How Different Are Chimps From Ancient Humans?

An Israeli-led team has shown that bonobos can craft and use tools similar to those that our human ancestors utilized, raising the question: Do we really belong to separate genus?


“The Third Chimpanzee” is how scientist-scholar Jared Diamond dubbed the human species in his classic work. A new study by Israeli and American researchers suggests that maybe chimpanzees and bonobos – a close cousin of the chimpanzees - are indeed our sibling species, and a living evidence of the way our ancestors were some 2 million years ago.

In an experiment designed by Haifa University anthropologist Itai Roffman and his mentor evolutionary biologist Prof. Eviatar Nevo, also of Haifa U., along with colleagues, Sue Savage-Rumbaugh, Elizabeth Rubert-Pugh, and Avraham Ronen, two bonobos living in an Iowa sanctuary learned to make sophisticated stone tools that closely resemble those used by our ancestors about 2 million years ago.

"The behavior, culture, adaptation and survival strategies they used were previously thought unique to early Homo," says Roffman, an Adams Fellow of the Israel National Academy of Science,whose study was recently published in the Proceedings of the National Academy of Sciences (PNAS). The achievements of the two apes, named Kanzi and Pan-Banisha, were similar to those that our ancestors employed more than 2 million years ago, says Roffman.

The bonobo species is a great ape, which along with chimpanzees, are the lone members of the Pan genus.

For three months, Roffman worked with Kanzi, Pan-Banisha and several other bonobos raised by Dr. Sue Savage-Rumbaugh and Elizabeth Rubert-Pugh in the Iowa sanctuary, in order to push the limits of the apes' tool-making and tool-usage capacity. The researcher placed food within tree logs or buried it in deep soil, and the bonobos tried to retrieve the lost goods. Roffman and his colleagues wanted to simulate natural environments that our ancestors might have encountered over 2 million years ago; they placed rocks, leaved branches and antlers that might have been found in the ancient Savannas, in the apes' surroundings. The bonobos were required to crack open logs of wood just as humans had to crack open bone to extract the bone marrow or dig deep underground for tubers.

Kanzi, the star tool-maker

Kanzi, who already learned how to make basic tools in the 1990s, outperformed the rest of the crew. When digging for buried food, he used appropriate tools for different tasks. He relied on his hands for dry sands, sticks and antlers for wet soil and stones for hard, dry soil.

For breaking the logs, Kanzi produced two types of stone tools: heavy-duty tools (such as chopper-axes and wedges) and light-duty tools (such as drills and scrapers). This reflects the two main categories of stone tools our early Homo ancestors came up with over two million years ago.

"The resulting stone-tool wear patterns on the logs, which attest to this activity, show striking similarities to the patterns found on fossilized bones processed by early Homo 2.6 million years ago, hence its scientific importance," says Roffman.

"Kanzi had (already) learned to make tools, but not the specific tools which he currently created. This means that chimpanzees and bonobos have the potential for tool-making that ancient Homo had," says Roffman. Each tool shape fits its function. Kanzi used every tool appropriately and methodically to break open the food-filled log.

Chimpanzees and bonobos have also been shown to exhibit basic language skills. Researchers have already created a chimp lexicon, consisting of grunts and cries that together form what they consider to be meaningful words.

Some great apes, among them, Kanzi and Pan-Banisha, have been successfully taught to communicate with humans. Growing up over the past 30 years, under the care of Savage-Rumbaugh and Rubert-Pugh, the two bonobos live in an environment in which every object in their surroundings is tagged with a Lexigram (a geometric symbol). By adulthood, they were able to construct simple three- to four-word “sentences” referring to their past experience.

The chimp who ordered a salad

Kanzi once pressed on the appropriate symbols of his 400-word English Lexigram keyboard, to request that Roffman prepare him a salad. He selected the words “lemon juice," “lettuce," sugar," “salt," “raisins," “onions” and “celery." After receiving a salad lacking raisins, Kanzi once again pressed on the Lexigram keyboard, asking for the missing ingredient.

The two bonobos reacted to the most recent experiment by Roffman and colleagues, using their Lexigram keyboard. "Pan-Banisha referred to the buried food as a 'secret' and to the log as 'rock peanuts,'" says Roffman. “Kanzi also referred to a 'Coconut Surprise,' essentially making an analogy between the log of wood and the coconut shell, both containing food.

“The implications of this study on how we treat chimpanzees are far-reaching," says Roffman. “We must think of their culture as part of our own ancient human heritage. We must reconsider the question of chimpanzees living in captivity, (and instead consider) moving them to sanctuaries like the one in Iowa, where chimpanzees can live to their fullest early Homo potential."

The past decade has presented impressive evidence of the genetic proximity between humans and these great apes, pointing to a 98 percent - 99.4 percent shared genome. But even prior to the genetic analyses, studies in the last few decades have suggested that our closest relatives, chimpanzees and bonobos, are much more sophisticated and intelligent beings than widely perceived.

The first serious scientific research on chimpanzees goes back to Jane Goodall's renowned work in Tanzania in the 1960s. She first demonstrated to the scientific community that chimpanzees have what can be described as a personality, basic human-like expressions of emotion and reasoning, along with tool-making skills. Other researchers showed that chimps' different groups exemplify cultural variety, each population distinguished by the tools they use, their handshakes and other unique social behavior.

Israeli primatologist Dr. Tamar Ron finds the basic language skills, exhibited by chimpanzees and bonobos, baffling. She suggests that this indicates they have much more complex naturally-occurring communication skills among themselves that has yet to be deciphered.

Tool-making among chimpanzees and bonobos has been extensively researched in the last few decades. In Senegal, researchers have observed chimpanzees hunting bushbabies (Galago) using spears, and in another population in Bossou, Guinea, they identified chimpanzees using rocks as hammers and anvils. Another group of chimpanzees was observed chewing up leaves and then using them as sponges to collect water from small holes or rotting trees. Researchers have also seen chimpanzees digging 70 centimeter-deep holes into the ground, in search of water. Some chimpanzees use sticks to collect termites or honey; in Tanzania, the chimpanzees use them to dig up bulbs from the soil.

Chimps as herbalists

Chimpanzees and bonobos also know how to use herbs for medical treatment. They take advantage of plants to ameliorate diarrhea, and use rolled nettle leaves, smooth-side-out, by pushing them down their throat in order to catch parasites with the plant's stinging hairs.

“We can see these behaviors are a result of cultural development, since they are being transferred between individuals and from generation to generation”, says Ron.

In the 1990s, a few researchers proposed the hypothesis that the tool-making skills of chimpanzees and bonobos were similar to that of some of our Homo genus ancestors 2.6 million years ago. Kanzi and Pan-Banisha were both taught by anthropologist N. Toth and colleagues to make stone tools by direct percussion of one flint stone against another, and then to use them to cut their way to food inside a box. Kanzi employed this while inventing coarser methods such as smashing the stones on the floor or throwing them against other rocks.

Roffman has taken this one step forward, showing that bonobos possess even more sophisticated tool-making and tool-using abilities, in his experiment.

A few researchers, such as the late Prof. Morris Goodman, make the claim, based on this body of evidence, that chimpanzees and bonobos are humans' sibling species, and so should belong to the genus Homo rather than Pan.

“I think it is logical but not yet accepted by many," says Nevo. “In my view they are living fossils of early hominids which is a far more revolutionary and controversial view than the taxonomic issue," he says, admitting that this view is not shared by many pre-historians. “Most zoological texts will still regard them as a separate genus, with Pan very close to the genus Homo. However, we may need to alter this view in the future the more Pan's genetic similarity to humans unfolds.”

Ron, who was not involved in the research, offers a broader critique of the comparison of humans to chimpanzees and bonobos. “We make the mistake of being species-centric and constantly comparing other species to us humans. But doing so limits our ability to learn about them, since they undoubtedly have capabilities that we lack, such as their communication capabilities," says Ron. "Much of the research in this field suffers from this bias. We must learn to look at the nuances that cannot be found through comparison." 

A bonobo shows how stone tools are made.
Elizabeth Rubert-Pugh