Tag: Max Planck Institute

  • Orangutan Self-Medication: How Great Apes Choose Plants to Treat Their Own Wounds and Infections

    On June 22, 2022, researchers at the Suaq Balimbing research station in Sumatra’s Gunung Leuser National Park heard a series of long calls from the canopy—the vocalizations male orangutans produce during dominance confrontations. The next day, they noticed that a flanged male orangutan named Rakus had a fresh wound on his right cheek, just below the eye, probably from a fight with a neighboring male. Three days later, they watched him do something no wild animal had ever been documented doing: he selected a specific plant—a climbing vine called Fibraurea tinctoria, known locally as Akar Kuning—ripped off its leaves, chewed them for 13 minutes, and then spent seven minutes applying the resulting juice directly to his wound with his fingers. He didn’t swallow the leaves during the application phase. When flies began landing on the wound, he covered it entirely with the chewed plant material, creating a poultice. The next day, he returned to the same plant and ate more leaves. Within five days, the wound closed. By July 19—roughly a month after the injury—only a faint scar remained. No infection developed.

    The paper, published in Scientific Reports in May 2024 by Isabelle Laumer and Caroline Schuppli of the Max Planck Institute of Animal Behavior, called it “the first known case of active wound treatment in a wild animal with a medical plant.” The emphasis on “active” is deliberate. Animals have been observed swallowing plants with medicinal properties before—chimpanzees chew bitter pith, gorillas and bonobos swallow rough leaves whole to mechanically dislodge intestinal parasites, Bornean orangutans rub chewed plants on their limbs. But those behaviors involve ingestion or generalized application. What Rakus did was topical, targeted, and sequential: he applied the plant’s juice specifically to the wound, on no other body part, repeated the application multiple times, and then covered the wound with plant material. He treated his own injury the way a human would treat a cut—clean it, apply medicine, bandage it.

    Why Akar Kuning matters

    Fibraurea tinctoria is not a random plant. It’s a climbing liana found across Southeast Asia—Indonesia, Malaysia, Thailand, Vietnam—and it’s used extensively in traditional medicine to treat dysentery, diabetes, malaria, and infections. Chemical analysis of the plant has identified furanoditerpenoids and protoberberine alkaloids with documented antibacterial, anti-inflammatory, antifungal, antioxidant, and analgesic properties. The plant also contains jatrorrhizine, which has antimicrobial and anticancer properties, and palmatine, which has anti-inflammatory and antiviral effects. This isn’t a plant that happens to have healing properties. It’s a plant whose healing properties are well-characterized enough that humans have been using it medicinally for centuries.

    Rakus’s population at Suaq Balimbing rarely eats it. In 21 years and roughly 390,000 feeding observations at the site, Fibraurea tinctoria appeared in only 0.3 percent of feeding scans. This wasn’t a plant the orangutan was already eating when he happened to touch his wound. He selected it specifically, used it in a way that doesn’t correspond to normal feeding behavior, and applied it exclusively to the injury. The researchers were careful to note that in 21 years and 28,000 observation hours, they had never previously seen an orangutan use leaves to treat a wound.

    How deliberate was it?

    This is the question the paper addresses directly and honestly. The behavior appeared intentional: Rakus selectively treated only his facial wound, not other body parts. He repeated the application multiple times. He used both the juice (liquid application) and the solid plant material (poultice). The entire process—feeding on the plant, applying the juice, covering the wound—took a considerable amount of time and was sustained across two consecutive days. The sequence is difficult to explain as accidental.

    But the researchers offer two possible origin stories, and they’re transparent about not being able to distinguish between them. The first is “accidental individual innovation”—Rakus may have been feeding on the plant, accidentally touched his wound while chewing, felt immediate pain relief from the plant’s analgesic effects, and then repeated the behavior because it worked. Under this model, the behavior was discovered by accident and reinforced by its consequences, which is how a lot of animal tool use and self-medication originates. The second possibility is social learning—Rakus wasn’t born at Suaq Balimbing. Male orangutans disperse from their natal area during or after puberty, sometimes traveling long distances. Rakus may have observed the behavior in his birth population, carried the knowledge across dispersal, and applied it when the situation required. If so, the behavior represents a cultural tradition transmitted between individuals, not an individual invention.

    The researchers can’t determine which explanation is correct because they don’t know where Rakus was born or what behaviors are practiced in that unknown population. This ambiguity is frustrating but honest—and it’s the central challenge of studying animal self-medication in the wild. You’re observing rare behaviors in long-lived animals across vast landscapes with limited coverage, and the most interesting questions (was it invented or learned?) require data from populations you may never have access to.

    The broader landscape of animal self-medication

    Rakus’s wound treatment is the most dramatic documented case, but self-medication in animals—zoopharmacognosy—is a recognized field with decades of evidence across multiple species and continents.

    Chimpanzees at multiple African field sites chew the bitter pith of Vernonia amygdalina, a plant with antiparasitic compounds, when they’re suffering from intestinal infections. The behavior is targeted: chimps eat it when sick and avoid it when healthy, suggesting they’re responding to internal cues rather than eating it as a regular food. Gorillas, chimpanzees, and bonobos swallow rough, hairy leaves from Aspilia and other plants whole and without chewing—the leaves pass through the digestive tract intact and physically dislodge intestinal parasites, which researchers have confirmed by examining fecal samples and finding parasites wrapped in leaf material. This is mechanical self-medication: the plant’s physical properties, not its chemistry, provide the therapeutic effect.

    Bornean orangutans have been observed rubbing chewed leaves of Dracaena cantleyi on their limbs, producing a lather that may have anti-inflammatory or antiparasitic properties. Capuchin monkeys rub citrus fruits and certain plants on their fur, potentially as insect repellent. Some moth species lay their eggs on alkaloid-rich plants when infected by parasitoid wasps, effectively medicating their offspring by ensuring the larvae consume antiparasitic compounds. Even fruit flies preferentially consume alcohol-containing food when infected by parasitoid wasps—the ethanol kills the wasp larvae developing inside them.

    The pattern across these examples is consistent: animals with no understanding of chemistry, pharmacology, or infection select specific substances with specific biological activity in response to specific health conditions. The behavior isn’t random foraging. It’s condition-dependent, substance-specific, and in many cases targeted to the affected body region. The question isn’t whether animals self-medicate. They do. The question is what cognitive mechanism enables it.

    What it means for the origins of medicine

    The earliest known human medical manuscript, from Mesopotamia around 2200 BCE, describes wound treatment with plant-based remedies. But if a Sumatran orangutan—separated from the human lineage by roughly 14 million years of evolution—independently applies a biologically active plant to a wound and covers it with a poultice, the implication is that the cognitive capacity for wound treatment predates the human lineage entirely. Laumer and Schuppli suggest that “medical wound treatment may have arisen in a common ancestor shared by humans and orangutans,” and that the behavior observed in Rakus may reflect deep evolutionary roots rather than a recent invention.

    The alternative—that Rakus and the Mesopotamian scribe independently arrived at the same solution—is possible but requires the same cognitive prerequisites: recognizing that a wound needs treatment, selecting a substance with appropriate properties, applying it specifically to the injury, and sustaining the behavior long enough for healing to occur. Whether the common ancestor had this capability or whether it evolved convergently in hominids and orangutans, the conclusion is the same: medicine didn’t start with humans. It started with primates who paid attention to what made them feel better and repeated it.

    Traditional healers in Indonesian Borneo have reportedly learned plant-based remedies by observing orangutan behavior—the knowledge transmission running from ape to human rather than the reverse. If Rakus learned his wound treatment from his natal population, and if human populations learned similar treatments from watching orangutans, then the same medicinal knowledge has been transmitted across species boundaries in both directions. The forest pharmacy has always been open. The question is who figured out the inventory first.

    We cover orangutan self-medication alongside baboon politics, ant collective intelligence, and the full landscape of animal cognition across our Animal Culture & Knowledge course—including why the first pharmacist may not have been a person. It may have been a primate with a cheek wound and the sense to reach for the right vine.

  • Cuttlefish Camouflage: How a Colorblind Animal Produces the Most Sophisticated Disguise on Earth

    A cuttlefish has up to millions of chromatophores in its skin—pigment-filled elastic sacs, each attached to a ring of tiny radial muscles, each muscle controlled by a small number of motor neurons that extend directly from the brain. When those neurons fire, the muscles contract, stretching the chromatophore from an invisible speck roughly a tenth of a millimeter across to a visible disc up to 1.5 millimeters in diameter, displaying the pigment inside. When the neurons stop firing, the elastic sac snaps back to its resting size. The whole process takes less than a second. There are three color classes of chromatophores—red, yellow/orange, and brown/black, depending on the species—arranged in layers across the skin. Beneath them sit iridophores, cells packed with reflective protein platelets that produce metallic blues, greens, and iridescent effects through thin-film interference. Beneath those sit leucophores, white reflecting cells that scatter all incoming wavelengths equally, providing a neutral base canvas.

    Three layers. Millions of individually addressable cells. Direct neural control from the brain. The result is the most sophisticated dynamic camouflage system in the animal kingdom—an animal that can transform its color, pattern, and three-dimensional skin texture in a fraction of a second to match virtually any natural substrate it encounters.

    The cuttlefish is colorblind. It has a single type of photoreceptor in its eye. It cannot distinguish colors. And yet it produces color matches that fool the color vision of its predators—di- and trichromatic fish that can see wavelengths the cuttlefish itself cannot perceive. This is the central paradox of cuttlefish camouflage, and after decades of research, science has gotten closer to understanding how it works without fully resolving the contradiction.

    The hardware

    The chromatophore system is, functionally, a neural display. Each chromatophore is a pixel. The brain is the graphics processor. The motor neurons are the data bus. Gilles Laurent at the Max Planck Institute for Brain Research described the research approach as “measuring the output of the brain simply and indirectly by imaging the pixels on the animal’s skin”—because each chromatophore’s expansion state reflects the firing rate of its controlling motor neurons, tracking chromatophores at high resolution is equivalent to tracking neural activity across tens of thousands of neurons simultaneously in a freely behaving animal.

    Laurent’s lab developed methods to track individual chromatophores at 60 frames per second, at single-cell resolution, over weeks of continuous observation as the animal breathed, moved, changed appearance, and grew. They could identify each chromatophore like a fingerprint—every animal’s arrangement is unique—and follow it even as new chromatophores appeared daily during development. By analyzing how chromatophores co-fluctuated—which ones expanded together, which ones were independent—they could infer the structure of the motor neuron populations controlling them, and from there, predict the organization of higher-level control circuits deeper in the brain. Reading the skin to reverse-engineer the brain.

    What they found overturned the assumption that cuttlefish camouflage patterns were simple. Traditional taxonomy divided cuttlefish patterns into three categories—uniform, mottled, and disruptive—with roughly 30 subcategories. The high-resolution tracking data revealed something far more complex: skin patterns are high-dimensional and dynamic, with the animal meandering through pattern space, accelerating and decelerating, sometimes producing nearly identical overall patterns using entirely different combinations of individual chromatophores. The skin display isn’t selecting from a fixed menu of preset patterns. It’s navigating a continuous space of possible configurations, course-correcting as it goes.

    A breakthrough finding reported in 2023 showed that cuttlefish undergo multiple color changes before settling on a camouflage pattern that matches their surroundings—a trial-and-error approach rather than the instantaneous, pre-programmed response the speed of the transformation seems to imply. The camouflage looks instant to the observer because the iterations happen within seconds. But the animal isn’t computing a perfect match and executing it. It’s generating candidates, evaluating them against what it sees, and converging on a solution. The distinction matters: it’s the difference between a lookup table and a search algorithm.

    The texture dimension

    Color and pattern alone don’t make a convincing disguise. A smooth-skinned animal on a bumpy coral surface still looks wrong, regardless of how well the colors match. Cuttlefish solved this by evolving papillae—muscular hydrostats in the skin that, when activated, produce three-dimensional bumps ranging from subtle texture changes to dramatic protrusions that mimic algae, coral, or rock surfaces. The papillae are controlled by a neural circuit separate from the chromatophore circuit—the two systems can be activated independently—but coordinated through shared brain regions so that color, pattern, and texture match simultaneously.

    A cuttlefish resting on a rocky substrate doesn’t just turn the right shade of brown. Its skin erupts into bumps that mimic the surface geometry of the rock. Move it to smooth sand and the papillae flatten, the chromatophores shift to a uniform sandy tone, and the animal becomes a patch of seabed. The transformation—color, pattern, luminance, texture—happens in less than a second.

    The colorblind problem

    Cuttlefish have a single visual pigment with peak sensitivity around 492 nanometers. One photoreceptor type means no color opponency—the neural comparison between different wavelength channels that enables color perception in animals with two or more photoreceptor types. By every definition used in visual neuroscience, the cuttlefish is monochromatic. It sees the world in shades of a single dimension.

    And yet: hyperspectral imaging studies—using cameras that record full-spectrum light data across every wavelength—have shown that cuttlefish camouflage provides high-fidelity color matches to natural substrates when evaluated through the visual systems of their fish predators. The spectral properties of cuttlefish skin and the substrates they match are often similar enough to fool trichromatic vision. The animal can’t see the colors it’s producing, and the colors it produces are right.

    How? The honest answer is that the mechanism isn’t fully understood, but several partial explanations have converged. First, the three chromatophore pigment classes and the underlying structural reflectors can, in combination, produce most colors found in marine environments through subtractive and additive mixing, without the animal needing to know what specific color it’s producing. Second, cuttlefish may be matching luminance—brightness—rather than hue, and getting the color right as a byproduct of getting the brightness pattern right. A 2024 study on octopus camouflage (a closely related cephalopod with the same single-photoreceptor constraint) found that they excel at matching background lightness but often miss color saturation, suggesting brightness matching is the primary computation and color match is a statistical bonus.

    Third—and this is where it gets genuinely strange—cuttlefish skin contains opsin proteins, the same light-sensitive molecules found in the retina. Researchers discovered opsin transcripts in the fin and ventral skin of the common cuttlefish. The skin opsins are identical to the retinal opsin, which means they can’t provide color discrimination (same single-pigment limitation), but they could provide local light-level sensing that allows the skin itself to contribute to the camouflage computation without routing all information through the eyes and brain. The skin might be sensing its own output and adjusting locally.

    In 2025, researchers at Scripps Institution of Oceanography genetically engineered soil bacteria to produce xanthommatin—the primary chromatophore pigment—at industrial scale, a thousandfold improvement over extraction from actual cephalopods. In 2024, scientists developed CHROMAS, a machine learning pipeline that tracks individual chromatophores frame by frame and quantifies how patterns emerge. The tools to finally crack the colorblind camouflage problem are arriving faster than at any point in the field’s history.

    Why it matters beyond marine biology

    The cuttlefish skin is, from an engineering perspective, a flexible, high-resolution, real-time display that changes color, pattern, and three-dimensional surface texture under direct neural control, powered by biological materials, operating at millisecond timescales, and doing all of this without the organism understanding color theory. Military researchers, materials scientists, and roboticists have been studying cephalopod camouflage for decades as a blueprint for adaptive materials—fabrics that change color, surfaces that alter texture, coatings that respond to their environment.

    But the deeper significance is neuroscientific. The cuttlefish skin is a window into the brain. Because each chromatophore is controlled by identified neurons, the skin pattern is a real-time, high-dimensional neural readout of the animal’s perceptual state. When a cuttlefish camouflages, its skin is displaying what its brain thinks the world looks like—a projection of its visual perception onto its own body surface. No other animal provides this kind of direct, externally visible readout of neural computation at the scale of tens of thousands of neurons simultaneously. The cuttlefish isn’t just hiding. It’s showing you what it sees.

    We cover cuttlefish camouflage alongside octopus distributed cognition, mirror neurons, and the full landscape of comparative neuroscience across our Neurozoology course—including why the most important display technology in neuroscience isn’t a screen in a lab. It’s the skin of a colorblind animal that paints what its brain perceives.