Debate continues as to the origins of the COVID-19 pandemic, propelled in part by U.S. Department of Energy and the Federal Bureau of Investigation, which conducted their own investigations. Both issued tentative conclusions that the disease originated in a scientific facility, fueling the lab leak theory. But scientists point to a likely animal source, ranging from horseshoe bats to raccoon dogs to even outer space.

We’ve been here before with new diseases, according to epidemiologist and disease ecologist Jonna Mazet. Each year, scientists identify an average of five new diseases that have jumped from animals to humans. Past examples include Ebola, from fruit bats; Hepatitis E, from pigs; West Nile Virus, from birds; and Yellow Fever, from African primates. Scientists estimate that some 500,000 other viruses could one day infect human cells.

Read More: Zoonotic Diseases That Have Been Transferred to Humans

“It’s not the animals that are putting people at risk,” says Mazet in the video. “It’s our human behavior and the risky things we do that put ourselves at risk for these viruses. They don’t jump out and grab us.”

More than ever, humans are increasingly encroaching on wild lands, due to population growth, and humans and wildlife are living and dying in close contact. But whether such a relationship led to the COVID-19 pandemic is still unknown.

“There will be a lot of information that comes out over decades,” says Mazet in the video, “and we’ll be able to piece some things together to understand what really happened.”

This video originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews. You can view the original here.