The fatal shooting by zoo officials over the weekend of Harambe, a 17-year-old endangered western lowland gorilla, to save a 3-year-old boy at the Cincinnati Zoo & Botanical Garden has led to a flurry of blame-seeking.

Is the mother of the boy to blame for not noticing that her child climbed a barrier until he tumbled into the gorilla habitat? Is the Ohio zoo the culprit for not having adequate barriers between humans and its primates? Or, as some animal rights advocates argue, does the problem lie with animal captivity itself?

Here’s another possible candidate for blame: the exhibit’s concrete moat. It could have played a role in agitating Harambe enough to violently drag the boy around until he was shot and killed out of fear for the child’s safety.

“A survey of gorilla activity in zoos found that gorillas spent a significantly higher proportion of their time in flat areas than sloped areas and that they also preferred areas with more than one structural element,” said Devin Legisa, researcher at Seattle-based Zoo Design Inc., an architecture and landscaping firm that specializes in moden zoological park exhibits. “Areas like the bottom of moats are uncomfortable to gorillas too because visitors appear larger and more dominant and the sense of refuge is reduced.”

Silverbacks also get antsy when visitors are clustered together in one large looming crowd like the moated exhibit in Cincinnati, Legisa said. Gorillas are less stressed when viewers are visibly broken up into smaller groups, he added, which is a common feature in modern primate exhibit design. 

Older zoo exhibits — Cincinnati’s gorilla exhibit was opened in 1978 from a repurposed greenhouse conservatory — can employ outdated designs of separating humans and dangerous animals, and it can cost millions of dollars to fix the issue.

Lax federal rules and oversight lead to zoos largely deciding on their own the best way to deal with the often-conflicting ideas of visitor accessibility and distance from the animals. In Cincinnati’s case, the only thing keeping human and primate separate was a 3-foot fence and some shrubs, bounded by a 12-foot moat that was accessible to the gorillas. While this was the first incident of its kind at the park, stories of visitors falling or climbing into zoo exhibit pits occur regularly, if also rarely.

Protective concrete moats and pit-like exhibits for primates, bears and big cats are by modern zoological park standards a medieval vestige of an earlier era. For much of the 20th century (and before), larger and more dangerous animals were treated as living displays put there for human enjoyment instead of captive creatures with high levels of awareness and emotions. As zoos began shifting away from spectacle and began to see themselves as educational and scientific institutions, animal exhibits changed with them.

Zoos across the United States have been gradually introducing modern exhibits over the past decades that improve animal welfare while fortifying human-animal barriers. Multimillion-dollar modern primate exhibits can vary, but they all share at least three common features: Animals are given a place for privacy away from the eyes of visitors; they’re given a lot more outdoor space and natural features than in older, more confining exhibits; and visitors are the ones who are “contained” in distinct viewing pavilions behind thick layers of Plexiglas or on high platforms.

But it’s not cheap.

“New, sophisticated exhibits cost millions of dollars, particularly multi-species settings,” said Gigi Allianic, spokeswoman for Seattle’s Woodland Park Zoo, which last year opened a $15 million tiger and bear exhibit. Woodland Park was one of the first in the world to open a “naturalistic gorilla exhibit,” in 1979. Famed primatologists Jane Goodall and the late Dian Fossey served as consultants.

Last year the Houston Zoo opened a $28 million modern gorilla exhibit after 11 years and considerable fundraising efforts. While the zoo features outdoor elevated platforms that could be easily breached, the design relies on people’s sense of self-preservation; if you want to play with the gorillas, there’s no water to break a rather long drop to the ground.

Zoological parks have gone through some profound architectural changes since the middle of the past century. It wasn’t until animal behavior specialists noticed that captive apes, large cats, bears and pachyderms exhibited signs of mental distress in confinement that zoos began taking notice. In the late 1960s U.S. zoos began giving captive primates outdoor space, and paying more attention to addressing the animals’ physiological health, says Zoo Design co-founder Julia Hanuliakova.

“We use to perceive animals as something we needed to completely control in experimental, sterile, hospital-like conditions,” she said. “We’ve known how to take care of their bodies, but now we are trying to figure out how to make them happy.”

The Cincinnati Zoo is more than aware of these needs and has been working for years to address them. Next year it plans to open a $12 million gorilla expansion project that would incorporate modern and year-round viewing for visitors and improved living that offer more primate privacy.

And no concrete moats.