(CNN) Our ancestors learned to respect the auroch, and immortalized them in pre-historic cave paintings. 
 
 The earliest cows were mighty beasts that stood almost as tall as elephants, with lean, powerful frames and fearsome horns that would make a hunter think twice. 
 
 For thousands of years the aurochs were the largest land mammals in Europe, until the rise of human civilization decimated their numbers, and the last of the species died in Poland in 1627 -- one of the first recorded cases of extinction. 
 
 Conservationists now believe the loss of the keystone herbivore was tragic for biodiversity in Europe, arguing that the aurochs' huge appetite for grazing provided a natural "gardening service" that maintained landscapes and created the conditions for other species to thrive. 
 
 The theory is now being put to the test, as a "near 100% substitute" of the beast is returned to the forests. 
 
 Cave painting in Lascaux, France dating back around 17,000 years which is believed to depict an auroch. 
 
 Speed breeding 
 
 Ecologist Ronald Goderie launched the Tauros programme in 2008, seeking to address failing ecosystems. The most powerful herbivore in European history seemed to offer a solution. 
 
 "We thought we needed a grazer that is fully self-sufficient in case of big predators...and could do the job of grazing big wild areas," says Goderie. "We reasoned that this animal would have to resemble an auroch." 
 
 Rather than attempt the type of gene editing or high-tech de-extinction approaches being employed for species from woolly mammoths to passenger pigeons , Goderie chose a method known as back-breeding to create a substitute bovine he named "Tauros." 
 
 Auroch genes remain present in various breeds of cattle around the continent, and the team identified descendants in Spain, Portugal, Italy and the Balkans. Geneticists advised breeding certain species together to produce offspring closer to the qualities of an auroch, and then breed the offspring. 
 
 Maronesa cow, a close descendent of the auroch. 
 
 The animals get closer with each generation, and the team have the advantage of being able to test the offspring's DNA against the complete genome of an auroch, which was successfully sequenced at University College Dublin. 
 
 "You could see from the first generation that apart from the horn size, there was enough wild in the breed to produce animals far closer to the auroch than we would have expected," says Goderie. 
 
 The ecologist had predicted that seven generations would be necessary for the desired outcome, which might be achieved by 2025. 
 
 The program is now in its fourth generation, and pilot schemes across Europe are offering encouragement. 
 
 'Manolo Uno' - one of the first cross-breeds of the Tauros programme. 
 
 In the wild 
 
 The Tauros programme connected with Rewilding Europe early on, a group that supports the restoration of natural processes through projects that range from rebuilding rivers to introducing apex predators. 
 
 Rewilding Europe was able to provide protected land across the continent; in Croatia, Spain, Portugal, the Czech Republic, and Romania, where Goderie's cross-breeds could test themselves in the wild. In many cases they rose to the challenge. 
 
 "We see progress not only in looks and behavior but also in de-domestication of the animals," he says. "This is a challenging process as they have to adapt to the presence of large packs of wolves." 
 
 Herds of herbivores are habitually decimated by local wolves at the Croatian site, says Goderie. By contrast, the Tauros learned to defend themselves and suffered few losses. 
 
 Selective breeding will continue toward creating the ideal animal. But the current crop is already serving a function. 
 
 Small Tauros herd in the Czech Republic. 
 
 Shades of green 
 
 For Goderie's partners, the auroch project offers an opportunity to restore natural order. 
 
 "We support the come-back of large herbivores as they are key species for the specific role of grazing and browsing," says Frans Schepers, managing director of Rewilding Europe. 
 
 "Bovines can shape habitats and facilitate other species because of their behavior, and the more primitive and close to the wild the better because it means that eventually they can become part of the natural system." 
 
 Many European landscapes are in dire need of grazing animals, which can otherwise become uninhabitable for other species. 
 
 "Without grazing everything becomes forest, or barren land when there is agriculture," says Schepers. "The gradients in between are so important for biodiversity, from open soil to grassland and 'mosaic landscapes.'" 
 
 "The Rhodope Mountains of Bulgaria are among the richest areas for reptiles such as tortoises, snakes and lizards. But they need open spaces or they lose their habitat." 
 
 Aurochs were formidable grazers and are expected to restore dysfunctional ecosystems. 
 
 Targeted intervention 
 
 Critics of rewilding initiatives have suggested that introducing new species could have unintended consequences. 
 
 The International Union for the Conservation of Nature (IUCN) has issued new guidelines in an effort to manage such impacts. 
 
 "Bringing back close approximations of original species may help to reverse losses from emotional to ecological grounds, but often the devil lies in the detail," says Dr. Axel Moehrenschlager, IUCN Chair of the Reintroduction Specialist Group. 
 
 "Typically emphasis is placed on technical feasibility, without sufficient emphasis on risks. Questions abound whether primarily wetland forests like the aurochs used to inhabit still exist, whether it could negatively impact wild or domestic plants or animals, and if it might endanger people." 
 
 The successful introduction of bison in the US shows that such initiatives can have a positive impact, says Dr. Eric Dinerstein of conservation group Resolve, but he adds that one intervention can lead to another. 
 
 "If an ecosystem evolved with large herbivores...there is not an alternative and you need something in its functional role," he says. "But to introduce aurochs, you may need predators as well." ||||| Scientists say they are well on the way to resurrecting an ancient species of super-cow revered by the Nazis after it went extinct nearly 400 years ago. 
 
 The auroch roamed the grassy plains of Europe for 250,000 years until it died out in Poland in 1627, and Adolf Hitler's followers tried to breed a similar beast as part of their Aryan mythology. 
 
 Now conservationists who believe the bovine ancestor was key to preserving the continent's ecosystem have said they are 'rewilding' the fourth generation of their experimental auroch replacement as part of the Tauros Project. 
 
 Founder and ecologist Ronald Goderie told CNN: "We thought we needed a grazer that is fully self-sufficient in case of big predators...and could do the job of grazing big wild areas. We reasoned that this animal would have to resemble an auroch. 
 
 "We see progress not only in looks and behavior but also in de-domestication of the animals." 
 
 In conjunction with the Rewilding Europe group, the Tauros, bred from a number of current species with auroch ancestry, have been released into areas of Spain, Portugal, Croatia, the Czech Republic and Romania, where they have had to contend with wolves and other predators. 
 
 Mr Goderie believes that by 2025, the seventh generation of neo-aurochs will be as close as possible to the originals. 
 
 In 2015 a British farmer was forced to kill off half his herd of auroch-derived Heck cattle because they kept trying to kill him. 
 
 The aggressive breed was produced by German zoologists and brothers Heinz and Lutz Heck, whom the Nazi party commissioned to produce a breed of cattle based on the aurochs, a taller and leaner animal than today's cows. 
 
 Derek Gow said: "What the Germans did with their breeding programme was create something truly primeval. 
 
 "When the Germans were selecting them to create this animal they used Spanish fighting cattle to give them the shape and ferocity they wanted." 
 
 He turned the rogue cows into “very tasty” sausages that tasted a bit like venison, he said. ||||| FRANKLIN GROVE, Ill. — For the first time in almost two centuries, wild bison are roaming east of the Mississippi River. Well, sort of. Even though the beasts have returned to northern Illinois, residents of Chicago should not expect to see them passing through the suburbs anytime soon. The bison were relocated to the Nachusa Grasslands, a conservation program dedicated to restoring Illinois’ native prairie, where they safely roam thousands of fenced-in acres. “The idea of having bison at Nachusa has been around as long as the Nachusa project itself,” said Jeff Walk, the science director for the Nature Conservancy’s Illinois chapter. “They’ve been talking about this for 25 years.” The 30 bison at Nachusa taken to Illinois at the end of last year are part of a regional trend: the rewilding of the Midwest. In recent years, conservation programs in several states in the region have reintroduced large mammals — such as black bears and elk — into areas they once inhabited, before they were hunted to the brink of extinction. In other places, species like wolves and mountain lions have naturally returned to their former habitats. 
 
 ‘The great slaughter’ 
 
 Bison are one of the United States’ most successful conservation stories, but they also exemplify just how much damage was done to the continent during westward expansion. It’s hard to know for sure, but at the beginning of the 1800s, Walk said, there may have been as many as 60 million bison in North America. “And depending on the account, maybe there were 1,000 animals that remained after the great slaughter by the end of the 19th century,” he said. Conservation efforts were largely concentrated in Western and Northern states, in some cases spearheaded by Native American organizations and governments. Today there are approximately 500,000 wild or near-wild bison in the United States. Most modern bison contain varying amounts of cattle DNA after centuries of interbreeding, Walk said. The bison relocated to Nachusa are from a South Dakota herd with some of the least cow DNA found in any bison group. “Most conservation herds have really small amounts of cattle DNA in them,” Walk said. “But we typically do not see very many bison that have obvious domestic cattle traits in terms of their coat color, for example.” While domesticated bison raised for meat production have existed east of the Mississippi River, those now at Nachusa are the first near-wild animals in the region in nearly two centuries. “We needed something to control the grass,” said Cody Considine, Nachusa’s chief ecologist. “Grazing was always the one thing that was missing here.” 
 
 As grazers, bison are one of the last steps of prairie restoration. Although Illinois is called the Prairie State, native prairie makes up less than 1 percent of its land. Ryan Schuessler 
 
 Starting in 1986, the Nature Conservancy, an American environmental conservation organization, began buying land in northern Illinois to restore the state’s native prairie. Since then, the Nachusa Grasslands have grown to nearly 3,500 acres. Although Illinois is nicknamed the Prairie State, native prairie makes up less than one-tenth of 1 percent of the land. “We’ve pretty much destroyed all of it,” Considine said. “You just wish someone could have spared a square mile of prairie, and unfortunately we just don’t have that.” He added, “The state of Illinois prairie is very grim.” But it is not without hope. For outsiders, the bison are interesting news. For those who have been involved in the Nachusa project, they are the last piece of a diverse ecological puzzle. “It’s something very tangible you can see, but it’s definitely not the first animal study or population that we have at Nachusa,” volunteer Michelle Crites said of the bison. “It just happens to be big and fuzzy, and people like bison.” The bison graze on fast-growing species of grasses, allowing other plant species to grow. The population of native dung beetles will increase as a result of the bison’s reintroduction, which will provide more food for the endangered box turtle population. “All of a sudden, when we get a fuzzy animal, when we get a bison, the whole world cares,” said Crites, a 22-year-old Colorado State University student who has volunteered at Nachusa since she was in eighth grade. The extra attention may prove beneficial for Illinois’ prairie conservation efforts. If the work at Nachusa can be replicated elsewhere, there may be hope for the state’s prairie yet. “There still are species that are dependent on this habitat to live,” Considine said. “It’s our heritage, our culture, and we’re preserving and improving and increasing that at Nachusa. Bison just add to that restoration circle, if you will. It’s kind of the last piece of the puzzle of really having a full-functioning prairie.” 
 
 The bison were introduced so they can stamp down and graze on fast-growing grasses that would otherwise choke out other plant life, thus restoring balance to the ecosystem. Ryan Schuessler
– Standing nearly as tall as an elephant, the aurochs grazed for 250,000 years until its extinction in 1627. But its story may not end there: Scientists say they are close to resurrecting the "supercow," once the largest land mammal in Europe, reports CNN. In search of herbivores to maintain land areas at risk of becoming barren, geneticists began breeding aurochs descendants with similar cattle breeds in 2008 and found they could "produce animals far closer to the aurochs than we would have expected," says Ronald Goderie of the Tauros Project. Fourth-generation beasts have now been introduced in Croatia, Spain, Portugal, the Czech Republic, and Romania, with promising results. "We see progress not only in looks and behavior but also in de-domestication of the animals," says Goderie, noting one herd has learned to defend itself against wolves. The hope is that they will become part of the ecosystem to maintain land for other animals. But a rep for the International Union for the Conservation of Nature says it's unclear "whether primarily wetland forests like the aurochs used to inhabit still exist, whether it could negatively impact wild or domestic plants or animals, and if it might endanger people." Indeed, a British farmer had to kill some of his aurochs-descended cattle in 2015 because they tried to kill him, per the Independent. That species, however, came from a Nazi breeding program that used Spanish fighting cattle. (Tinder could save giant pandas from extinction.)