Summary: A new study shows that female spotted hyenas exhibit greater reproductive inequality than males when evaluated over multiple generations. While single-generation metrics align with the traditional Darwin-Bateman paradigm, showing higher short-term reproductive variation among males, long-term pedigree analysis reveals that high-ranking female alpha lineages accumulate disproportionate descendants. Within six generations, virtually an entire clan traces back to an alpha matriarch.
This multigenerational shift occurs because female hyenas inherit social rank from their mothers and stay in their natal clans, preserving privileges like priority food access, early reproduction, and longevity. Conversely, males disperse to join new clans and lose their maternal rank, preventing paternal lineages from accumulating long-term reproductive dominance.
Key Facts
- Short-Term vs Multigenerational Reversal: When measuring annual offspring count, male hyenas show higher reproductive inequality (following standard mammalian patterns). However, when tracking grand- and great-grandoffspring, female inequality sharply exceeds male inequality.
- Alpha Lineage Dominance: Alpha females account for roughly 10 percent of direct clan offspring, but 20 percent of grand-offspring. After six generations, nearly 100 percent of the clan stems from alpha matrilineal lines.
- Mechanisms of Matrilineal Rank: Female hyenas remain in their natal clans and inherit their mother’s social rank, giving them priority access to food, faster growth, shorter birth intervals, and longer lifespans.
- Male Dispersal Reset: Young males leave their natal clans to breed elsewhere, stripping them of inherited maternal rank and preventing privileged male lineages from compounding reproductive success across generations.
- Third Route to Female Competition: The study establishes matrilineal social inheritance as a distinct biological pathway driving female-biased reproductive inequality and intrasexual competition, alongside male pregnancy (seahorses) and reproductive monopolization (meerkats).
Source: IZW
In the animal kingdom, not all individuals produce the same number of offspring — and among mammals, this inequality is often greater among males than females. Among sexually reproducing species, males produce numerous, small and motile gametes (sperm), while females produce a small number of large and nutrient-rich gametes (eggs). In mammals, females also bear the physiological cost of pregnancy and lactation.
Because females invest far more in each reproductive event than males do, they are more selective about mating. Males benefit more from mating with as many females as possible and therefore compete intensely for access to mates.
This leads to conflicts between the sexes and gives rise to sex roles: males want to inseminate as many females as possible and as often as possible, and fight amongst themselves for access to the females, while females are selective and invest heavily in rearing their offspring. These predictions, formalised as the Darwin-Bateman paradigm, have been confirmed across many mammalian species.
The generational effect: Female spotted hyenas show greater inequality in reproductive success than males
Scientists from the Ngorongoro Hyena Project at the Leibniz-IZW and the ISEM analysed the pedigrees of eight spotted hyena clans in the Ngorongoro Crater. This involved over 2,700 individually identified hyenas spanning eight generations and 29 years.
The scientists investigated whether the pattern of greater inequality in reproductive success among males could be confirmed. Initially focusing on the annual number of offspring, they calculated inequality in reproductive success separately for males and females. This revealed that, as with most mammals, inequality was greater among males than females.
“This initially confirms the Darwin–Bateman paradigm, which predicts and explains greater inequality in reproductive success among males than females”, says the study’s lead author, Marta Mosna from the Leibniz-IZW.
“Our long-term pedigree enabled us to trace family lineages across generations. It was only when we looked beyond offspring to grand- and great-grandoffspring that the full picture emerged”, says Dr Eve Davidian, co-director of the Ngorongoro Hyena Project and a scientist at ISEM.
“Reproductive inequality among females increased with every generation we included. Privileged lineages didn’t just remain successful — they grew ever larger.”
High-ranking females produce and successfully rear more offspring than low-ranking females, and the gap widens dramatically when accounting for descendants across generations. In one generation around 10 percent of a clan’s offspring are directly descended from alpha females, whereas in the following generation as many as 20 percent are descended from an alpha grandmother.
After six generations, virtually all individuals can be traced back to an alpha line, making inequality in long-term reproductive success among females remarkably high.
This pattern is far less pronounced in the paternal line. Consequently, inequality in reproductive success shifts rapidly towards females across generations. Spotted hyenas therefore appear to follow the typical mammalian pattern only when offspring are considered; once grandchildren and great-grandchildren are included, females demonstrate greater inequality than males.
In spotted hyenas, social status influences reproductive success
The scientists of the Ngorongoro Hyena Project attribute this reversal to the social behaviour of spotted hyenas, specifically the social inheritance of privilege along the female line.
“In spotted hyenas, clans are organised in a strict dominance hierarchy, with an alpha female at the top. Offspring inherit their social rank from their mother,” explains Philemon Naman, field assistant with the Ngorongoro Hyena Project in Tanzania.
“A high rank confers advantages on both sexes in the early stages of life, such as priority access to food, faster growth and a higher survival rate.”
As females usually retain their maternal rank, high-ranking females benefit from these advantages in the long term: they begin reproducing earlier, have shorter intervals between births, and overall have a higher life expectancy than lower-ranking females.
This is where the two sexes diverge. “Males almost always leave to join another clan when they are ready to reproduce, losing their maternal rank in the process”, says Dr Oliver Höner, co-director of the Ngorongoro Hyena Project and scientist at the Leibniz-IZW.
“As a result, male spotted hyenas, unlike high-ranking females, do not convert a privileged family background into long-lasting reproductive success and lineages that accumulate descendants across generations.”
However, this reversal only becomes apparent when an appropriate long-term timescale is used in the data analysis.
“If you only measure offspring, you might conclude that there is little inequality among females and therefore weaker competition among them, and that males are the more competitive sex”, explains Mosna. “However, if you measure across generations, you see the opposite – finally explaining why females are the more competitive sex among hyenas!”
Female-biased competition and reproductive inequality have also been observed in other species – for instance, in seahorses, where males provide parental care, or in meerkats, where reproduction is monopolised by one dominant female.
“This study identifies a third route to the same outcome: the inheritance of social privileges along the female line”, concludes co-author Dr Alexandre Courtiol from the Leibniz-IZW. This form of maternal inheritance also exists in other species. Whether it leads to similar reversals in reproductive inequality is a question for future research.
Key Questions Answered:
A: The Darwin-Bateman paradigm predicts that males face higher reproductive inequality and competition because they produce abundant small gametes and invest less in offspring than females. Spotted hyenas match this rule in single-generation snapshots, but over multiple generations, female reproductive inequality far exceeds male inequality.
A: Male hyenas disperse from their native clan to breed in new clans upon reaching maturity. In doing so, they forfeit the elevated social status inherited from their mothers, effectively resetting their lineage’s competitive advantage with every generation.
A: Because social rank is inherited along female lines and compounds across generations, high rank yields exponentially higher long-term genetic representation. This enormous multigenerational payout drives intense intrasexual competition among females for dominance and status within the clan.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this evolution and social neuroscience research news
Author: Jan Zwilling
Source: IZW
Contact: Jan Zwilling – IZW
Image: The image is credited to 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 females. A mechanism driving reproductive inequality in humans and other animals is social inheritance of privilege.
Here, we show that this mechanism can reverse the male bias in reproductive inequality. 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, we show that reproductive inequality was lower among females than males when estimated annually but increased more strongly in females over generations, quickly reversing the sex bias to females.
Our findings suggest that social inheritance of privilege (i) is a powerful driver of sex differences in reproductive inequality and (ii) may explain why females are the more competitive sex in some species. We outline how reproductive inequality influences female and male reproductive strategies, intrasexual competition, and genetic evolution.
