How Poop Made the World Go 'Round

Extinct? More like ex-stink.

Tens of thousands of years ago, giant land animals roamed the Earth. And these animals—woolly mammoths, giant deer, sloths the size of elephants—would often take breaks from their roaming to deposit vast piles of nutrients on the ground.

In other words, they pooped.

And, considering that some of these massive beasts could consume hundreds of pounds of plants each day, they likely pooped a lot. Everybody does it, to paraphrase the children’s book, but a new paper in the Proceedings of the National Academy of Sciences argues that these animals in particular played a vital role in maintaining the planet’s nutrient cycle, indirectly helping to fertilize places far beyond their reach.

“Marine mammals, seabirds, anadromous fish, and terrestrial animals likely formed an interlinked system recycling nutrients from the ocean depths to the continental interiors,” the authors wrote, “with marine mammals moving nutrients from the deep sea to surface waters, seabirds and anadromous fish moving nutrients from the ocean to land, and large animals moving nutrients away from hotspots into the continental interior.”

Putting the move in bowel movement, in other words, was a complex and multifaceted process, with animals of all kinds doing their, um, duty. (Sorry.)

But over time, extinctions and depleted populations of surviving species have caused this system to deteriorate on pretty much every level. The end of the Ice Age marked mass extinctions of large land animals. More recently, the past few centuries have seen a dramatic drop in whale populations worldwide. And bridging the gap between between land and sea, neither seabirds nor anadromous fish (which live in seawater but return to fresh water to spawn) are as numerous as they once were. Around 27 percent of all seabirds belong to species considered endangered or vulnerable, while anadromous fish populations have fallen to 10 percent of their historical peak.

Welcome to the Anthropoopscene. “We’ve basically done an experiment on the Earth: What happens when you remove these animals?” said Joe Roman, a biologist at the University of Vermont and one of the paper’s co-authors.

What happens is: The world contains less animal poop than it used to, and also fewer ways for the existing poop to spread. Of particular concern is how this has affected the movement of phosphorus, a key component of fertilizer that also happens to be a non-renewable resource. Some scientists estimate that production will begin to decline in the next few decades (although—in a fittingly scatological solution—some have pointed out that reusing phosphorus-rich human urine may help).

“Perhaps one of the reasons we’re running out of phosphorus is because we’ve broken this connection between the oceans and the movements of animals around the planet,” said Roman.

His research has focused on the role of whales, which “dive deep to feed where there’s very little light, no photosynthesis, and they bring those nutrients to the light” when they come up to the surface to expel waste, he said. (For all those wondering: Whale poop, as he described it in a statement, is “a flocculent, liquidy cloud.”) That waste, in turn, feeds algae, which feeds plankton, which feeds fish, which feeds seabirds, and so on up the chain. But the shrunken whale population means that the animals are currently moving only a quarter of the phosphorus they were a few hundred years ago.

Until now, nutrient-cycle research has tended to focus on bacteria over large animals—but the biologists behind the PNAS paper believe that may be because the role of these large animals just hasn’t been visible.

“When oceanography started out, there weren’t really any whales in the ocean. They were very rare,” Roman said. “So of course we didn’t think they were important. We didn’t see them.” Same thing goes for the mastodons and giant sloths: It’s hard to think to measure the impact of something when that something no longer exists. Or: If an animal poops in the woods, and a scientist isn’t around to smell it, did it really happen?

Yes. Yes it did—and it may have nourished the Earth in a way that can’t be fully recreated. But Roman and his colleagues believe that large animals’ role in the nutrient cycle can still be restored to some extent. Preserving and strengthening populations of megafauna like whales and buffalo, they believe, will kickstart the cycle again, increasing the reach of essential substances like phosphorus.

“Think of the Endangered Species Act. Its goal is to remove them from the threat of extinction,” he said. “It’s one important step, but really what we want to do is make these animals ecologically relevant again”—shitting everywhere, before the planet is, well, shit out of luck.