In the animal kingdom, physical prowess is mainly the core that enables them to climb up their respective hierarchal system. And this ranking is also followed by chimpanzees.

At least, for the male ones. In a recent study published on Oct. 14 in the Scientific Report, researchers found that male and female chimpanzees follow a completely different method when it comes to determining a certain ape's rank in a given hierarchy.

While the male chimps move up the ladder by challenging their superior, females accept their position and only increase in rank if those above dies. "We found that, after entering the adult hierarchy, there was a complete absence of successful challenges for rank increases among females," said Steffen Foerster, senior research scientist at Duke University and lead author on the study.

Researchers Sifted Through 40 Years' Worth Of Data On Chimp Behavior

The researchers admitted that it was quite the task to determine this "formal" system as female chimps tend to isolate themselves, spending their time alone or with their offspring. As such, it gave researchers little opportunities to gather clues in determining where a certain chimp ranks in their social order, said Science Daily.

"For a long time we've been aware that there really are differences in rank between females, but being able to quantify that has been hard because they really don't interact very often," said Duke evolutionary anthropology professor Anne Pusey, who is a senior author on the paper. They've only been able to achieve this breakthrough by sifting through 40 years' worth of daily records on wild chimpanzee behavior.

To determine where exactly does a chimp fall in the system, the researchers observed them as making a sound called "pant-grunt," a signal which means submission to a superior. Through this, they've been able to rank both male and female chimps and examine how the order shifted over time.

Female Chimps Opt For A Queue System To Avoid Risks That Aggression Brings

The researchers found that while a male's rank is at its summit during their prime around the age of 20, a female's position in the hierarchy gradually increases over time. Despite this finding, researchers are still speculating at how this hierarchal system have been initially established, reported Today.

Preliminary evidence suggests that females who has a mother in the group tend to have an upper hand. There are a lot of benefits that goes with how far a chimp - male or female - ranks up in the order.

Access to food, mates and a higher survival rate of offspring are among them. It seems that the main reason that females follow this queue system is the risk that aggression brings.

"It is potentially dangerous to challenge each other - you may get injured, your offspring may be killed if you have a little baby," said Foerster. "Finding that females actually do not fight for rank tells us how costly these challenges must be for them."