Several species alive today exist as just one or two known individuals, and a handful more survive only as single-digit populations teetering at the edge of disappearance. The most famous current example is the northern white rhinoceros, reduced to two living females, neither of which can reproduce naturally. But the concept of “one left” stretches across the animal and plant kingdoms, from a lone tree on a remote New Zealand island to softshell turtles in Vietnamese lakes. These last survivors, sometimes called endlings, occupy a strange space in conservation: biologically present but ecologically already gone.
The Northern White Rhino
The northern white rhinoceros is probably the most widely recognized species down to its final individuals. Only two remain: Najin and her daughter Fatu, both living under armed guard at the Ol Pejeta Conservancy in Kenya. Neither female can carry a pregnancy to term due to health problems, which makes the subspecies functionally extinct even though living members still exist.1PubMed Central. Genomic map of the functionally extinct northern white rhinoceros (Ceratotherium simum cottoni) The last male, a bull named Sudan, was euthanized in 2018 after age-related health complications, leaving the two females as the sole representatives of a lineage that once roamed across central and eastern Africa.2Veterinary Record. Can IVF save the northern white rhino from extinction?
What makes the northern white rhino case unusual is that scientists had some warning. Poaching for horn, driven by demand in traditional medicine markets, collapsed the wild population over the course of a few decades. By the time intensive conservation kicked in, the numbers were already too low. The term “functionally extinct” captures this reality: the species is not technically gone, but it has lost the ability to sustain itself through natural reproduction.3PubMed. Progress Toward Genetic Rescue of the Northern White Rhinoceros (Ceratotherium simum cottoni)
Lonesome George and the Idea of the Endling
Before the northern white rhino became the poster species for “last of its kind,” that role belonged to Lonesome George, a Pinta Island giant tortoise from the Galápagos. George was discovered in 1971 and spent decades at the Charles Darwin Research Station as the only known purebred member of Chelonoidis abingdoni. When he died in June 2012, the subspecies was declared extinct. His death marked the loss of one of ten surviving giant tortoise species from the Galápagos Archipelago.4Biological Conservation. The genetic legacy of Lonesome George survives: Giant tortoises with Pinta Island ancestry identified in Galápagos
George’s story resonated far beyond the scientific community because it was so personal. He was a single animal, identifiable and named, carrying an entire evolutionary lineage on his shell. Repeated attempts to breed him with females of closely related species failed. The word “endling,” coined in the 1990s, describes exactly this situation: the last known individual of a species or subspecies. George became the textbook example. But his genetic story had a twist. After his death, researchers surveyed tortoises on the nearby volcano of Isabela Island and found individuals carrying partial Pinta Island ancestry, likely descendants of tortoises moved between islands by whalers or pirates centuries ago.4Biological Conservation. The genetic legacy of Lonesome George survives: Giant tortoises with Pinta Island ancestry identified in Galápagos The pure lineage was gone, but fragments of its DNA persisted in hybrids. That bittersweet finding highlights a recurring theme: extinction is not always a clean boundary.
Plants Can Be Endlings Too
When people think about the “last of a species,” they almost always picture an animal. But some of the most extreme cases are plants. Pennantia baylisiana, a small tree native to the Three Kings Islands off northern New Zealand, was long known from a single wild individual. That lone tree was female, and since the species was thought to be dioecious (needing separate male and female plants to reproduce), the situation looked hopeless. A seedling eventually grew from one of its seeds, which threw the whole understanding into question. Researchers suggested the seedling may have arisen through normal sexual processes, casting doubt on whether the species truly requires a separate male tree to set viable seed.5New Zealand Journal of Botany. The breeding system of Pennantia baylisiana (Icacinaceae) Cuttings and propagated plants now exist in botanical gardens, but the wild population remains effectively a single individual.
Wood’s cycad (Encephalartos woodii) is an even more striking case. This South African cycad is known from a single male clone. It was first collected from a forest in KwaZulu-Natal in 1895, and despite extensive searches, no female has ever been found in the wild. Every specimen alive today, scattered across botanical gardens worldwide, is a genetic copy of that one original male. Without a female, sexual reproduction is impossible. Some researchers have explored pollinating closely related cycad species with E. woodii pollen and then backcrossing offspring over multiple generations to approach the original genome, but this is a slow process measured in decades per generation. Wood’s cycad is, in a sense, the loneliest plant on Earth: an entire species that is also a single individual, endlessly cloned but never reproducing.
Other Animals on the Edge
The Yangtze giant softshell turtle (Rafetus swinhoei) has hovered at the brink for years. Once found across parts of China and Vietnam, the species was reduced to a handful of confirmed individuals by the early 2000s. The last known female at the Suzhou Zoo in China died during an artificial insemination attempt in 2019. At least one wild individual was identified in a Vietnamese lake in recent years, but with no confirmed breeding pair, the species’ future is grim. The situation is complicated by the fact that these turtles are extremely cryptic, spending most of their lives submerged in murky water, so undetected individuals could theoretically exist. But “could theoretically exist” is not the same as “exist,” and each passing year without a confirmed sighting makes the odds worse.
The vaquita, a tiny porpoise endemic to the northern Gulf of California in Mexico, represents another version of this story. While not literally down to one individual, population estimates in recent years have placed the species at roughly ten animals, and possibly fewer. Entanglement in illegal gillnets set for another endangered fish, the totoaba, is the primary cause of decline. Conservation efforts have been intense, including attempts to physically remove nets from the vaquita’s habitat, but the population has continued to shrink. The vaquita may not be an endling yet, but it illustrates how quickly a species can approach that threshold when threats are not eliminated.
Functional Extinction Versus Absolute Extinction
The northern white rhino is alive but functionally extinct. Lonesome George was alive and then absolutely extinct. The distinction matters for conservation priorities. A functionally extinct species still has living tissue, and that means it still has usable DNA, potentially viable cells, and a window for technological intervention. An absolutely extinct species has none of those things, unless someone had the foresight to freeze samples beforehand.
Functional extinction can also apply to populations that are technically large enough to count but too small, too old, or too genetically depleted to recover. A group of twenty elderly individuals of a long-lived species, all past reproductive age, is functionally extinct. So is a population that has lost so much genetic diversity that inbreeding depression makes each successive generation weaker. The concept is not about a magic number but about whether the biological capacity for self-sustaining reproduction still exists.
How Scientists Know Whether Anyone Is Really Left
Declaring a species extinct is surprisingly difficult. Absence of evidence is not evidence of absence, especially for species that are small, secretive, or live in hard-to-survey habitats. This is where environmental DNA, or eDNA, has become a game-changer. Instead of needing to physically spot an animal, researchers can collect water or soil samples and test them for genetic traces. A study comparing survey methods for the eastern indigo snake found that pairing traditional visual surveys with eDNA sampling was the most cost-effective way to reach a high probability of detection.6Journal for Nature Conservation. Comparison of camera traps, eDNA, and visual encounter surveys for threatened species detection
For species that live in burrows or underground water systems, eDNA can be particularly valuable. Researchers working with a critically endangered Australian burrowing crayfish (Engaewa pseudoreducta) developed a genetic test that could detect the species from soil pellets expelled from burrow entrances, eliminating the need to dig up burrows and destroy habitat just to confirm the crayfish was there.7Environmental DNA. Testing multiple environmental DNA substrates for detection of the cryptic and Critically Endangered burrowing freshwater crayfish Engaewa pseudoreducta For aquatic species, CRISPR-based tools have pushed sensitivity even further. A detection assay developed for the endangered delta smelt, a fish in California’s San Francisco Estuary, could pick up as few as three copies of the species’ DNA per reaction, a dramatic improvement over earlier methods.8Environmental DNA. CRISPR‐based environmental DNA detection for a rare endangered estuarine species
These technologies matter for endling situations because they help resolve the agonizing question of whether undetected individuals remain. A single confirmed detection from an eDNA sample can rewrite a species’ status from “probably extinct” to “still hanging on.” Conversely, years of negative eDNA results across a species’ known range can lend confidence to an extinction declaration.
Frozen Zoos and Stem Cell Rescue
When a species drops to its last few individuals, conventional breeding programs are no longer enough. This is where biobanking and stem cell technology enter the picture. The Frozen Zoo at the San Diego Zoo Wildlife Alliance, for example, holds cryopreserved cells from over a thousand species. For the northern white rhino, researchers have generated induced pluripotent stem cells (iPSCs) from skin samples stored in such biobanks, including cells from nine genetically diverse northern white rhinos and two southern white rhinos. The goal is to eventually coax these stem cells into becoming functional egg and sperm cells that could be used for in vitro fertilization.9PubMed Central. Rewinding Extinction in the Northern White Rhinoceros: Genetically Diverse Induced Pluripotent Stem Cell Bank for Genetic Rescue
The science is advancing on multiple fronts. Researchers have made progress differentiating iPSCs into functional gametes and even into blastoid structures that mimic early embryos, which could bypass the need for donor eggs entirely.10PubMed Central. Application of induced pluripotent stem cells in the conservation of endangered animals Cryopreservation is the linchpin of all of this: by freezing viable cells from individuals that are now dead, scientists create a genetic time capsule. Sperm collected from Sudan before his death, for instance, has already been used to create embryos via IVF with eggs harvested from Fatu. Those embryos have been implanted in surrogate southern white rhino females, though as of mid-2025 a live birth has not yet been confirmed.11PubMed. The ART of bringing extinction to a freeze – History and future of species conservation, exemplified by rhinos
This kind of work is expensive, technically demanding, and far from guaranteed. But it represents a fundamental shift in what “extinct” means. A species with zero living members but a well-stocked biobank is in a different category than one that vanished without a trace. The question of whether creating an animal in a lab from frozen cells truly counts as “saving a species” is philosophically thorny, but practically, it keeps options open.
When Rarity Itself Becomes the Threat
One of the cruelest dynamics in conservation is that the rarer a species becomes, the more valuable it can become to collectors, poachers, and the exotic wildlife trade. Researchers have described this as the anthropogenic Allee effect: humans place exaggerated value on rarity, which fuels disproportionate exploitation of rare species, making them rarer still and thus even more desirable, creating a feedback loop that can drive a species to extinction.12PubMed Central. Rarity value and species extinction: the anthropogenic Allee effect
This is not just a theoretical model. The price-rarity relationship has been documented across wildlife markets, where prices for rare species’ products climb as populations decline, creating financial incentives to harvest the very last individuals even when search costs are high.13PubMed. High prices for rare species can drive large populations extinct: the anthropogenic Allee effect revisited Rhino horn is the obvious example, but the same pattern appears in the orchid trade, rare bird egg collecting, and the market for exotic reptiles. Mathematical models show that this dynamic can push even relatively large populations toward extinction if the price premium for rarity is steep enough.14Natural Resource Modeling. MODELING THE EFFECT OF RARITY VALUE ON THE EXPLOITATION OF A WILDLIFE SPECIES SUBJECTED TO THE ALLEE EFFECT For a species already down to a handful of individuals, the effect is devastating: the last survivors are precisely the ones with the highest price on their heads.
What Disappears Along with the Last Individual
When a species goes extinct, it does not vanish alone. Every organism exists in a web of relationships with parasites, mutualists, and dependent species. Researchers have argued that the loss of a host species can trigger cascading coextinctions across food webs, and that these secondary losses may be most severe in parasitic and mutualistic relationships.15PubMed Central. The sixth mass coextinction: are most endangered species parasites and mutualists? A specialized pollinator that depends on a single plant species goes extinct when the plant does. A parasite that can only complete its life cycle in one host disappears with that host. The endling, in its final days, is carrying not just its own lineage but potentially the last members of several other lineages that nobody ever catalogued.
This is one of the less visible dimensions of the endling problem. Conservation attention, funding, and public sympathy tend to concentrate on the charismatic last animal, the George or the Sudan. Meanwhile, the unnamed mites, nematodes, and fungi that evolved alongside that species over millions of years slip away unrecorded. Some researchers estimate that for every well-known species extinction, multiple dependent species are lost as well. The total cost of an endling dying is almost certainly larger than the loss of a single species.
Rediscoveries and the Lazarus Effect
Not every species declared lost actually stays lost. The phenomenon of rediscovering species thought to be extinct, sometimes called the Lazarus effect, happens more often than you might expect. Senecio reitzianus, a plant from sand dunes in southern Brazil, was described from a single specimen and known only from that original collection for nearly seventy years. Researchers then found a living population about 20 kilometers from the original site.16Phytotaxa. Rediscovery of Senecio reitzianus (Asteraceae), a species believed to be possibly extinct, on Santa Catarina Island, southern Brazil
Similar stories have played out with animals. The coelacanth, a fish thought to have been extinct for 65 million years, turned up in a South African fish market in 1938. The black-footed ferret, declared extinct in the wild in 1987, was rediscovered and became the subject of one of the most intensive captive breeding programs in history. These cases serve as reminders that our knowledge of what still exists in remote forests, deep oceans, and unexplored cave systems is incomplete. They also complicate the endling concept: if you believe you are looking at the last individual but a small hidden population persists somewhere, the species was never truly down to one. The problem is that you rarely know this at the time.
The First De-Extinction
In 2003, scientists achieved something that had never been done before: they cloned an extinct animal. The Pyrenean ibex, a subspecies of wild goat that went extinct in 2000 when the last female, named Celia, died in northern Spain, was briefly brought back using nuclear transfer. Researchers had preserved skin samples from Celia before her death, and they used those cells to create embryos that were implanted in domestic goat surrogates. One kid was born alive but died within minutes due to a lung defect.17PubMed. Revival of extinct species using nuclear transfer: hope for the mammoth, true for the Pyrenean ibex, but is it time for “conservation cloning”?
The Pyrenean ibex experiment was both a proof of concept and a cautionary tale. It showed that cloning from preserved tissue is technically possible, but it also showed how fragile the process remains. The cloned kid was genetically identical to Celia, meaning that even a successful clone would have produced a population of one, no more genetically diverse than the endling it was copied from. For cloning to meaningfully rescue a species, you need preserved material from multiple genetically distinct individuals, which loops back to the importance of biobanks and frozen tissue collections. The ibex case illustrated that by the time a species reaches its last individual, the opportunity for genetic rescue has usually already passed unless someone started collecting samples much earlier.
Why Some Species Get Saved and Others Do Not
Conservation resources are finite, and the species that get the most attention tend to be large, charismatic, and mammalian. The northern white rhino receives millions of dollars in research funding. Wood’s cycad gets a fraction of that. The burrowing crayfish Engaewa pseudoreducta, critically endangered and living in a handful of wetlands in Western Australia, gets even less. The eDNA tools being developed to detect it are partly motivated by the fact that traditional surveys, which involve digging up its burrows, destroy the very habitat being protected.7Environmental DNA. Testing multiple environmental DNA substrates for detection of the cryptic and Critically Endangered burrowing freshwater crayfish Engaewa pseudoreducta
The uneven distribution of conservation attention means that many species become endlings without anyone noticing. Invertebrates, fungi, and small plants make up the vast majority of biodiversity, but they rarely get named, monitored, or mourned. A species of beetle that lived on a single mountain ridge and disappeared when that ridge was logged is just as extinct as Lonesome George, but it never had a name in the public imagination. The endlings we know about are almost certainly a tiny fraction of the endlings that have existed.
This asymmetry shapes what we think extinction looks like. The iconic image of the lone rhino in a guarded enclosure or the ancient tortoise in a research station is real, but it represents the lucky cases: species that at least had humans trying to save them. The more common endling story is one that no one documented at all.