In the intricate societies of wild eastern chimpanzees, the strength and quality of social bonds among females have revealed profound implications for the survival of their offspring, challenging longstanding assumptions about primate social dynamics. A groundbreaking study recently published in iScience uncovers that female chimpanzees who engage in robust social networks with other females before giving birth exhibit notably higher infant survival rates, even when close kin relationships are absent. This discovery provides new insight into how social integration, distinct from genetic ties, plays a pivotal role in reproductive success within one of humanity’s closest living relatives.
The research team, led by Joseph Feldblum, an assistant research professor of evolutionary anthropology at Duke University, analyzed behavioral data accrued over a remarkable thirty-year period from Gombe National Park, Tanzania. This longitudinal approach enabled the scientists to probe the nuances of chimpanzee sociality with high resolution, focusing specifically on interactions such as proximity and grooming among 37 female chimpanzees and their 110 offspring. Crucially, the study emphasizes social engagement in the year preceding parturition, thereby isolating the influence of maternal social networks prior to the confounding effects of postpartum behaviors and infant mortality.
Traditionally, the benefits of sociality have been ascribed primarily to the presence of kin, given the evolutionary advantages of aiding genetically related individuals. However, this new study challenges that paradigm by demonstrating that in chimpanzee societies—where females typically disperse from their natal groups and relocate to unrelated communities—social bonds with non-kin females still translate into a considerable survival advantage for their young. This phenomenon is particularly striking given that female chimpanzees are generally less gregarious than their male counterparts, raising intriguing questions about the adaptive value of female-female sociality in these complex primate groups.
Quantitative analyses revealed that females with social integration scores twice the community average had a staggering 95% probability of their infants surviving the critical first year, the time frame during which infant mortality is highest. Conversely, females with social connectivity levels halfway below the community mean saw infant survival odds plummet to 75%. Remarkably, the positive effect of social integration extended beyond infancy, persisting up to the offspring’s fifth year, corresponding roughly to the weaning period. These findings implicate sustained social relationships as vital contributors to offspring viability and developmental success.
Efforts to discern whether the presence of close female kin—such as mothers or sisters—underpinned these survival benefits proved inconclusive. Similarly, associations with males, often thought to provide protection or resources, did not account for the observed advantages. Instead, the decisive factor was the strength and density of social connections with other adult females, irrespective of genetic relatedness. This points to the importance of social tolerance, cooperation, or mutualistic behaviors among unrelated individuals in these primate communities, shifting attention towards a broader spectrum of social mechanisms influencing reproductive outcomes.
Though the precise mechanisms by which sociality enhances offspring survival remain to be elucidated, several plausible pathways emerge from the data and existing primatological knowledge. Socially integrated females may experience reduced aggression and harassment from other group members, thereby minimizing physiological stress and injury risks. Furthermore, increased social connectivity might facilitate cooperative defense of critical resources such as food patches or territory, ensure better vigilance against predators or infanticidal threats, and enhance maternal physical condition through stress buffering and improved nutritional access during pregnancy. Collectively, these factors could create a more favorable prenatal and postnatal environment for offspring development.
The stability of these social affiliations beyond the peripartum period underscores that female chimpanzees maintain enduring relationships rather than transient alliances motivated by immediate reproductive needs. Post-birth social interactions—such as grooming and proximity—appear to be extensions of pre-existing bonds, indicating a complex social network structure that supports maternal success over extended time frames. This sustained connectivity likely fosters social support, alliance-building, and reputational benefits that contribute cumulatively to enhanced infant survival.
These insights bear significant implications for understanding evolutionary trajectories of social behavior, particularly in species with female dispersal patterns. The fact that chimpanzee females can realize reproductive benefits through integrating into new social groups absent of kin highlights a form of adaptive social plasticity. This plasticity may have been a crucial factor in shaping the social evolution of early hominins, wherein cooperation and alliance formation among unrelated individuals became central to survival and reproductive fitness.
Moreover, parallels drawn between chimpanzee sociality and human social behavior deepen our comprehension of the roots of human cooperation and social networks. Humans frequently experience situations where kin are unavailable—due to migration, urbanization, or social upheaval—and yet are able to establish strong, supportive social bonds that enhance wellbeing and offspring survival. By examining the underpinnings of similar behaviors in chimpanzees, researchers can better infer the evolutionary origins of human sociality, offering a window into how our species evolved complex cooperative strategies.
The study also calls attention to the evolutionary significance of non-kin cooperation in mammals, a domain often overshadowed by kin selection theories. The realization that females benefit reproductively from building and maintaining social networks with unrelated conspecifics invites further investigation into mutualism, reciprocal altruism, and social tolerance as drivers of evolutionary fitness. Unraveling these dynamics promises to refine theories of social evolution and mate competition in primates and other social animals.
Ultimately, this research not only advances primatology but also guides conservation strategies for endangered chimpanzee populations. Recognizing the critical importance of female sociality for offspring survival informs habitat management and group protection policies, emphasizing social cohesion as a key consideration in maintaining viable populations. The findings underscore the intricate interplay between social behavior and demographic outcomes, helping to preserve the rich social fabric essential to chimpanzee resilience.
This landmark study integrates behavioral ecology, statistical analysis, and evolutionary theory to paint a nuanced picture of how social bonds among female chimpanzees directly contribute to reproductive success. It challenges traditional kinship-centric models and highlights the evolutionary value of social networks beyond family ties. As we continue to explore the social lives of our closest relatives, such discoveries illuminate the deep-rooted connections between sociality and survival that resonate through the primate lineage, including our own species.
Subject of Research: Animals
Article Title: Socially integrated female chimpanzees have lower offspring mortality
News Publication Date: 18-Jun-2025
Web References:
https://doi.org/10.1016/j.isci.2025.112863
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.
Image Credits:
Photo courtesy of Madua Musa
Keywords:
Life sciences, Evolutionary biology, Infant mortality, Group dynamics
