The research, led by Xin Huang and Martin Kuhlwilm of the Department of Evolutionary Anthropology at the University of Vienna, together with Simon Chen and Sojung Han, addresses a long-standing gap in evolutionary biology. Although individual great ape species have been studied for signs of selection before, few analyses have systematically compared the signals across the full clade using a consistent framework. Great apes are of particular interest because they occupy a remarkable range of environments, from the swampy forests inhabited by bonobos to the high-altitude mountain forests of eastern gorillas, and because their biology, behavior and reproductive strategies differ in ways that may have left measurable traces in their genomes. Understanding where selection has acted, and whether the same genes or gene categories were targeted repeatedly across lineages, offers a window into both the shared and idiosyncratic paths of ape evolution.

Technically, the study employed two complementary population genetic approaches. Recent positive selection, in which a beneficial mutation rises rapidly in frequency and drags nearby genetic variants along with it, was detected through genome-wide screens designed to identify the characteristic patterns of reduced variation and skewed allele frequencies that such sweeps produce. Long-term balancing selection, by contrast, maintains multiple versions of a gene within a population over extended evolutionary periods, often because heterozygotes enjoy an advantage or because varying conditions favor different forms at different times. This leaves a different signature: unusually high levels of genetic diversity clustered around specific loci. By searching for both signals simultaneously across all six lineages, the team could distinguish candidate regions shaped by recent environmental pressures from those under ancient, persistent constraints.

The results revealed a striking diversity of candidate loci. Genes potentially related to sensory systems appeared repeatedly, suggesting that the demands of seeing, hearing, smelling and tasting in different forest environments have driven adaptation in multiple ape lineages. Immune-related genes also featured prominently, consistent with the well-established role of pathogens as powerful selective agents in wild primate populations, where each species and subspecies encounters its own distinctive suite of viruses, bacteria and parasites. Environmental pressures such as diet and altitude left their mark as well, with candidate genes in gorilla lineages potentially reflecting the challenges of life at elevation and others pointing to the divergent dietary specializations that separate, for example, the highly frugivorous orangutans of Borneo and Sumatra from their African cousins.

Reproductive strategies emerged as another recurring theme in the selection landscapes. Great apes exhibit extraordinary variation in their mating systems, ranging from the relatively egalitarian social structure of bonobos to the pronounced sexual competition seen in chimpanzees and gorillas, and the solitary lifestyles of orangutans. Genes implicated in gamete biology, reproductive physiology and related traits showed evidence of selection in patterns that may reflect these differing strategies. The researchers emphasize that these are candidate loci, meaning they represent well-supported hypotheses about the targets of selection rather than definitive proof of adaptation in every case. Nevertheless, the consistent appearance of genes in these functional categories across independent analyses strengthens the biological plausibility of the findings.

Beyond cataloging individual genes, the study ventured into territory rarely explored at this scale across multiple ape species: the distribution of fitness effects, often abbreviated as the DFE. This statistical framework describes the spectrum of fitness consequences that new mutations carry, from lethal to beneficial, and provides a fundamental descriptor of a population’s genetic architecture. The analysis showed that the vast majority of non-synonymous mutations, those that change the amino acid sequence of proteins, fall into either the nearly neutral category, where selection is too weak to matter much, or the strongly deleterious category, where natural selection efficiently removes them from the population. This bimodal pattern suggests a relatively narrow middle ground of mildly deleterious mutations, with important implications for how genetic disease and load are modeled in endangered ape populations.

One of the study’s most intriguing findings concerns the correlations of these fitness-effect distributions across lineages. Closely related species and subspecies showed highly correlated distributions of fitness effects, indicating that the fundamental mutational landscape is shared among kin lineages and shifts gradually with evolutionary distance. Bornean and Sumatran orangutans, for example, diverged relatively recently and display correspondingly similar patterns, while comparisons spanning deeper evolutionary splits, such as between Asian and African apes, reveal greater divergence. This observation provides empirical support for using closely related species as proxies in conservation genomics, where the fitness consequences of mutations in one endangered population might be partly inferred from better-studied relatives.

The comparative dimension of the work also uncovered both novelty and recurrence. Some candidate genes and gene categories were lineage-specific, pointing to adaptations unique to particular species or subspecies and potentially explaining traits found in only one member of the clade. Others represented recurrent targets, selected independently in multiple lineages, which suggests that certain biological functions are repeatedly subject to similar pressures wherever great apes live. Distinguishing between these two modes of evolution is central to understanding whether adaptation proceeds mainly through the innovation of new solutions or through the redeployment of old ones, and the great ape selection landscapes assembled here offer a rich dataset for addressing that question.

The practical implications extend beyond basic science. All six great ape species are threatened with extinction, and several subspecies are critically endangered. Knowing which portions of the genome harbor functionally important variation under selection can inform conservation priorities, helping managers decide which populations to prioritize for protection or translocation to preserve adaptive potential. The finding that most protein-altering mutations are either effectively neutral or strongly harmful also carries a cautionary message: small, isolated ape populations may accumulate strongly deleterious mutations through drift, a process known as genetic erosion, making genetic monitoring an urgent component of species survival plans.

The study relied exclusively on previously published genomic data, requiring no new field sampling, and was made possible by substantial computational resources provided by the Life Science Compute Cluster at the University of Vienna and the Austrian Scientific Computing infrastructure. The work was funded by the Vienna Science and Technology Fund and the Austrian Science Fund. The authors stress that the analysis is a first detailed pass at cross-lineage selection landscapes in great apes, and the accompanying candidate gene lists, published as part of the open-access article along with extensive supplementary materials, are intended as a resource for the wider community. As genomic datasets for wild apes continue to grow in size and geographic coverage, the framework established here can be updated and refined, potentially extending to additional subspecies and to ancient DNA from primate populations that no longer exist.

For evolutionary anthropologists, the study reframes great ape genomes not as static records of shared ancestry but as dynamic documents of adaptation, each lineage’s DNA inscribed with the history of its struggles against pathogens, climates, diets and social pressures. For conservationists, it provides a genomic compass pointing toward the variation that matters most. And for anyone curious about human origins, it offers a crucial comparative backdrop: by understanding how selection has shaped the genomes of our closest relatives, researchers gain a sharper sense of which features of our own genomes are truly exceptional and which are simply the shared inheritance of a remarkable family of primates that once spanned the forests of Africa and Southeast Asia.

Bonobo societies are primarily characterized by their matriarchal tendencies, which manifest in unusual ways for a species where sexual dimorphism favors males. Conventionally, stronger, larger males dominate social hierarchies and secure preferential access to both mating opportunities and resources. However, in bonobo groups studied across the Democratic Republic of Congo—the species’ sole natural habitat—females break this typical mold. The research combined three decades of meticulous observations from six distinct bonobo communities, unveiling a rare social structure where female alliances systematically counterbalance male dominance. This aligns with longstanding, yet under-tested, hypotheses suggesting that female cooperation is central to understanding their elevated social status.

The key finding emerging from the longitudinal dataset of nearly 1,800 recorded conflicts between sexes was that females frequently formed coalitions—strategic social “gangs”—to collectively subdue males during contests. These coalitions overwhelmingly target males, forcing them into submission and actively reshaping dominance hierarchies. Notably, 85% of the observed coalitions involved female-female alliances directing aggression or intimidation towards males. By banding together, females could neutralize individual physical disadvantages, engineering an inversion of the expected male-biased power structure prevalent in most mammals. This behavioral adaptation offers new insights into the evolutionary pressures that may favor social bonding and strategic cooperation over brute strength.

Delving deeper into the behavioral ecology, the study reveals that female bonobos’ reproductive strategies intertwine intricately with their dominance tactics. Unlike many primate species where male monopolization of female reproductive cycles is common, bonobos exhibit concealed ovulation and reproductive autonomy. These factors hinder males’ ability to predict optimal mating times and enforce monopolies, thus reducing the incentive for coercive behaviors. Females thus maintain selective control over mating decisions, further amplifying their leverage in social interactions. The synergy between reproductive strategy and coalition formation emerges as a cornerstone of female empowerment, suggesting that evolution has favored nuanced social intelligence and alliance-building in bonobo females.

The formation of these coalitions is marked by intense, rapid escalation within moments of conflict, frequently evidenced by loud, piercing female vocalizations described as deafening by researchers. These vocal displays precede coordinated pursuits where females collectively harass target males through the dense forest canopy, at times inflicting severe or even fatal injuries. The ferocity and cohesion of these groups intimidate males and establish clear social boundaries, effectively regulating male behavior without relying solely on direct physical dominance. Such vocal and cooperative tactics reveal complex communication and social organization, underscoring the cognitive sophistication underlying bonobo societies.

Despite these compelling dynamics, the nature of female dominance in bonobos is far from absolute or uniform across all populations. The study highlights considerable variation, with females winning approximately 61% of observed conflicts on average and outranking 70% of males. However, these figures represent a spectrum of dominance rather than consistent, unchallenged rule. This suggests that female power is context-dependent and modulated by local ecological and social conditions. Far from presenting a monolithic matriarchy, bonobo societies reflect flexible, negotiated power relations where female high status is maintained through both alliances and reproductive strategies, but is periodically contested.

The implications of this research extend beyond primatology, challenging entrenched narratives about sex, power, and social hierarchy in mammals and, by extension, in evolutionary studies of humans. The demonstration that female social solidarity can invert typical male-dominated structures invites fresh perspectives on how cooperation among females might have shaped social evolution in our own lineage. It underscores the possibility that strategic alliance-building, rather than brute dominance alone, has been a critical driver in the emergence of complex social systems, particularly among species closest to humans.

Furthermore, the study’s methodology—compiling a vast longitudinal dataset from multiple wild populations and conducting rigorous statistical analyses of conflict outcomes—adds robust empirical weight to previously speculative explanations. By quantifying conflict patterns and linking them to social bonds and demographic variables, the researchers have pioneered a model for studying power dynamics in non-human animals that integrates behavioral ecology with sociobiology. This approach not only clarifies bonobo social organization but sets a precedent for multifaceted investigations of dominance and cooperation.

Intriguingly, many females involved in coalitions are unrelated immigrants to their groups, a fact that intensifies the unexpected nature of these bonds. Unlike kin-based alliances common in many species, this cooperation forms between strangers, highlighting the role of social learning, trust, and reciprocal behavior in constructing power networks. The rapid formation of coalitions during conflicts suggests that bonobo females possess remarkable social agility, enabling them to mobilize support swiftly in response to threats or challenges, a trait critical for survival in their complex jungle environment.

The researchers emphasize that female coalition formation is but one mechanism underpinning female empowerment among bonobos. Reproductive autonomy and concealed ovulation likely complement coalitionary behaviors by reducing male aggression and promoting social stability. Future investigations are poised to explore these interactions further, examining how fertility cues, mating patterns, and hormonal cycles influence female status and coalition dynamics. Such integrated studies promise a fuller understanding of the biological and social underpinnings of female power.

Despite the clarity gained, the evolutionary origins of this remarkable female solidarity remain enigmatic. The researchers acknowledge that why bonobos—out of all mammals—have evolved such cooperative female alliances remains an open question. This mystery offers fertile ground for future research into the evolutionary pressures unique to bonobo habitats and life histories that may have favored female coalition-building over traditional dominance hierarchies. Understanding these drivers may illuminate parallel processes in early human social evolution.

Ultimately, this new research into bonobo social dynamics offers a powerful reminder that power and dominance are multifaceted, context-dependent phenomena. The ability of female bonobos to wield influence in a male-sized world through strategic alliances reshapes foundational theories about social organization in mammals. By revealing the delicate balance between strength, cooperation, and reproductive strategy, the study not only enriches our understanding of bonobos but also invites profound reflections on the role of female solidarity in shaping the trajectories of social species—potentially including our own.

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Subject of Research: Animals
Article Title: Drivers of Female Power in Bonobos
News Publication Date: 24-Apr-2025
Web References: http://dx.doi.org/10.1038/s42003-025-07900-8
Image Credits: Melodie Kreyer / LKBP
Keywords: Bonobo social structure, female coalition, primate dominance hierarchy, reproductive autonomy, animal behavior, evolutionary biology, social bonds, sexual dimorphism, coalition formation, female empowerment, conflict resolution, behavioral ecology