The new study, which will appear in tomorrow's issue of the journal Nature, argues that in those cases, the reason is "the resources that allow females to breed are very limited," Hodge said, referring to the baby-raising help.
"Not all females can breed, so they're having to fight for the opportunity to do that."
Meerkat Dark Side
Even an untrained eye can easily tell that female meerkats are much more belligerent than males and spar much more frequently.
"There's certainly a lot of aggression in the female side of the family," said Caroline Hawkins, producer of Meerkat Manor.
"At first sight, they appear very cute. The typical image of a meerkat is standing on sentry duty, on its hind legs, looking to the horizon.
"But when you look beneath the surface, they're anything but cute," Hawkins added. "There's a real dark side, which is endlessly fascinating."
Proving why meerkats have this dark side has taken a lot of meticulous work.
Clutton-Brock and his group have kept tabs on births, deaths, genealogy, and individuals' places within meerkat hierarchies for more than 12 years.
The new study found size matters for females fighting their way to the top.
Larger females tended to stay dominant for longer, giving birth to far more pups.
That's not the case for males, where researchers found no such connection between size and dominance.
The dominant female is literally a pain in the butt for the rest of the females, biting them on the rump to keep them in line.
Forbidden to reproduce, these submissive females can quickly get on the dominant female's bad side by getting pregnant.
Subordinates that do often risk being evicted from the group—and on their own, they face almost certain death in the harsh desert climate.
Flower has on several occasions kicked her own daughters out of the group for giving birth.
Limited Resouces
There are other animals whose females are caregivers and yet aggressive, such as spotted hyenas and naked mole rats.
The study argues that this situation arises for the same reason as for meerkats.
"This should happen whenever resources that allow females to breed are concentrated," Hodge said.
"It might be a really good foraging area, where only females that have access to this area will be able to breed," she added.
"But in meerkats, it's having a group of helpers, and probably the same thing is true in, say, naked mole rats."
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