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Should Chimpanzee Behavior Challenge Human Exceptionalism?

When our kids were little, I always enjoyed our family trips to the zoo. As they grew older, our zoo visits became much less frequent and eventually came to an end. 

It had been years since my wife and I visited the zoo. But, now that we have grandkids, we once again find ourselves on zoo excursions. Hands down, my favorite exhibits are those that feature Old World and New World monkeys and the great apes (chimpanzees and gorillas). 

There is something about the behavior of the great apes that fascinates me. The few times I have had a chance to observe these creatures has been enough to convince me that chimpanzees and gorillas are intelligent, soulful creatures. In fact, sometimes when I watch their antics I get the distinct sense that I am seeing a bit of myself. These creatures do things that feel human-like.

Unlike my casual zoo observations, primatologists who study the behavior of the great apes make systematic and controlled observations of chimpanzee behaviors, both in captivity and in the wild. And in recent years, primatologists have recorded some remarkable and fascinating behaviors. Their observations provide abundant support for the intuition that many people have; namely, these creatures possess intelligence and sophisticated emotional capacity. 

Chimpanzees have been observed:

  • Making spears to hunt (which involves a six-step manufacturing process)
  • Making tools to extract termites from their nests
  • Making stone tools to break open nuts
  • Culturally transmitting technological know-how to the next generation
  • Using tools to fish
  • Occupying caves seasonally to avoid inclement conditions
  • Fabricating beds from tree branches with specific tensile and insect repellent properties
  • Successfully interacting with and exploiting natural wildfires
  • Using plants for medicinal purposes
  • Mourning their dead

Two recent studies add to this already impressive list of behaviors. In one study, a team from the Max Planck Institute of Evolutionary Anthropology (Leipzig, Germany) observed chimpanzees using insect remains to self-medicate their wounds and treat the wounds of other members of their group.1 In the second study, an international team of collaborators presented observations that suggest chimpanzee nut-cracking behaviors stem from social learning and claim that such behaviors evince cumulative culture in chimpanzees.2

These provocative results give us even greater insight into chimpanzee behavior, impacting how we think about our origins. Along these lines, these observations bear significance for biblical human origin models, including the RTB model.

Chimpanzees Use Insects to Treat Wounds
Beginning in 2019, the research team from Germany spent 15 months conducting field observations of the chimpanzees in Loango Park located in the West African nation of Gabon. On 22 occasions, they observed chimpanzees using a freshly made insect “paste” to treat wounds. In 19 instances, the chimpanzees self-medicated; in 3 instances, however, the chimpanzees treated others’ wounds.

Typically, chimpanzees began the wound treatment process by catching an insect and then immobilizing it by either squeezing the insect or putting it between their teeth. With its fingertips, the chimpanzee would rub the insect in its own wound or another chimp’s wound. Afterward, the chimpanzee would remove the insect remains from the wound. It wasn’t unusual for chimpanzees to repeat the treatment 3 to 4 times.

At this point, the research team has no idea of the kind of insect being used, let alone if it has actual medicinal properties. But the chimpanzees seem to behave as if it does, capturing and medicating with the same insect species time and time again.

This set of observations is the first that records chimpanzees using insects to self-medicate. And it follows earlier observations of chimpanzees using plant parts to treat themselves, either by ingesting them or applying them topically to the skin.

These observations are also important because they provide evidence for prosocial behavior in chimpanzees—behavior that benefits others. Up to this point, controversy surrounds the claim that chimpanzees engage in prosocial behavior, with some studies suggesting these creatures display this sophisticated behavior, which anticipates the empathy characteristic of modern humans. Other studies dispute this claim.

Either way, explaining the evolutionary origin of prosocial behavior proves to be problematic. The researchers note: “Prosocial behaviors have long posed a problem for evolutionary theory, because it was not immediately clear why organisms might help others in the face of selection operating in the interest of self.”3

Investigators hope that prosocial behaviors in chimpanzees will explain human prosocial behavior. Unfortunately, claiming that our prosocial behavior has its evolutionary antecedent in chimpanzees fails to explain how this behavior emerged in chimpanzees in the first place. All this observation does is displace the problem of accounting for prosocial behavior. It doesn’t solve it.

Chimpanzees Learn Nut-Cracking from Others
From 2007 to 2011, an international team of collaborators performed four field experiments with chimpanzees located in the Nimba Mountains of Guinea. They designed these experiments to determine if chimpanzees can independently invent nut-cracking technology or if this behavior is something they acquire through social learning. 

The group they chose to study show no evidence that they know how to use stones to crack open nuts. Yet other nearby groups do.

In previous studies, researchers have observed chimpanzees in captivity independently innovating a variety of different tools. But all of these examples involve simple tools used for simple tasks such as scooping and pounding. Nut-cracking is a much more complex behavior. And, to date, investigators have failed to record an instance in which chimpanzees in captivity have independently developed nut-cracking behaviors.

To follow up with these studies, the research team conducted field experiments that reflect chimpanzees’ natural ecological setting, unlike the artificial milieu chimpanzees find themselves in while in captivity. The researchers carried out four experiments at two locales during times of the year when food is either abundant or scarce. Each experiment presented chimpanzees with a different stimulus that could potentially lead to nut-cracking activities. The experiments included:

  • Setting out palm nuts next to stones
  • Setting out palm nuts and stones next to branches of palm fruit
  • Setting out palm nuts and stones along with cracked palm nuts
  • Setting out coula nuts next to stones

In all, they recorded 35 visits to the sites of the four experiments at both locales during times of high and low food abundances. The visits included small and large groups, groups that were made up of mixed gender, and groups comprised of mixed age.

None of these visits resulted in nut-cracking behavior or even behaviors that could be understood as a preamble to nut-cracking. Based on this null result, the researchers conclude that chimpanzees do not routinely independently innovate nut-cracking behavior. Instead, the behavior must be learned, and the knowledge must be transferred from one generation to the next. That is to say, chimpanzees display the capacity for cumulative culture.

The researchers conclude that their findings highlight the human-like behavior of chimpanzees, who appear to possess cumulative culture like that of modern humans. Yet there are significant and obvious differences in how cumulative culture is expressed in chimpanzees and humans. Our capacity for cumulative culture has led to an explosive advance of technology from primitive forms at the time of our origins to the technology that enables us to send people to the Moon and develop the wherewithal to take control of our own “evolution” and the evolution of other life-forms through genetic engineering and other techniques connected to synthetic biology. This same rapid progression of technology has not been observed for chimpanzees, indicating something fundamentally different about humans and chimpanzees—a difference in kind, if you will.

This same difference is also true when humans are compared with the hominins. Based on the archaeological record, one could make the case for cumulative culture in hominins such as Neanderthals. Yet hominid technology remained static as well. While humans may share the capacity for cumulative culture with chimpanzees and hominins, the consequence of having this capacity is unique in modern humans, most likely due to our unique capacity for symbolism and our capacity for combining symbols in an open-ended manner. Such qualities make us different in kind (not different in degree) from other creatures and could be understood from a theological perspective as a manifestation of the image of God.

Comparing Chimpanzee Behavior with Human and Neanderthal Behaviors
In other words, as remarkable as chimpanzee behavior may be, there remains a profound difference between chimps’ cognitive abilities and humans’ capacity for rational and symbolic thought, language use, and musical, artistic, and religious expression.

Primate behaviorist Thomas Suddendorf describes the comparisons of human and great ape behavior this way:

“We reflect on and argue about our present situation, our history, and our destiny. We envision wonderful, harmonious worlds as easily as we do dreadful tyrannies. Our powers are used for good as they are for bad, and we incessantly debate which is which. Our minds have spawned civilizations and technologies that have changed the face of the Earth, while our closest living animal relatives sit unobtrusively in their remaining forests. There appears to be a tremendous gap between human and animal minds.”4 

In attempts to understand the evolutionary origin of advanced cognitive behavior, scientists often compare the activities of Neanderthals (and other hominids) with those of modern humans. The tendency, then, is to regard the behavior of the hominins as progressing inexorably toward that of modern humans. Modern humans make tools, so hominin tool use represents a transitional state. Modern humans bury their dead, so Neanderthal burials are a prelude to human ritualistic burials. Modern humans hunt, so the scavenging practices of the habilines, erectines, and Neanderthals presage the sophisticated hunter-gatherer activities of modern humans.

But fully understanding hominin behavior requires that their activities also be compared to the great apes because, from an evolutionary perspective, humans share a common ancestor with these creatures. Chimpanzee behavior turns out to be closer to what we infer about hominin behavior from the fossil record, particularly for Homo habilis and Homo erectus (but also for Neanderthals), than it is to modern humans. The temptation is to see hominin behavior as transitional, representing a path to modern human behavior. Yet chimpanzees’ remarkable behaviors cluster with those of the hominins. This closeness in behavior distances the hominins from modern humans. Just because hominins made tools and engaged in other remarkable behaviors doesn’t mean that they were “becoming human.” Instead, their behavior increasingly appears to be animal-like, particularly when compared to chimpanzee activities, just as the RTB human origins model predicts.

Hominins and the RTB Human Origins Model
RTB’s biblical creation model for human origins views the hominins as animals created by God’s divine fiat, possessing intelligence and emotional capacity. Hominins employed crude tools and adopted some level of “culture,” much like baboons, gorillas, and chimpanzees. But they were not spiritual beings made in God’s image. That position—and all of the intellectual, relational, and symbolic capabilities that come with it—remains reserved for modern humans alone.

In other words, with respect to the hominins, the RTB model predicts that these creatures would be biologically similar to modern humans, but cognitively inferior. By extension, the RTB model expects a chasm to exist between the behaviors of modern humans and the hominins. That is to say, the RTB model predicts that human beings would be exceptional.

Don’t Chimpanzees Possess the Antecedents of Modern Human Behaviors?
Still, the remarkable behaviors observed for chimpanzees could justifiably be used to conclude that these creatures possessed the capacity for:

  • Abstract reasoning
  • Planning depth
  • Technological innovativeness

There may well be another explanation for their remarkable behaviors that doesn’t undermine the notion of human exceptionalism. Johan Lind from Stockholm University (Sweden) has demonstrated that animals engage in behavior that resembles flexible planning (which arises from the capacity for abstract reasoning, planning depth, and technical inventiveness) through associative learning. Researchers working in artificial intelligence (AI) have long known that associative learning can produce complex behaviors in AI systems that give the appearance of having the capacity for planning. In other words, planning-like behavior can emerge through associative learning and the same processes that give AI systems the capacity to beat humans in chess can, through associative learning, account for the planning-like behavior of animals such as the great apes.5 

Applying the insights from the work on AI systems, Lind developed mathematical models based on associative learning that he used to simulate results of the studies on the great apes and ravens which suggest these creatures display flexible planning like modern humans. He discovered that associative learning produced the same behaviors as observed for the great apes and ravens.

The results of Lind’s simulations mean that it is most likely that animals “plan” for the future in ways that are entirely different from humans. On the other hand, humans uniquely engage in bona fide flexible planning through advanced cognitive processes such as mental time travel, among others.

Could it be that the behaviors inferred from the archaeological records for hominins, including Neanderthals, also reflect an outworking of associative learning, instead of the flexible planning characteristic of modern human reasoning? 

It will take more than a trip to the zoo to find out.

Resources for Further Study

Endnotes

  1. Alessandra Mascaro et al., “Application of Insects to Wounds of Self and Others by Chimpanzees in the Wild,” Current Biology 32, no. 3 (February 7, 2022): R112–R113, doi:10.1016/j.cub.2021.12.045; James Gaines, “Chimpanzees Observed Applying Insects to Their Wounds,” Inside Science (February 7, 2022); Natalia Mesa, “Chimps Appear to Treat Others’ Wounds Using Insects,” The Scientist (February 7, 2022).
  2. Kathelijne Koops, et al., “Field Experiments Find No Evidence That Chimpanzee Nut Cracking Can Be Independently Innovated,” Nature Human Behavior (January 24, 2022): 1–11, doi:10.1038/s41562-021-01272-9; University of Zurich, “Cracking Chimpanzee Culture,” ScienceDaily (January 24, 2022).
  3. Mascaro et al., “Application of Insects to Wounds.”
  4. Thomas Suddendorf, The Gap: The Science of What Separates Us from Other Animals (New York: Basic Books, 2013), 2.
  5. Johan Lind, “What Can Associative Learning Do for Planning?” Royal Society Open Science 5, no. 11 (November 28, 2018): 180778, doi:10.1098/rsos.180778.