Chimpanzees are often described as being much stronger than humans, but just how much stronger are they? A popular factoid claims that chimpanzees are five to eight times stronger than humans. Does this mean that a chimp can lift a human and throw him around like a rag doll? Maybe if you ask Joe Rogan. Personally, I wouldn’t bet any money on that.

Such claims are based on outdated and flawed research, some of which date from over a century ago. In reality, the most recent studies suggest that chimpanzees are only about 1.5 times stronger than humans pound-for-pound. And since the average chimpanzee is much smaller than the average human, overall we aren’t all that weak compared to our closest relatives. However, chimps are no pushovers, as we’ll see.

Origins of the “Five Times Stronger” Myth

The myth that chimpanzees are five to eight times stronger than humans originated from a study conducted by biologist John Bauman in the 1920s. In Bauman’s era, every biologist and primatologist was convinced that chimps were much stronger than humans, but no one had proven it.

Bauman took it upon himself to conduct a formal analysis. He used a device called a dynamometer to measure the pull strength of chimpanzees at the Bronx Zoo. He found that one of the chimpanzees, named Suzette, was able to pull an impressive 1,260 pounds. Another larger chimp called Boma pulled 850 pounds one-handed. Bauman then tested human subjects, including ‘husky’ college football players, and found that none could pull more than 500 pounds with both hands, and only one of the subjects could pull 200 pounds one-handed.

To make things more astonishing, the chimps resisted participating in the study, often attacking and trying to pull apart the dynamometer. When they did use it, they did so from a clumsy position inside their cages, which offered little leverage, whereas the football players firmly gripped the device and gave it their all. These experiments convinced Bauman that chimps are blessed with superstrength that eclipses even the toughest humans.

It really seemed like chimps were at least five times stronger than humans. Or were they?

Subsequent studies have found that chimpanzees are not as much stronger than humans as previously believed. In 1943, Glen Finch of the Yale primate laboratory found that adult male chimpanzees were able to pull about the same weight as adult men. Once correcting for their smaller body sizes, Finch concluded that chimps are stronger than humans but not by a factor of five or anything close to that. Later studies in the 1960s suggested that chimpanzees were stronger than humans, pound for pound, but only by a factor of two.

Later, as other scientists scrutinized Bauman’s work more closely, they criticized the scientist’s clumsy measurement methods. They also noted that the exceptional pulls could be owed to the stressful conditions, which may have kicked off an adrenaline rush.

Chimps: not so strong, but still a force to be reckoned with

The most recent study that investigated chimp strength was conducted in 2017 by a team of researchers led by Matthew O’Neill, an anatomy and evolution researcher at the University of Arizona College of Medicine in Phoenix.

The team performed biopsies on thigh and calf muscles collected from three anesthetized chimps housed at the State University of New York at Stony Brook. The samples were painstakingly separated into individual fibers and then stimulated so the force that they generated could be measured. This initial reading showed that the muscle output was about the same as that of humans, on an individual muscle fiber basis.

Another analysis was performed on muscle tissue harvested from the pelvic and hind limb muscles of three chimpanzee cadavers. Using a technique called gel electrophoresis, the team broke down the muscles into individual muscle fibers and, again, compared the results with human muscle fiber data. They found that there was nothing special about chimp muscle. “Chimpanzee muscle is really no different than human muscle in terms of the force that individual fibers exert,” said O’Neill.

However, this study did reveal that there’s something truly special about chimp muscles and their strength.

These are the two types of muscle fiber: fast-twitch fibers (myosin heavy chain II), which contract very fast and generate more force in quick bursts, and slow-twitch fibers (also called red fibers), which contract more slowly for an extended period of time. Fast-twitch fibers are all about generating raw power fast, whereas slow-twitch fibers aren’t able to generate a significant amount of force but they’re great for endurance.

The researchers found that two-thirds of chimps’ muscle consists of fast-twitch fibers, whereas more than half of human fibers are slow-twitch. Chimps also seem to have longer fibers on average, especially around the arms, which also enhances their strength.

When the data on these muscle fibers were run through a computer simulation, the researchers found that chimp muscle is about 1.35 times more powerful than the human variety. The 1.35 figure corresponds well with the 1.5 times figure reached by reviewing the previous scientific literature.

So while the muscle fibers of chimps and humans aren’t all that different, their distribution varies considerably, with chimpanzees having a much higher fraction of fast fibers than humans, on average. This over-distribution of fast-twitch muscles may reflect chimps’ greater reliance on tree climbing and suspension for their survival.

There’s also a nervous system component to chimpanzee strength. Chimps have much less gray matter in their spinal cords than humans have. This gray matter contains many nerve cells that are connected to muscle fibers, allowing the brain to control and regulate muscle movement.

More gray matter allows humans to perform highly finely tuned motor tasks, such as using complex tools, throwing accurately, and manipulating small objects. Chimps, on the other hand, have much less control so when they actuate their muscles, it’s more of an ‘all or nothing’ affair, with each neuron triggering a high number of muscle fibers.

O’Neill says it’s likely other apes have a similar muscle strength to chimpanzees. A 2006 study, for instance, found that bonobos (our closest living relatives, alongside chimpanzees) can jump one-third higher than top-level human athletes, and bonobo legs generate as much force as humans nearly two times heavier. Indeed, when O’Neill’s team compared the muscle fiber in various mammals like mice, cats, dogs, horses, or macaques, they found that only two animals had more slow-twitch fibers: the lethargic slow loris and us humans.

But that doesn’t mean we’re slouches. In fact, the transition to more slow-twitch muscles likely coincides with evolutionary shifts in human locomotion, as our ancestors become better at walking upright and traveling over longer distances. While chimps were still busy swinging trees with their fancy biceps, humans were slowly spreading across the entire world.

Don’t mess with chimps: they’re vicious

However, the average male chimp weighs between 40 kg and 60 kg (88 lbs and 132 lbs), while an average 20-year-old American man weighs around 90 kg (200 lbs). That’s almost twice as much mass, which means that even with their pound-to-pound superior power muscles, chimps shouldn’t be stronger than humans. However, the average American doesn’t work out every day, swinging from canopy to canopy. In most cases, an average chimp from the forest is probably stronger than your average human. However, a jacked human is most likely stronger than an average-sized chimp.

And on top of their extraordinary strength, chimps can also be incredibly aggressive and violent in certain scenarios. In fact, biologists are studying chimpanzee violence quite closely as it may hold the key to unraveling the origin of warfare among humans.

Humans and chimpanzees are the only two species in the world known to attack each other in organized onslaughts. For instance, take the case of the bloody Gombe chimpanzee war between two tribes, the Kasekela and the Kahama, the latter a separatist group of chimps that split off from the Kasekela. Between 1971 and 1974, researchers led by famed primatologist Jane Goodall documented many organized killings in which groups of chimps from both tribes would raid the enemy group, often ambushing other chimps in a gruesome fashion.

Journalist Matthew Bian published a feature article on Discover detailing some of the events from this war.

“Another year passed until first blood was drawn on January 7, 1974, by a war party of six Kasekela males, who ambushed Godi, a southern male, as he was eating fruit from a tree. The northerners approached silently; Godi was not aware of their presence until it was too late. He jumped down and ran, with the Kasekela males on his heels. A chimp grabbed Godi’s legs and threw him to the ground. The other five caught up, then bit, pounded, and stamped on Godi while he was pinned to the ground. After 10 minutes of the whirling tornado of screeching chimps, the northerners left, leaving Godi on the forest floor to die from his injuries.”

“Over the next four years, more of the Kahama males were picked off in a similar manner. The second victim was beaten to death for 20 minutes by three males. Next was old Goliath, a high-ranking male back when the two chimp groups were united. Five Kasekela males, his former friends, turned on him. After the attack, his murderers repeatedly drummed on tree trunks, hurled rocks, and threw branches while calling out, as if in triumph. Goliath died from his wounds the next day.”

That’s not to say that all chimps do is go to war — far from it. In fact, violence comprises only a small portion of their lives. Chimpanzees spend much more of their time grooming, socializing, and foraging for food in non-aggressive ways, another way in which their behaviors mirror ours.

However, when they do decide to ‘go ape’, you better make sure you’re not on the receiving end. There are quite a few cases in which chimps have attacked humans with devastating consequences.

In February, 2009, 14-year-old chimpanzee Travis attacked Charla Nash, a friend of the woman who owned the 200-pound Travis as a pet. He tore off the woman’s nose, ears and hands, and blinded her. When the police arrived at her home in Connecticut, they shot Travis dead but Nash was tormented for life. In 2016, she had a face and hands transplant from deceased donors, but the tissue was rejected by her body.

In June 2012, Andrew Oberle, an aspiring primate researcher, was brutally attacked by two chimpanzees at a zoo in South Africa. The animals tore his flesh from head to toe and he nearly died.

Attacking chimps will use their canines to bite and tear at the victim, so that any body parts that stick out, such as hands, ears, nose, and even the testicles, are often ripped off during the onslaught.

According to the Jane Goodall Institute UK, pet chimpanzees are destructive and too dangerous to be kept as part of the family. It is extremely difficult to keep them stimulated and satisfied in a human environment — not to mention dangerous. Just don’t.

I think we can all breathe a sigh of relief we’re not living on Planet of the Apes.