Over the Memorial Day weekend, a 4-year-old boy climbed the guardrail at the Cincinnati Zoo and into the enclosure of a 17-year-old silverback gorilla named Harambe. By now, most people know how this played out. The boy’s mother had lost track of him, long enough that he crawled over a wall and fell 10 feet into a moat at the bottom. Harambe stood over the child, as if protecting him from the people yelling above, then grabbed the boy’s arm and jerked him through the water. Tranquilizing the gorilla wasn’t an option, the zoo director would later say, because the sedative takes time. And no one could predict how a drugged animal that weighs 450 pounds would react. So they shot Harambe dead.

Zoos have changed a lot in the past 50 years. The openness of Harambe’s enclosure, the cliffs separated by a moat, were designed to lend it a more natural feel for viewers, and to simulate wild environment for the gorillas. It is a departure from the bars and sanitized tile floors of past zoo design. As people become more sensitive to the lives of these animals, they’ve understood how flat concrete and tight confinement can cause depression, even phobia, in everything from donkeys to snow leopards.

Someone at the Cincinnati Zoo caught much of what happened on video (not the shooting), and immediately afterward people blamed both the mother—why wasn’t she watching her son?—and the zoo director—was there no other option?

Few people have asked why a zoo, full of dangerous, or not-so dangerous animals, is even necessary. That might be because calling for an end to zoos has typically been the cause of poets and animal-rights activists. Most past arguments against zoos have focused on the insensitivity toward animals. As Benjamin Wallace-Wells wrote two years ago in a piece for New York magazine titled, “The Case for the End of the Modern Zoo”:

I realize that to even raise this issue makes you sound like some kind of sour, rule-bound vegetarian, so let me make clear my position up front: I love zoos. My daughter is not quite 2, and the zoo brings out all of her best and least complicated emotions — awe, delight, empathy.

But concern for caged animals has caught enough mainstream interest that New York and California introduced bills that would outlaw killer whales kept in captivity. Their focus on killer whales is in large part owed to a 2013 documentary called Blackfish, but it proves that it has become a concern for more than a fringe of animal-rights advocates. So much so, that last March, SeaWorld Parks & Entertainment said it would stop breeding captive killer whales. And if keeping an orca in large tank is unethical, then why not an elephant, a tiger, or a 17-year-old western lowland gorilla?

The argument for zoos is often that they serve to educate the public, they give people who can’t afford to travel a chance to see the animals, and that zoos serve as important conservation centers.  There is a distinction, of course, between good zoos and bad zoos. In the 1980s, a study of animals at the San Diego Zoo found some had died from frequent tranquilizing, malnutrition, and that some had suffered repeated injuries while being transported. Since that report, and with a rise in scientists who study animal behavior, zoos have tried to improve conditions for their caged animals. This was partly the cause for more natural-looking enclosures––like the gorilla exhibit in Cincinnati––because “empty, boring, barren enclosures” can cause depression or aggression in some animals, including primates, according to a study by Plymouth University, in England.

In that regard, the Cincinnati Zoo is by all means a good zoo, providing Harambe a relatively comfortable enclosure. It’s not simple to accommodate the world’s largest primate. Gorillas are as strong as eight men, they can be aggressive, and they’re also endangered. For all those reason, they’re fascinating to watch. And unless someone planned to visit the forests of Central Africa, a zoo is the only place a person will likely see one—or for that matter a wolf, a rhino, or a rhinoceros hornbill (a bird kept at the Cincinnati Zoo). Of course, there’s TV, “but that really does pale next to seeing a living creature in the flesh, hearing it, smelling it, watching what it does and having the time to absorb details,” wrote David Hone, a paleontologist and writer who has defended zoos.

So zoos teach. Or do they?

In 2014, Eric Jensen, a sociologist at the University of Warwick, published a study in the journal Conservation Biology that surveyed 3,000 children before and after a zoo visit and found only one-third had a “positive” learning experience, meaning they’d learned something factual. About 15 percent of the kids picked up incorrect information. But perhaps what pro-zoo people mean, and more in line with what Hone argued in his article, was that zoos are a type of consciousness expander. They expose people young and old to something they’d never otherwise be able to see. For example, a child’s parents may take her to the Cincinnati Zoo and years afterward she might remember that moment and dream of a job working alongside animals—and achieve that goal.

Obviously, children are not the only group to learn from zoos. Researchers visit them, observe and study the animals, and help animal conservation. In this case, zoos act like temples of sanctuary, where human intervention inside protects a species from human threats outside. This happened with the California condor, of which there were only 23 left in 1982. By 1987 researchers and conservationists had captured every last one and moved them into a captive-breeding program. Today, thanks in part to the Los Angeles Zoo, there are hundreds of condors living in captivity, and about 75 have been released back into the wild.

It is true zoos have played a massive role in conserving, and in the recovery of, some species, but this is a relatively small portion of the animals zoos work with. As Tim Zimmerman pointed out in an article for Outside magazine last year, the Association of Zoos & Aquariums reported that of all the animals at the 228 zoos it accredits, only 30 species are being worked with for recovery. And of those 30 cases, most can’t be re-introduced into the wild. So the species will exist, but never as they once did.

Humans have always caught and caged animals, either for entertainment, or as an assertion of power. The Sumerians in ancient Mesopotamia did it more than 4,000 years ago. Later, Alexander the Great was said to take special care of his menagerie of bears and monkeys. The Aztecs in the Americas, the early Chinese––both caged animals. The first modern zoos emerged in the 19th century, but have changed drastically since, slowly becoming more hospitable toward animals as people’s empathy toward them grows.

Now, in Denmark, the human/animal role of zoos is already being reversed. At Zootopia, BIG, the architecture firm, designed a 300-acre zoo without bars, fences or glass, which it said makes for the “best possible and freest possible environment for the animals.” The first phase is scheduled to open in 2019. It’s not a preserve––as those who want zoos shut down have called for––but it is an advancement in how people think of holding captive animals. Zootopia’s layout would let animals roam land that encircles a doughnut-hole observation center. And though people can walk through tunnels and poke their heads up for a closer look, in this design it’s not dangerous animals like the silverback gorilla that are caged, it’s the humans.