways through which female sociality exerts its protective effect remain to be fully elucidated. Several hypotheses are plausible based on primate behavioral ecology. Socially integrated females may experience less harassment or aggression from conspecifics, thereby reducing the stress and injury risks that can jeopardize offspring. Alternatively, strong social connections could enhance cooperative defense of vital resources such as food patches or shelter, ensuring better nourishment and safer environments for mothers and infants alike. The social networks may also mitigate infanticide risk from other group members by enabling collective vigilance and coordinated responses to threats.
Physiological and psychosocial factors are also likely contributors. Social bonds could alleviate maternal stress during pregnancy through neuroendocrine pathways, resulting in healthier gestation and more robust neonates. Access to social partners might improve nutritional intake via shared food sources or tolerance during feeding, supporting better maternal condition. Moreover, the stability of these social connections—as evidenced by their persistence before and after birth—suggests that enduring relationships foster a social milieu conducive to offspring vitality, rather than ephemeral alliances formed solely in reactive contexts.
The broader significance of these findings extends beyond chimpanzee biology and offers valuable insights into the evolution of complex sociality in humans and other primates. Human females, much like chimpanzees, sometimes leave their natal communities and face the challenge of establishing new social networks. The ability to form and maintain supportive non-kin relationships in novel environments may have been a critical evolutionary adaptation for maternal and offspring survival. This research therefore enriches our understanding of how cooperative behaviors and social support systems evolved to underpin reproductive success and species survival.
Joseph Feldblum points out that humans uniquely scale cooperative behavior to vast social groups, but at the core lies the fundamental adaptive value of female-female sociality. The parallels observed in eastern chimpanzees reinforce the notion that forming strong, tolerant social bonds—irrespective of genetic ties—constitutes a powerful survival mechanism. As modern human societies grapple with social fragmentation and mobility, understanding the evolutionary roots and benefits of social integration can illuminate strategies to bolster maternal and child health globally.
This study, published in iScience on June 18, 2025, exemplifies interdisciplinary collaboration employing quantitative behavioral analyses and long-term field observations. The rigor of examining pre-birth social metrics primes future research to identify causal mechanisms and to explore whether analogous patterns exist in other social mammals. It also invites a reevaluation of conservation priorities, highlighting the importance of preserving natural social structures alongside habitat to ensure the health and continuity of endangered populations.
In sum, the intricate tapestry of female chimpanzee social life, as unraveled over thirty years at Gombe, offers a profound testament to the evolutionary power of social bonds. By demonstrating a direct link between non-kin social integration and offspring survival, the study not only challenges traditional views on kin-based cooperation but also reinforces the view that sociality itself—far beyond genetic relatedness—is a cornerstone of primate reproductive fitness and, by extension, human evolutionary success.
Subject of Research: Animals
Article Title: Socially integrated female chimpanzees have lower offspring mortality
News Publication Date: 18-Jun-2025
Web References:
https://www.sciencedirect.com/science/article/pii/S2589004225011241
References:
Joseph T. Feldblum, Kara K. Walker, Margaret A. Stanton, Elizabeth V. Lonsdorf, Deus C. Mjungu, Carson M. Murray, Anne E. Pusey, Socially integrated female chimpanzees have lower offspring mortality, iScience, 2025, 112863, https://doi.org/10.1016/j.isci.2025.112863
Image Credits:
Photo courtesy of Madua Musa
Keywords:
Life sciences, Evolutionary biology, Infant mortality, Group dynamics
