Chimpanzees and humans: how are we different? What might the common ancestor of humans and apes have looked like, living in the Miocene (23-5 million years ago)? Why didn’t all primates evolve into humans? What’s the difference between monkeys and apes? The answers to these and some other questions are in this article.
Chimpanzees and humans: how are we different? Many cognitive scientists believe that humans’ ability to innovate by changing syntax generates much of the richness and complexity of our thoughts and ideas. This gap between humans and our closest primate relatives is just one of many.
“Give me an orange, give me an orange to eat, give me an orange to eat, give me an orange to eat, give me an orange to you.” That’s the longest string of words ever written by Nim Chimpsky, a chimpanzee who was raised as a human by scientists and taught sign language in the 1970s. He was the subject of Project Nim, an experiment conducted by cognitive scientists at Columbia University to see if chimpanzees could learn language.
After years of exposing Nim to all things human, the researchers concluded that although he had learned to express his demands—for example, for an orange—and knew 125 words, he could not fully understand language, at least as they defined it. Language requires not only vocabulary but also syntax, they argued. “Give me an orange,” for example, means something different than “give me an orange.” Humans understand this from a very early age; we have an innate ability to create new meanings by combining and arranging words in different ways. Nim lacked this ability, which seems to be true of all chimpanzees.
Humans are bipedal, while apes, except for brief periods of upright posture, walk on all fours. This is a colossal discrepancy.
Kevin Hunt, director of the Laboratory of Human Origins and Primate Evolution at Indiana University, believes that human ancestors stood upright to reach vegetation in low-hanging tree branches. “When Africa started to dry out about 6.5 million years ago, our ancestors were stuck in the eastern part, where the habitat became the driest,” Hunt told Life’s Little Mysteries. “The trees in the drier habitats are shorter and different from the trees in the forests: In these drier habitats, if you stand next to a 6-foot-tall tree, you can reach food. In the forest, if you stand up, you’re 2 feet closer to a 100-foot-tall tree, and that’s not going to do you any good.”
There are many significant differences between humans and chimpanzees. Dreamstime
So our ancestors survived in the dry, bushy areas of Africa. Chimpanzees in the forests did not.
Charles Darwin was the first to understand why the simple act of standing up was crucial to the human-ape split. One word: tools. “As soon as we became bipedal, we developed hands to carry tools. We started doing that only 1.5 million years after we became bipedal,” Hunt explained. Give it a few million years, and we’ll turn those rock fragments into iPads.
If you shave a chimpanzee and photograph its body from neck to waist, Hunt says, “at first glance you wouldn’t know it’s not human.” The two species have remarkably similar musculature, yet somehow, pound-for-pound, chimps are two to three times stronger than humans. “Even if we trained 12 hours a day like they do, we wouldn’t be that strong,” Hunt says.
One day in an African forest, Hunt watched an 85-pound female chimpanzee use her fingertips to snap off branches from an aptly named ironwood tree. It took both hands and all the strength he could muster to snap off a similarly thick branch.
No one knows where chimps get all that extra strength from. “Some of their muscles are positioned differently — the muscle attachment points are positioned for force rather than speed,” Hunt said. “That may be all that’s needed, but those who study chimp anatomy are shocked to learn that they can get so much more force from subtle changes in muscle attachment points.”
Alternatively, their muscle fibers may be denser, or there may be a physicochemical advantage to the way they contract. Either way, the result is clear: “If a chimp throws a big rock, and you come along and try to throw it, you just can’t do it,” Hunt said.
Herb Terrace, a primate cognitive scientist who led the Nim project, believes that chimpanzees lack a “theory of mind”: They cannot infer another person’s mental state, whether it’s happiness, sadness, anger, commitment to a goal, love, jealousy, or anything else. Although chimpanzees are very good at reading body language, Terrace explained that they cannot speculate about another being’s state of mind when body language is absent. “I think theory of mind was a big breakthrough for our ancestors.”
Why does he think so? It goes back to the linguistic skills of the chimpanzee Nim, who speaks sign language. Like an infant, Nim spoke in an “imperative mode,” demanding what he wanted. But infantile demands are not actually a hallmark of language. As humans get older, unlike chimpanzees, we develop a much richer form of communication: the “declarative mode.”
“Declarative language is based on conversational communication between a speaker and a hearer for the purpose of exchanging information,” wrote Terras. “It is supported by secondary rewards such as ‘thank you,’ ‘that’s very interesting,’ ‘I’m glad you mentioned that.’ In the case of declarative language, a theory of mind is clearly necessary. If the speaker and hearer could not assume that their interlocutors had a theory of mind, they would have no reason to talk to each other. Why bother if there is no expectation that your audience will understand what you have said?”
He added: “I don’t know of any examples of non-human animals speaking.” This limitation, perhaps more than any other, prevents a series of events like the one in the new film Rise of the Planet of the Apes. In the film, chimpanzees learn sign language – a realistic scenario. But it’s hard to imagine them using their newfound skill to discuss and plan a world takeover.
The chimpanzee genome was first sequenced in 2005. It was found to differ from the human genome it was compared to, nucleotide for nucleotide, by about 1.23 percent. That amounts to about 40 million differences in our DNA, half of which likely arose from mutations in the human ancestral lineage and half in the chimpanzee lineage as the two species diverged.
These mutations result in the dramatic differences in species we see today: differences in intelligence, anatomy, lifestyle, and, just as importantly, in their success in colonizing the planet.
Humans’ closest living relatives are apes, such as chimpanzees, gorillas, orangutans, and gibbons. We all shared a common ancestor that lived during the Miocene period (23-5 million years ago). Although scientists have no remains of this mysterious creature, what might it have looked like?
In other words, how big was our last common ancestor (LCA) and what did its skull, brain, legs, arms, and even fingers look like, based on the available evidence?
We don’t have all the answers. But the closest equivalents alive today may be gorillas and chimpanzees.
One big unknown is the size of the LCA, Christopher Gilbert, a paleoanthropologist at Hunter College at the City University of New York, told Live Science. That’s because ape fossils from the period during which the LCA lived are rare, a 2017 study in the journal Nature noted.
Early or “stem” great apes span a wide range of body sizes, from small gibbon-sized species to larger primates approaching the size of a gorilla, making it difficult to determine the size of the LCA without a better understanding of the evolutionary relationships and history of these species, said Gilbert, a co-author of the Nature study.
Great apes such as chimpanzees, gorillas (pictured), orangutans and gibbons share a common ancestor with humans. Mario Tama
Current evidence suggests that LCA was likely a quadruped. Fossils suggest that stem apes were capable of vertical climbing and had suspensory behavior, much like modern humans can use their hands to hang from tree branches. However, unlike all modern apes, which prefer to live hanging under or among tree branches, at least some stem apes were not specialized for suspensory behavior, lacking adaptations such as long, highly curved fingers and toes and highly mobile wrists, shoulders, and hips. This means that LCA may not have been specialized for suspension either, Gilbert said.
Some researchers have at times suggested that “maybe LCA was bipedal,” walking on two legs like a human, Thomas Cody Prang, a paleoanthropologist at Washington University in St. Louis, told Live Science. However, since LCA was quadrupedal like other primates, “it’s likely that it didn’t walk on two legs, but used all four.”
Stem apes showed a range of head shapes. Some had gibbon-like skulls with short faces, while others had longer faces reminiscent of primitive apes and Old World monkeys, such as baboons (genus Papio) and macaques (genus Macaca), Gilbert said. Still, “we know almost certainly that the brain size of LCA was smaller than that of humans,” Prang said. Because it was a quadruped, the head would not have been positioned on top of the body, as in bipeds, but would have been positioned more forward, like a gorilla or chimpanzee.
Bonobos, like chimpanzees, share 98.7% of their DNA with humans. USO
The hands and feet of early apes are often poorly preserved in the fossil record. However, “the upper limbs of early hominins, humans and our close relatives and ancestors, appear large and robustly built, consistent with forelimb-dominant locomotion, such as climbing and suspension,” Prang said. As for their legs, early hominins appear to have had short hind limbs more similar to those of great apes — gorillas (Gorilla gorilla and Gorilla beringei), chimpanzees (Pan troglodytes), orangutans (genus Pongo), and bonobos (Pan paniscus) — than to humans, he noted. In fact, early hominins appear to have been adapted for life in the tree canopy rather than on the open savanna.
As for the hand, in a 2021 study published in Science Advances, Prang and colleagues analyzed Ardipithecus, a 4.4-million-year-old early hominin fossil, and found that its hand was “the most similar to the chimpanzee and bonobo hand of any living human, great ape, or monkey.” This, in turn, may indicate that LCA had long, curved finger bones.
Humans, chimpanzees, gorillas and bonobos walk with their heels on the ground, suggesting that LCA does the same, Prang said.
This form of movement is also often associated with other traits seen in modern African apes — gorillas, chimpanzees, and bonobos — such as the use of knuckles to aid in walking and evolutionary adaptations for vertical climbing. “All the traits we can reasonably study suggest that the earliest hominins, and therefore likely LCA, were characterized by these same components of this adaptive package,” Prang said. “LCA was neither a gorilla nor a chimpanzee, but it was probably the most gorilla- and chimpanzee-like of all known primates.”
Why didn’t all primates evolve into humans? While we migrated around the world, invented agriculture, and visited the moon, chimpanzees—our closest living relatives—remained in the trees, where they ate fruit and hunted monkeys.
Modern chimpanzees have been around longer than modern humans (less than 1 million years, compared to 300,000 for Homo sapiens, according to recent estimates), but we’ve been on different evolutionary paths for 6 million or 7 million years. If we think of chimpanzees as our cousins, our last common ancestor is like a great-great-grandmother with only two living descendants.
But why did one of its evolutionary descendants achieve so much more than the other?
“The reason other primates don’t evolve into humans is because they do so well,” Briana Pobiner, a paleoanthropologist at the Smithsonian Institution in Washington, D.C., told Live Science. All living primates, including mountain gorillas in Uganda, howler monkeys in the Americas, and lemurs in Madagascar, have proven that they can thrive in their natural habitats.
Lucy belongs to one of the most famous early human species, Australopithecus afarensis, which lived approximately 3.85 to 2.95 million years ago. Field Museum; John Weinstein
“Evolution is not about progress,” said Lynn Isbell, a professor of anthropology at the University of California, Davis. “It’s about how well organisms fit into their current environment.” In the eyes of scientists who study evolution, humans are not “more evolved” than other primates, and we certainly haven’t won the so-called evolutionary game. While extreme adaptability allows humans to manipulate vastly different environments to suit their needs, that ability is not enough to propel humans to the top of the evolutionary ladder.
Take ants, for example. “Ants are as successful as we are, or more successful,” Isbell told Live Science. “There are many more ants in the world than there are humans, and they’re well adapted to where they live.”
While ants haven’t developed writing (though they did invent agriculture long before we came along), they are extremely successful insects. They’re just not very good at all the things that people are usually interested in, which is exactly what humans are good at.
“We have this idea that the fittest is the strongest or the fastest, but really all you have to do to win the evolutionary game is survive and reproduce,” Pobiner said.
A good example is the divergence of our ancestors from our chimpanzee ancestors. Although we don’t have a complete fossil record of humans or chimpanzees, scientists have combined fossil evidence with genetic and behavioral clues from living primates to learn about the now-extinct species whose descendants became humans and chimpanzees.
From an evolutionary perspective, this bonobo is doing just fine. Shutterstock
“We don’t have its remains, and I’m not sure we could confidently classify it as part of the human lineage if we did,” Isbell said. Scientists believe the creature was more chimpanzee-like than human-like, and likely spent most of its time in the forest canopy, which was thick enough to move from tree to tree without touching the ground, Isbell said.
Scientists believe that human ancestors began to differentiate themselves from chimpanzee ancestors when they began spending more time on land. Our ancestors may have found food by exploring new habitats, Isbell said.
“Our earliest ancestors, which split from our common ancestor with chimpanzees, would have been masters of both tree climbing and ground walking,” Isbell said. More recently — perhaps 3 million years ago — these ancestors’ legs began to lengthen and their big toes turned forward, allowing them to become primarily walkers.
“Some differences in habitat selection would probably have been the first noticeable behavioral change,” Isbell said. “To evolve bipedality, our ancestors would have moved into habitats that did not have closed canopies. They would have had to move more on the ground in places where the trees were more scattered.”
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The rest is human evolutionary history. As for chimpanzees, staying in the trees doesn’t mean they stopped evolving. Genetic analysis published in 2010 suggests that their ancestors split from the ancestral bonobos 930,000 years ago, and that the ancestors of the three living subspecies diverged 460,000 years ago. Central and eastern chimpanzees only began to diverge 93,000 years ago.
“They’re clearly doing a good job of being chimpanzees,” Pobiner said. “They’re still around, and as long as we don’t destroy their habitat, they’ll probably be around” for many years to come.
Primatologists explain the differences between monkeys and apes. At first glance, comparing monkeys and apes seems straightforward: modern primates have defining physical traits and behaviors that clearly place them in different categories.
Starting with living animals, these differences are easy to spot. Most monkeys have tails; some have prehensile tails, which means they can grab and hold things. They are quadrupeds, meaning they use all four limbs to move around. They have four limbs that are about the same length, and a flexible spine.
Monkeys can be divided into Old World and New World classifications based on where they live. Old World monkeys live in Africa and Asia, while New World monkeys live in Central and South America, according to the Pan African Sanctuary Alliance. Old World monkeys are also known as Afro-Eurasian monkeys, while New World monkeys are known as Neotropical monkeys.
On the other hand, great apes do not have tails. Their “upright” body plan allows them to stand upright and gives them disproportionate limbs with long arms and short legs. Conversely, humans, who are also apes, have long legs and short arms. Great apes also have larger brains relative to their body size than other apes, which is crucial for intelligence.
There is a significant difference in intelligence between monkeys and apes. Although monkeys are capable of complex thinking, they generally have lower cognitive abilities than apes.
At first glance, monkeys like this baboon (left) may seem similar to great apes like this gorilla (right), but experts explain that the two groups are very different. Mark Guitard and Mark Newman
Monkeys can be divided into great apes and lesser apes, depending on their size. Great apes include chimpanzees (Pan troglodytes), eastern gorillas (Gorilla beringei), western gorillas (Gorilla gorill ), and bonobos (Pan paniscus) — all of which live in Africa — and orangutans (Pongo), which live in Southeast Asia. Lesser apes include gibbons and siamangs, which live in Southeast Asia. Although humans are also great apes, this article focuses on non-human primates.
But if we consider the evolutionary history of apes and monkeys, the difference between them becomes even more unclear.
According to a review published in the journal Science in 2021, of which Almesia is the lead author, humans diverged from apes — specifically chimpanzees — between 9.3 and 6.5 million years ago.
But monkeys and apes diverged from their last common ancestor even earlier: between 23 and 34 million years ago, according to a 2013 paper published in the journal Nature. The authors analyzed the oldest known fossils of Old World monkeys and primates, found in the Rukwa Rift Basin in southwestern Tanzania: a partial jawbone with three teeth from an ape and a single molar from an ape. The team classified these new primate fossils, naming the ape Rukwapithecus fleaglei and the monkey Nsungwepithecus gunnelli. Geological dating of the rock layer in which these fossils were found indicates that they are about 25.2 million years old.
Still, there is much to learn about how primates evolved over millions of years. “The fossil record is open to interpretation and debate,” Malinsky wrote.
“It’s actually a lot more complicated than we think,” Almeciha said. “We don’t have as much information as we think to answer some of these questions.”
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