In a seawater tank at an aquarium in Japan, a jellyfish smaller than a pencil eraser is doing something no other complex animal is known to do. Turritopsis dohrnii, a hydrozoan from the Mediterranean about four millimetres across, has been injured by a researcher, and instead of dying it is collapsing inward — its bell folding, its tentacles retracting, its swimming muscles dissolving into a small blob of cells that will sink to the bottom of the tank, fasten itself to the glass, and grow back into the polyp stage it left behind when it was effectively a child. The same individuals have been observed doing this over and over again for years. The animal does not appear to age out of the trick.

The process is called transdifferentiation, and it is the reason Turritopsis dohrnii has been nicknamed the immortal jellyfish. The name overstates the case — the animal can still be eaten, crushed, or infected — but it is not metaphor. Under laboratory conditions, the jellyfish has been observed to reverse its own life cycle indefinitely, which makes it the only known multicellular animal with a built-in escape hatch from old age.

What the jellyfish actually does

Most jellyfish go through two main life stages. They start as a fertilised egg that develops into a larva, the larva settles on a hard surface and grows into a polyp — a small stalk with a mouth and tentacles, attached to rock or shell — and the polyp eventually buds off free-swimming medusae, the pulsing umbrella-shaped form most people picture when they hear the word jellyfish. The medusa reproduces sexually, releases eggs, and then dies. The arrow points one way.

Turritopsis dohrnii can run the arrow backwards. When the adult medusa is wounded, starved, or exposed to sudden changes in temperature or salinity, it does not simply repair itself. It dismantles. Its cells lose their specialised identities — muscle cells stop being muscle cells, nerve cells stop being nerve cells — and reorganise into a cyst-like ball that attaches to a substrate and grows into a new polyp colony. From there it can bud off fresh medusae again. The animal that comes out is genetically identical to the one that went in. It is, in the most literal biological sense, its own younger self.

This is what makes the case strange. Plenty of animals regenerate lost parts — salamanders regrow limbs, starfish regrow arms, certain flatworms can be sliced apart and reconstitute themselves. But regeneration replaces tissue. Transdifferentiation rewrites identity. A muscle cell in a regrowing salamander leg stays a muscle cell. In Turritopsis dohrnii, the muscle cell becomes something else entirely.

How it was discovered

The reversal was first noticed almost by accident. Observations of Turritopsis medusae in laboratory conditions showed that instead of dying after spawning, they were sinking to the bottom of containers and turning back into polyps.

The finding sat quietly in the literature for years until specialists began examining strange life cycles in hydrozoans. Among the cases discussed was the unusual jellyfish, and in carefully controlled experiments, researchers confirmed that the reversal was real, repeatable, and not a fluke of stressed captive animals. The developmental sequence was documented in detail, giving the species its odd new claim to fame.

Shin Kubota and the indefinite reboot

The person who has spent more time watching Turritopsis dohrnii reverse itself than anyone alive is Shin Kubota, who keeps colonies in Japan. Kubota has kept individual jellyfish through the cycle dozens of times. In one stretch he documented a single specimen rejuvenating ten times in two years, and the broader pattern in his tanks is that the reversal does not appear to degrade with repetition. The polyp that emerges from the twelfth cycle looks like the polyp that emerged from the first.

That is the part that startles biologists. Most cells that divide many times eventually accumulate damage — telomeres shorten, mutations build up, mitochondria misfire. The reset in Turritopsis dohrnii appears to clear something. Whether it clears everything, indefinitely, is still an open question, but no one has yet caught the animal failing at the trick under good conditions.

What the genome shows

In 2022, a team led by Maria Pascual-Torner and Carlos López-Otín at the University of Oviedo in Spain published the first complete genome of Turritopsis dohrnii alongside its close relative Turritopsis rubra, which cannot reverse its life cycle. The comparison was the point. The Oviedo team found that the immortal jellyfish carried expanded or duplicated copies of genes involved in DNA repair, telomere maintenance, the stem-cell pool, and the protective handling of damaged proteins. The species also carried variants in genes that govern cellular senescence — the state in which damaged cells stop dividing and start leaking inflammatory signals — that appear to make it easier for its cells to escape that state.

The picture that emerged was not a single magic gene but a combination. Turritopsis dohrnii appears to have stacked several different anti-aging adaptations that, taken together, give its adult cells the option of reprogramming themselves back to an earlier developmental state. Some of those same pathways are well-studied in humans. The Oviedo group was explicit that the animal is being studied as a model for human ageing, not because anyone expects to bottle its trick, but because the genes it leans on are the same genes that go wrong in our own cells when they wear out.

Why this does not mean immortality is solved

The leap from a four-millimetre hydrozoan to a human being is enormous, and the people who study Turritopsis dohrnii are the first to say so. The jellyfish has no brain, no organs in the vertebrate sense, no skeleton. Its body plan is a handful of cell types arranged in two thin layers. The challenge of reorganising those cells is closer to rearranging the same Lego pieces than to rebuilding a cathedral from rubble. Human cells, organised into tissues with long developmental histories and complex epigenetic memories, cannot simply be told to forget what they are and start over without losing the information that makes a person a person.

There is also a measurement problem. A review published in December 2025 in Genomic Psychiatry argued that the field’s standard tools for measuring biological age in any organism are deeply flawed, which means that even calling the jellyfish ageless requires care about what ageing is being measured against. The animal certainly resets developmental stage. Whether it resets every clock biologists care about is a harder claim.

And in the wild, Turritopsis dohrnii almost certainly does not live forever. It gets eaten by larger jellyfish, fish, sea slugs and sea anemones. It gets pulped by storms. It gets dragged in ballast water across oceans — the species has now been found everywhere from the Mediterranean to Japan to Panama to the coast of Florida, and the global spread is thought to be partly the work of shipping. The immortality is conditional. It works in still water and gentle hands.

The thing that stays with you

Other animals are now being looked at with new interest because of what was found in the laboratory. Comb jellies have been observed reverting from their adult form back to a larval one, suggesting that the trick may not be unique to a single species but rather an old, deeply buried capacity in animals with simple body plans. The hydra, a freshwater cousin of the jellyfish, has long been known to renew its cells continuously and shows few signs of ageing in the lab. The immortal jellyfish may turn out to be the most extreme example of a more general pattern rather than a one-off miracle.

Shin Kubota is now in his late sixties. He has written karaoke songs about the jellyfish he studies, performed them on Japanese television, and described the animal in interviews as the most miraculous creature on Earth. The jellyfish in his tanks, having gone through their cycles many times, will outlast him. Some of them will be the same individuals — biologically continuous with the polyps he first collected — long after the man who watched them reset is gone.

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The Ngogo chimpanzees of Kibale National Park in western Uganda have been continuously studied by primatologists for thirty years. The Ngogo Chimpanzee Project was co-founded in 1995 by John Mitani of the University of Michigan and David Watts of Yale University, and is now co-directed by Aaron Sandel of the University of Texas at Austin. The project has documented approximately 200 individual chimpanzees through their full life cycles, recorded their grooming networks, hunting parties, dominance hierarchies, and reproductive patterns, and produced one of the most detailed long-term datasets on chimpanzee social behaviour ever assembled.

The size of the community was, until quite recently, its most distinctive feature. Most wild chimpanzee communities contain approximately 50 individuals. The Ngogo community at its peak contained approximately 200, including more than 30 adult males, all of whom lived within a shared territory, recognised each other by sight and call, groomed each other, formed alliances and rivalries, mated across the community, and patrolled the boundaries of their shared range together against neighbouring groups.

The community was, on the available evidence, an exceptionally well-functioning chimpanzee society.

It is now in the middle of the second documented chimpanzee civil war in scientific history.

The day the split began

The collapse of the Ngogo community had a precise starting moment, which the long-term observation project happened to have a researcher on hand to witness. On the morning of 24 June 2015, Aaron Sandel was following a sub-group of Ngogo chimpanzees through the forest when the animals fell silent. Several of them began to grimace, a facial expression that in chimpanzees indicates nervousness or threat. Others began touching each other in patterns the researchers recognised as reassurance behaviour. In the distance, more chimpanzees could be heard approaching.

The normal pattern of Ngogo social life would have been for the two sub-groups to merge with each other, exchange the loud screaming, back-patting, and hand-holding greetings that chimpanzees use to reaffirm community membership, and then mingle freely for hours or days before separating again. This was the pattern Mitani and his colleagues had observed thousands of times across thirty years of fieldwork.

The pattern did not hold on the morning of 24 June 2015. As the approaching sub-group came into earshot, the chimpanzees with Sandel ran in the opposite direction. The approaching sub-group did not pursue them as a threat. The two sub-groups had, on the available behavioural evidence, simply decided not to meet.

From that morning, the social cohesion of the Ngogo community began to fray in measurable ways. Researchers tracked the network of grooming and association patterns and watched as individuals shifted into one of two emerging clusters, which the team came to call the Western and the Central groups. By 2017, the two groups had stopped using overlapping territory. By 2018, the deaths had begun.

The first killing

In January 2018, adult males from the Western group attacked and killed an adolescent male from the Central group named Errol. Sandel had watched Errol grow up. The pattern of the attack, in which five to ten adult males held the victim down while others bit, beat, and dragged him, was familiar to the researchers from previous documented cases of inter-community chimpanzee violence, in which Ngogo and other groups had attacked chimpanzees from rival neighbouring communities.

What was different about the killing of Errol was that the victim was not from a rival neighbouring community. He was from the same community that the attackers had been part of two and a half years earlier. The males who killed him had, in some cases, groomed his mother. They had patrolled the Ngogo territorial boundaries with him as members of the same hunting party. They had, on the long-term observational record, treated him as kin until the morning of 24 June 2015.

The killing of Errol established the pattern that has continued since. The 2026 paper in Science by Sandel and colleagues, titled “Lethal conflict after group fission in wild chimpanzees,” documents the period from 2018 to 2024, during which the Western group attacked and killed at least seven adult or adolescent males and seventeen infants from the Central group. An additional 14 Central males disappeared during the same period and were never recovered, although the team notes that some may have died from causes other than direct attack. The total number of killings since the data analysis ended in 2024 has continued to rise, with further attacks documented in 2025 and 2026.

All attacks since 2018 have been by the Western group against the Central group. The Central group, despite having been the larger of the two factions at the time of the split, has not retaliated in any documented case. The Western group, which started with 76 members, has grown to 108. The Central group is in stepwise decline.

Why this kind of event almost never happens

Inter-community violence between separate chimpanzee groups is well-documented in primatology. The Ngogo community itself has been one of the more aggressive communities ever studied, with documented attacks on chimpanzees from neighbouring communities going back to 1999. What is genuinely rare, and what makes the 2026 Sandel paper a significant scientific event, is for a single chimpanzee community to split into two factions and for those factions to then begin killing each other.

The Sandel team estimates, based on the rate at which such splits have been documented across all wild chimpanzee research sites combined, that a community fission of this kind occurs approximately once every 500 years per chimpanzee community. The team’s estimate is based on the only previous documented case, which is the chimpanzee war that Jane Goodall observed at Gombe Stream National Park in Tanzania between 1974 and 1978. In that case, the Kasakela community split into two factions, called Kasakela and Kahama, and over four years the Kasakela males systematically killed every adult male in the Kahama splinter group, eliminating it entirely as a community.

The Gombe War was, at the time, the most contested observation in primatology. Critics noted that Goodall had been provisioning the chimps with bananas at the research site since the 1960s, and argued that the artificial food supply had created unnatural competition that produced the violence. The Gombe War, on this critique, was an artefact of human interference rather than a natural feature of chimpanzee behaviour.

The Ngogo civil war substantially weakens this critique. The Ngogo Chimpanzee Project has never provisioned the chimps with food, and the violence has unfolded entirely without human food interference, as the University of Michigan press release accompanying the Science paper notes. The behaviour Sandel and his colleagues have documented is, on the strongest current reading of the evidence, a natural feature of chimpanzee social biology that emerges under specific conditions, not an artefact of human intervention.

Why did they turn on each other

The 2026 Sandel paper does not identify a single cause for the Ngogo split. The team examined several factors that may have contributed, all of which appear to have operated in combination rather than individually.

The first was the unusual size of the Ngogo community. At approximately 200 individuals and more than 30 adult males, the group was approximately four times the size of a typical wild chimpanzee community. Chimpanzee social cohesion is maintained by individual relationships of grooming, alliance, and recognition, and there appear to be limits to how many such relationships any one chimpanzee can sustain. The Ngogo community had, on the available behavioural evidence, grown beyond the size at which its members could maintain personal bonds with every other member, and had been operating for at least a decade with internal sub-structures that the researchers called clusters.

The second was the deaths of several well-connected adult males in the years immediately before the 2015 split. The Sandel team identifies five adult males who had served as social bridges between the Western and Central clusters and who died of natural causes between approximately 2010 and 2014. The loss of these individuals appears to have weakened the connections that held the two emerging factions together.

The third was a change in the dominance hierarchy. A new alpha male emerged in 2015, an event that in chimpanzee communities typically occurs every six to eight years and produces measurable increases in aggression and social tension during the transition period.

The fourth was a respiratory epidemic in 2017, traced to a human-origin pathogen, which killed approximately 25 Ngogo chimpanzees and removed additional social links between the two emerging clusters.

None of these factors, individually, would have been sufficient to fracture a chimpanzee community. The Sandel team’s central interpretation is that the combination of large group size, the loss of social bridge individuals, the alpha male transition, and the epidemic produced a network of social relationships that became too thin to hold the two clusters together. When the relationships broke down, the underlying behavioural capacity for inter-community violence, which Ngogo chimpanzees had previously directed against rival neighbouring groups, was redirected inward against former members of their own community.

The honest limitations

Several caveats apply to the interpretation above.

The first is that the Ngogo civil war is still in progress. The 2026 Science paper covers data through 2024, but additional killings have been documented in 2025 and 2026, and the long-term outcome of the conflict is not yet settled. The Central group may eventually be eliminated, as the Kahama group was at Gombe, or it may stabilise as a smaller community, or it may recover and re-establish itself. The current trajectory points toward continued decline, but the time horizon is genuinely uncertain.

The second is that the proposed causes of the split are, at this stage, contributing factors rather than established triggers. The Sandel team has documented the conditions under which the split occurred, but the specific reason that the community fractured rather than continuing in its previous arrangement is not yet known. Multiple chimpanzee communities have grown to large sizes, lost social bridge individuals, transitioned to new alpha males, and survived epidemics, without fracturing in this way. What made Ngogo different is genuinely an open scientific question.

The third is that the implications for human conflict, which several commentators on the 2026 paper have drawn, should be treated with caution. Chimpanzees and humans share a common ancestor approximately six million years in the past, and there are clear evolutionary continuities in patterns of aggression, alliance, and intergroup conflict. The specific dynamics of human civil wars, which involve ideology, ethnic identity, political institutions, and material resources at scales that have no chimpanzee equivalent, are not directly modelled by the Ngogo conflict.

What it means

Several things follow from the Ngogo civil war evidence that are worth saying clearly.

The first is that the behavioural capacity for what humans call civil war, in which a previously unified social group fractures into factions that then attempt to destroy each other, is not, on the available evidence, unique to humans. It has now been documented twice in chimpanzees, in two separate national parks, in two separate countries, separated by four decades and the entire breadth of the African continent. The behaviour is rare but it is reliably reproducible under the right conditions, and those conditions appear to be specific features of chimpanzee social biology rather than anything imposed by human contact.

The second is that the underlying mechanism, on the strongest current reading of the evidence, is the breakdown of personal relationships within a social group that has grown beyond the scale at which such relationships can be maintained. The Ngogo community was at approximately four times the size of a typical chimpanzee community. The relationships that held it together were stretched thin even before the deaths and the epidemic that further weakened them. The split occurred along the fault line of the two pre-existing clusters within the community, which had been visible to researchers as internal structures for at least a decade before the rupture.

The third is that the violence, once the social break occurred, was directed by Ngogo chimpanzees against animals they had previously treated as kin. The Western males who killed Errol in January 2018 had groomed his mother. They had patrolled the Ngogo territorial boundaries with him as members of the same hunting party. They had, by every available behavioural measure, considered him a member of their own community until the morning of 24 June 2015. The behavioural capacity to redefine former community members as legitimate targets of lethal aggression appears, on the available chimpanzee evidence, to be substantially older than the evolution of language, ideology, or the human capacity for ethnic identity formation.

The fourth, on the strongest current reading of the peer-reviewed evidence, is that the question Aaron Sandel has been asking since the morning of 24 June 2015, which is what makes a stable social group come apart and what makes its former members turn on each other, is not just a question about chimpanzees.

The Ngogo community had been stable for thirty years.

It came apart on a single morning, in a way that no one was expecting, and the killings began three years later.

The chimpanzees are still attacking each other.

The post Chimpanzees at war for eight years in Uganda’s Kibale National Park have, since 2018, systematically killed at least 28 members of their own former community in coordinated raids, in what a 2026 peer-reviewed paper in Science has described as only the second documented chimpanzee civil war in history, in a community that until 2015 had been the largest cohesive group of wild chimpanzees ever recorded appeared first on Space Daily.