Summary: A new long-term analysis of spotted hyenas reveals that reproductive inequality becomes female-biased when measured across multiple generations. Short-term measures, such as annual offspring counts, follow the classic Darwin–Bateman pattern with greater variation among males. However, pedigree analysis across generations shows that high-ranking females and their matrilines accumulate disproportionately more descendants. Within six generations, nearly an entire clan can be traced back to an alpha matriarch.
This multigenerational shift arises because female hyenas stay in their natal clans and inherit social rank from their mothers, maintaining advantages such as priority access to food, earlier reproduction, shorter interbirth intervals, and increased longevity. Males typically disperse to new clans, losing maternal rank and preventing paternal lineages from building comparable long-term reproductive dominance.
Key Facts
- Short-term vs. multigenerational patterns: Annual offspring counts show greater reproductive inequality among males, matching common mammalian patterns. But when descendants across generations are counted, inequality among females increases sharply and surpasses that of males.
- Alpha-lineage dominance: Alpha females produce roughly 10 percent of a clan’s immediate offspring, yet they are the matriarchs of about 20 percent of grand-offspring. Over six generations, a clan’s membership becomes nearly entirely derived from alpha matrilines.
- Matrilineal rank inheritance: Daughters inherit their mother’s dominance rank and remain in the natal clan, preserving privileges that boost survival and reproductive output.
- Male dispersal resets advantage: Males leave to join other clans before breeding, losing inherited rank and preventing long-term accumulation of lineage-level reproductive success.
- A third pathway to female competition: Social inheritance along the female line constitutes a distinct mechanism that can produce strong female-biased reproductive inequality, alongside other known routes such as male parental care or reproductive monopolization.
Source: IZW
Background: In sexually reproducing animals, differences in gamete size and parental investment typically shape mating systems and competition. Males produce many small gametes and often pursue many mating opportunities, while females invest more per offspring and tend to be choosier. These principles underpin the Darwin–Bateman paradigm, which predicts greater reproductive inequality among males in many mammal species.
Conflicts between the sexes and the resulting sex roles—males competing for mating access and females investing heavily in offspring—are well documented across mammals. Yet long-term pedigree data can reveal dynamics that single-generation snapshots miss.
Generational findings: Female reproductive inequality exceeds male inequality over time
Researchers from the Ngorongoro Hyena Project at the Leibniz Institute for Zoo and Wildlife Research (IZW) and the Institute of Evolutionary Sciences of Montpellier (ISEM) analyzed pedigrees from eight hyena clans in the Ngorongoro Crater. Their dataset includes more than 2,700 individually identified animals spanning 29 years and eight generations.
When the team calculated inequality in annual offspring numbers, males exhibited greater short-term variation, consistent with the Darwin–Bateman expectation. But extending the analysis to grandchildren and great-grandchildren produced a striking reversal: reproductive inequality grew markedly among females across generations, while it remained comparatively limited in paternal lineages.
High-ranking females consistently produced and reared more surviving offspring than lower-ranking females. Because rank is inherited and daughters stay in the natal clan, these advantages compound across generations. One generation after birth, alpha females accounted for about 10 percent of a clan’s offspring; two generations later, roughly 20 percent of grand-offspring descended from an alpha grandmother. After six generations, almost every individual in a clan could be traced to an alpha matriarchal line.
In contrast, paternal benefits dissipate because males typically disperse and lose their inherited status. Without stable paternal rank inheritance, male lineages do not accumulate descendants at the same multigenerational rate.
Social rank and life-history advantages
Spotted hyena clans are structured by strict dominance hierarchies topped by alpha females. Offspring inherit rank from their mothers, and early-life benefits of high rank include priority access to food, faster growth, and higher juvenile survival. Over the long term, high rank leads to earlier reproductive onset, shorter birth intervals, and greater life expectancy for females.
Because males generally leave their natal groups to breed elsewhere, the reproductive advantages associated with maternal rank are not carried forward along male lines. This asymmetry explains why female reproductive inequality compounds over generations, producing intense intrasexual competition among females for rank and dominance.
The study therefore refines our understanding of how reproductive inequality arises: measuring only immediate offspring can conceal powerful multigenerational dynamics driven by social inheritance. Similar female-biased competition has been observed in other species under particular social or parental-care regimes, but matrilineal social inheritance represents a distinct route to the same outcome.
Co-authors of the study note that social inheritance of privilege exists in other species, and future work should test whether comparable long-term reversals of sex-biased reproductive inequality occur elsewhere.
Key Questions Answered:
A: The Darwin–Bateman paradigm predicts higher reproductive inequality among males because they produce many small gametes and invest less in each offspring. Spotted hyenas conform to this pattern in single-generation snapshots, but multigenerational pedigree analysis shows that female reproductive inequality surpasses male inequality over time.
A: Male hyenas typically disperse from their natal clan to breed elsewhere, losing the social rank they would have inherited from their mothers. This dispersal prevents the accumulation of long-term lineage-level advantages.
A: Because rank and privileges are inherited along female lines and compound across generations, high-ranking females gain exponentially greater long-term genetic representation. This multigenerational payoff fuels intense competition among females for dominance within the clan.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The original journal paper was reviewed in full by editorial staff.
- Additional context was added by the editorial team.
About this evolution and social neuroscience research news
Author: Jan Zwilling
Source: IZW
Contact: Jan Zwilling – IZW
Image credit: Oliver Höner / Leibniz-IZW
Original research: Open access. “The legacy of privilege: Social inheritance reverses sex differences in reproductive inequality in the spotted hyena” by Marta Mosna, Alexandre Courtiol, Philemon Naman, Oliver P. Höner, Eve Davidian. Science Advances. DOI: 10.1126/sciadv.aee7880
Abstract
The legacy of privilege: Social inheritance reverses sex differences in reproductive inequality in the spotted hyena
Inequalities in reproductive success among females and males shape natural and sexual selection. For sexually reproducing species, the Darwin–Bateman paradigm predicts greater reproductive inequality in males than in females. Social inheritance of privilege is a mechanism that can drive reproductive inequality across generations.
Using a 29-year dataset spanning eight generations of spotted hyenas (Crocuta crocuta), a species in which social rank and privileges are inherited from the mother, the researchers show that reproductive inequality is lower among females than males when estimated annually, but increases more steeply for females across generations, quickly reversing the typical sex bias. These findings indicate that social inheritance of privilege can be a powerful driver of sex differences in reproductive inequality and may help explain why females are the more competitive sex in some species. The study outlines implications for reproductive strategies, intrasexual competition, and genetic evolution.