For most mammals, it’s the males who are dominant. They’ll compete fiercely with each other and a select few of the top males father most of the children. Females usually share motherhood more equally.
Spotted hyenas defy this rule. It’s the females who are at the top of society as they compete with each other and build huge dynasties.
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Scientists had previously only observed female dominance in species where the males do all the childcare, like with sea horses, or where the alpha female prevents the other females from mating, like with meerkats.
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But a new study by the Ngorongoro Hyena Project at the Leibniz-IZW and the ISEM has identified a third way. When social privilege is handed down from mothers to daughters, female power compounds over time, making them the animal kingdom’s ultimate nepo babies.
Hyenas, much like baboons or macaques, live in highly social groups known as ‘clans’ that can grow up to 90 members. Spotted hyena clans are matriarchal. The females grow larger than males and display their dominance through higher aggression.
As the females usually retain their maternal rank, alpha 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.
A female hyena automatically passes down her social status to her children. Higher-ranking cubs get priority access to food, grow faster, live longer and breed more.
Females stay in their home clan and retain their social status forever, whereas the males usually leave home to find a mate in a new clan. This is when they drop to the bottom of the ladder and lose all their nepo baby privileges.
For the first time, scientists have finally explained why female hyenas are the more competitive sex.
A 29-year study tracking 2,700 hyenas across eight generations in Tanzania showed that reproductive inequality among females increased with every generation. Privileged lineages didn't just remain successful – they grew ever larger.
If you look at just one year, males seem to have more variation in breeding, just like other mammals. It’s only when you track the grandchildren and great-grandchildren, high-ranking female lines take over.
In one generation, around 10% of a clan’s offspring are directly descended from alpha females. By the nextgeneration, as many as 20% are descended from an alpha grandmother. After six generations, virtually every single hyena can be traced back to the original matriarchs.
This results in extreme female reproductive inequality. When a small handful of privileged bloodlines monopolise the entire clan, lower-ranking female lines die out.
“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”, says the study's lead author, Marta Mosna from the Leibniz-IZW.
“However, if you measure across generations, you see the opposite – finally explaining why females are the more competitive sex among hyenas!”
