As glaciers melted and the seas rose after the most recent ice age, the last surviving woolly mammoths were crowded onto small, isolated northern islands, where they stayed for millennia before joining their mainland cousins in oblivion. 
 
 Now there is evidence that water problems — the lack of clean fresh water — is what finally killed off the remnant population of woolly mammoths that took refuge on a Bering Sea island off Western Alaska. 
 
 A new study published in the Proceedings of the National Academy of Sciences uses chemical analysis of sediment below a lake on St. Paul Island to reconstruct conditions that appear to have killed off some of the world's last woolly mammoths. 
 
 The animals survived on St. Paul until about 5,600 years ago, about 5,000 years after most of the world's mammoth populations disappeared from the grasslands of North America and Eurasia. But even on the isolated Bering Sea refuge, conditions for woolly mammoths were deteriorating. As seawater levels rose and shrank the island's size, the climate became warmer and drier. The island's freshwater resources shriveled and the remnant woolly mammoths suffered, the study found. 
 
 "Freshwater resources look like the smoking gun for what pushed them into this untenable situation," study co-author Matthew Wooller, director of the Alaska Stable Isotope Facility at the University of Alaska Fairbanks, said in a statement released by UAF. 
 
 The study, the work of a large international team, uses analysis of a sediment core taken in March 2013 from the bed of Lake Hill, one of St. Paul's few lakes. The analysis of magnetic qualities, oxygen isotopes and assemblages of the remains of tiny aquatic creatures that lived there showed how freshwater became scarce between 7,850 and 5,600 years ago. It also uses isotope analysis of mammoth bones and teeth that showed the animals were showing stress from progressively drier conditions. 
 
 Dehydration and heat stress likely finished off the island's mammoths, which could not move to better territory, said Russ Graham, a Penn State University paleontologist and the study's lead author. Modern elephants can consume more than 50 gallons a day, and mammoths also needed lots of water to cool their huge bodies, Graham said in an email. "This would have been particularly hard for woolly mammoths because they have evolved adaptations like specific hair types to keep them warm in the cold climates. This would have been a maladaptation for warmer climates," he said. 
 
 As lakes became shallower, the water in them became cloudier and dirtier — the types of water conditions that modern elephants dislike and avoid, the paper notes. Evaporation caused minerals to be more concentrated in the water that remained, Wooller said. 
 
 "In essence the lake water was becoming more saline — although not as a result of mixing with ocean water but rather as a result of concentrating of minerals in the lake as lake levels dropped," he said in an email. 
 
 The mammoths probably contributed to their own demise, the study says, by digging into the earth — in the manner of modern elephants that dig lakeside mini-wells — and stripping away plant cover edging the lakes and speeding up the erosion that was diminishing water quality. 
 
 The extinction of St. Paul's remnant woolly mammoth has long been a puzzle. 
 
 What ultimately killed them was probably not hunting, the authors of the new paper have concluded. There is no evidence than humans used St. Paul Island before the arrival of Russians in the late 18th century, 
 
 Predation from polar bears was not to blame either, as the oldest polar bear remains found on the island are at least 1,000 years more recent than the most recent mammoth remains, the study points out. 
 
 Increasing snowpack has been posed as a possible extinction driver, but that theory is "inconsistent" with the isotope analysis of the lakebed sediments. Volcanic eruptions are also ruled out. And it is unlikely that extinction came from shifts in the types of plants growing on the island because the vegetation types were stable during the Holocene epoch — the recent past by geologic measure — though analysis of pollen suggests that tundra productivity might have been declining, the study said. 
 
 By evidence and deduction, that leaves the scarcity of freshwater as the most likely culprit. 
 
 The St. Paul mammoths' fate sends some important messages about modern climate change, the authors said. 
 
 Island populations are especially vulnerable to environmental changes, even small ones, and the study "underscores the need to pay particular attention to islands in an environmentally changing world," Graham said. 
 
 Freshwater supplies on islands are also very vulnerable, he said. People living on some South Pacific islands are already facing some freshwater shortages. As the sea rises, the wedge of saltwater has been pressing up against the freshwater in the water table, restricting it, he said. 
 
 St. Paul was not the only island where woolly mammoths found refuge after most of their kind had been wiped out. 
 
 The world's last known surviving woolly mammoths lived on Russia's Wrangel Island, now a nature reserve. Mammoths lived there until about 3,700 years ago, according to paleontological evidence. ||||| Bones and teeth belonging to the ancestors of the short-statured human lineage known as “the Hobbits” have been discovered on the Indonesian island of Flores. The fossils, which date back 700,000 years, are offering fresh insights into the origin of this mysterious species. 
 
 In two new papers in Nature, researchers from Australia’s University of Wollongong describe the fossilized remains of three small-bodied hominins thought to be the distant ancestors of Homo floresiensis, an extinct species of ancient human popularly known as the “Hobbits.” The fossils, which include an adult mandible and several teeth, are the first skeletal remains to be discovered on the Indonesian island of Flores outside of Liang Bua—the cave in which paleoanthropologists discovered the original Hobbit remains. 
 
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 These ancient humans were brought to the world’s attention when the remains of a single adult individual—who would have stood a mere 3½ feet tall—were discovered on Flores in 2003. Since then, another nine specimens have been recovered, including one complete skull. These remains date back to between 95,000 and 50,000 years ago and belong to an entirely new species of nascent humans, one dubbed Homo floresiensis. 
 
 Scientists have speculated that their miniaturized characteristics were the result of insular dwarfism, which happens to animals that have become isolated on small islands with limited access to food. This evolutionary process caused the bodies and brains of these early humans to shrink down in size, but they retained their ability to stand upright and use basic stone tools. 
 
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 “Human diversity was far greater than we ever realized.” 
 
 The precise origin of these Hobbit-like humans remains a mystery. One theory is that these individuals evolved from an isolated population of large-bodied Homo erectus, and then dwarfed over time. The second theory is that these early humans were descended from another member of our genus, such as Homo habilis. Complicating matters further is the suggestion that they’re not a distinct species at all, and that these individuals were suffering from some sort of congenital disease that caused their short stature. 
 
 Based on a morphological analysis of the new fossils, it now appears that these so-called Hobbits were in fact descended from H. erectus. About a million years ago, a band of these early humans got stuck on the island of Flores. Then, over the next 300,000 years, they gradually dwarfed in size, living on the island’s savannah-like grasslands alongside elephants, rats, and Komodo dragons until their mysterious disappearance some 50,000 years ago. 
 
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 The new fossils were uncovered by Gerrit van den Bergh and his colleagues in 2014, after the researchers performed a series of test excavations to identify which stratigraphic layer was most likely to yield the remains. 
 
 “This find...quashes once and for all any doubters that believe Homo floresiensis was merely a sick modern human.” 
 
 The fossils, which include an adult lower right jaw fragment and several teeth, were found in layers of sedimentary rock at a site called Mata Menge. These finds pre-date the bones discovered at Liang Bua by more than half a million years, dramatically extending the timeline of the Hobbits on Flores. Using several dating techniques, the researchers say the fossils are about 700,000 years old. The recent discovery of one million-year-old stone tools pushes back their time on the island even further (unless, of course, these tools were made by some other group of humans). 
 
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 “This find has important implications for our understanding of early human dispersal and evolution in the region and quashes once and for all any doubters that believe Homo floresiensis was merely a sick modern human,” said van den Bergh. “Human diversity was far greater than we ever realized.” 
 
 Interestingly, the adult individual was about two-thirds the size of later Hobbits, which means these ancestors were either equal to or smaller than their descendents. That means these insular humans obtained their small stature in just 300,000 years. That may sound like a long time, but it’s not much in evolutionary terms. The process of insular dwarfism, it would appear, works quickly. 
 
 
 
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 How a group of full-bodied H. erectus made their way to the remote island of Flores remains a matter of speculation. These early humans, who could just barely forge stone tools by smashing them together, couldn’t possibly have had the technological capacity to make boats. Speaking at a press conference yesterday, van den Bergh said they might have been swept to the island by a tsunami, where they remained marooned and isolated. This region is known for volcanic and tectonic activity. What’s more, the 2004 Indian Ocean earthquake and tsunami swept individuals out into the sea as far as 38 miles—including a woman who was seven weeks pregnant, and later rescued. 
 
 Another possibility is that this newly found lineage pre-dates the first hominin arrival on Flores, and that it wasn’t H. erectus that got stranded on the island. This would mean that some immediate group of hominin ancestors came through the north from Asia, possibly via Sulawesi. 
 
 “That’s another hypothesis that we have to keep in mind,” said van den Bergh. 
 
 [Nature 1, 2] ||||| iStock/Getty Images Plus 
 
 Isolated on an island in the Arctic Ocean, not only were woolly mammoths the last of a dying species but they were also swamped with ‘bad genes’ that are likely to have stripped their sense of smell and saddled them with translucent coats. 
 
 A study1 published 2 March in PLOS Genetics gives a rare insight into how genomes change as a species dies out. Towards the end of the last Ice Age, around 11,700 years ago, woolly mammoths ranged through Siberia and into the colder stretches of North America. But by about 4,000 years ago, mainland mammoths had died out and only 300 remained on Wrangel Island off the Siberian coast. 
 
 In order to examine this disappearance at the genetic level, biologists Rebekah Rogers and Montgomery Slatkin at the University of California, Berkeley, compared the complete genome of a mainland mammoth (Mammuthus primigenius) that lived about 45,000 years ago with that of a Wrangel Island mammoth from about 4,300 years ago. The sequences were made available by Love Dalén at the Swedish Museum of Natural History in Stockholm. 
 
 “As I looked at the sequence data,” says Rogers, “it became very clear that the Wrangel mammoth had an excess of what looked like bad mutations.” 
 
 
 
 Some of these changes are only visible to a geneticist’s eye. Compared with the mainland mammoth, the Wrangel Island specimen's genome was riddled with deletions and an abundance of sequences called stop codons — which tell a cell when to stop transcribing a section of DNA — among other changes to the DNA. But some of these changes would also have been visible in the mammoth’s behaviour and appearance. 
 
 
 
 Rogers and Slatkin found that genes related to smell and urinary proteins, which in modern elephants are important for eliciting mating behaviours or signalling social status were shut down by the mutations. These might be related, the researchers hypothesize, because a duller sense of smell may have been hitched in a feedback loop to the loss of urinary proteins, leading to the rapid loss of both. Changes to the Wrangel mammoths’ coats would have been even more obvious. Rogers and Slatkin propose that a mutation in a part of the genome called FOXQ1 would have given the mammoths a ‘satin’ coat, marked by fur that is the same colour as normal but is shiny and translucent. 
 
 Reduced competition 
 
 What happened on Wrangel wasn’t a matter of inbreeding, Rogers says — the genetic signal is different. 
 
 “What did happen was that the population was simply small,” she says, and “under these circumstances any mammoth was better than no mammoth at all”, so natural selection did not operate in the usual way. This allowed unhelpful mutations to rack up, following a previously identified phenomenon called nearly neutral genome evolution. “Bad mutations that would normally be weeded out weren’t removed from the population because of reduced competition,” says Rogers. 
 
 “Isolation and reducing population size have long been recognized as important factors causing endangerment,” says palaeontologist Ross MacPhee of the American Museum of Natural History in New York City, but the recognition of the mammoth’s “genetic meltdown” is a sign of how far studies of ancient DNA have come, and the work that still lies ahead. 
 
 The changes on Wrangel Island took place after mammoths had already been wiped out on the mainland. Tracking the downfall of the species is an ongoing effort, says MacPhee. “With additional specimens, drawn from other times and parts of the woolly mammoths’ enormous range, we may get a better picture of the genetic load that this species was labouring under at the end of its tenure.” 
 
 Still, MacPhee adds, the study “is maybe telling us something very important about what happens in populations already under severe threat because of diminished range and numbers”. 
 
 Endangered mammals 
 
 MacPhee cautions that no single animal or genome can tell the whole story for an entire species. But he notes that human hunting, climate change or any other external factor wasn't enough by itself to wipe out the woolly mammoth. There had to be some other element operating within the animals, driving them to extinction. 
 
 As dramatic as genetic meltdown sounds, Rogers says that it’s difficult to tell whether the increase in bad mutations contributed directly to the final extinction of the woolly mammoth. Yet the findings have implications for the survival of the mammoths’ elephant cousins and other endangered mammals. Rogers notes that it’s better to prevent a species from becoming endangered in the first place than to try to recover its genetic diversity after a sharp plummet. 
 
 “Even though we can improve the number of individuals in endangered populations,” she says, “their genomes may still bear the hallmarks of genomic meltdown, which will be difficult to undo.”
– A "mini-mammoth" the size of a baby elephant has been identified on the island of Crete. Mammuthus creticus is the tiniest mammoth ever found, and is another example of "dwarfism" on islands, where scare resources can keep animals small, notes the Telegraph. Fossilized teeth of the three-foot-tall mammoth were first discovered in 1904, but were initially believed to be elephant teeth. Scientists only recently re-examined them and determined they were evidence of a miniature mammoth. They also returned to the spot in Crete and discovered a mini leg bone. "Dwarfism is a well-known evolutionary response of large mammals to island environments," said lead researcher Victoria Herrige from London's Natural History Museum. "Our findings show that on Crete, island dwarfism occurred to an extreme degree, producing the smallest mammoth known so far." Researchers believe the animals may have evolved from regular-sized mammoths as long as 3.5 million years ago.