Last week, the issue of what to do with wild horses stampeded back into the news cycle. An advisory board to the Bureau of Land Management (BLM) proposed a mass culling of tens of thousands of wild horses and donkeys currently kept in captivity to cut costs and free up public land for livestock grazing, Niraj Chokshi reports for the New York Times. Animal rights activists called foul, descrying the recommendation inhumane—an outcry that prompted the agency to reassure the public that they did not plan to follow the advice.

But this is not the first and definitely not the last time this debate will be had about the horses. Though it seems at odds with this iconic symbol the American West, the controversy over the horses comes from these creatures long history on the continent.

Wild or domesticated, the immediate ancestors of all horses in the western hemisphere can trace their ancestry back to the creatures European explorers and colonists brought with them in the 15th and 16th centuries. From there they were traded with Native Americans, released or escaped into the wild to breed and form their own feral herds, Coburn Dukeheart reports for National Geographic. But while these were the earliest horses to roam the plains in relatively recent history, research suggests they weren’t the first.

For millions of years, wild horses roamed what is now the American West alongside charismatic creatures, such as wooly mammoths and giant sloths. Then, somewhere around 10,000 years ago, some crossed the Bering land bridge into Asia, where they thrived and spread, Dukeheart reports. Meanwhile, their fellows back in the Americas went extinct. Thousands of years later, the explorers brought the distant relatives of these early wild horses back to the prairies once again.

This is where modern problems with the creatures come in. Though some people consider the horses natives because their ancient heritage, they are still technically an introduced species. Since the prairies and plains of the west are perfect habitats for these herds and they have few predators, they breed and spread quickly, often competing with nearby farmers and ranchers for natural resources. Once treasured as a symbol of the West, they now are commonly treated as pests—many that wander onto private property are captured or killed, Dukeheart reports.

In the 1970s, however, federal lawmakers passed a bill protecting the wild horse herds. Since then, the BLM has managed the wild populations, but animal rights activists have called the agency’s methods into question. Currently, the BLM relies on sterilization and capture to try to keep wild horse population numbers under control, Alex Swerdloff writes for Munchies. But sterilization remains controversial and capture isn't a complete solution. What do they do with the captured horses? Adoption of these creatures is tough, they require an enormous amount of time to train and raise, and few people are willing to put in the effort. The other option is euthanasia, which brings the opposing groups to blows upon every mention.

But something must be done about the horses. The BLM stock has swelled over the years to over 45,000 horses—and with the cost of caring for them hovering around about $50 million a year, keeping them penned up indefinitely is an expensive proposition, Swerdloff reports.

How to best manage the wild horses of the American West is a tough question, and right now there are no options that please all sides. Though these creatures symbolize the freedom and spirit of the Wild West, no one has yet figured out how to peacefully coexist.