He spent an hour pulling data together before cueing up the program. He clicked enter, and goosebumps popped up on his arms as saw the number on the screen: 5,000.

One test could easily be a fluke. So Mora tried birds next. Scientists have a reasonable estimate of the number of bird species on the planet—9,988. Mora once again set up the program and pressed enter. This time, he closed his eyes.

“There was so much anticipation that I didn’t want to see the number,” he told me.

“I have never won the lottery,” Mora said, “but I’m sure that probably felt pretty close to winning a million dollars.”

“I need to show you something important,” Mora told Worm. When he saw Mora’s computer screen, the hair on the back of his neck stood up.

“I remember looking at each other and being in awe,” Worm told me later. “It was immediately clear that this was a major advance.”

They immediately started cranking out a paper, Mora said. They were already about 80 percent done by noon. Since they knew they could figure out the correct number of mammals and birds just from plugging in genuses, orders and other taxonomic groups, they could now estimate things like fish and bacteria using the same methods. Just as their method could estimate mammals without data about all the existing mammal species, it could estimate the number of fish that were still undiscovered. Within a month, the scientists knew how many species there were in the sea.

But they didn’t stop there. They used the method to estimate the number of animal, plant, bacteria and all the other species on the planet.

Their conclusion: there are 8. 7 million species on Earth, and humans have yet to discover about 86 percent of them.

As he stared at a graph that summed up their findings on a recent morning, Mora got goosebumps again.

“It was one of the highlights of my life,” he said. “I wish I could share the feeling with everybody.”

The paper made headlines around the world when they published it in PLOS Biology in 2011. There were thousands of news articles on it, including in The New York Times, National Geographic and The Washington Post. A thread on Reddit, “How do we know that we only know about 14% of our species?” was upvoted nearly 14,000 times. El Espectador, a Colombian newspaper, even named Mora one of its “people of the year,” along with the Colombian president.

But at least one person missed out on all the hype: Carlo Ricotta. Even seven years later, Mora still has no idea who Ricotta is. He’s never talked to him. He hasn’t come across more published work from the Italian ecologist. I couldn’t find anything Ricotta had ever said about Mora’s study, either. Was he proud his paper had gone so far? Disappointed he’d been left out of the excitement?

I emailed Ricotta. “I’m writing an article about how many species there are on Earth, and I noticed you’ve studied that question,” I wrote.

“Unfortunately, I have never studied that question,” he wrote back a few hours later. “So, I will probably be of very little help for your article.”

I spent an inordinate amount of time trying to explain everything to him over email, pointing out that he wrote a paper on the subject over a decade ago that spawned a finding about species all over the planet. He eventually agreed to talk with me on Skype.

“I have nothing against telling you what we did,” he wrote. “But this is probably very different from what you expect.”

When we finally talked, he was friendly but confused. He explained that his paper just looked at seeds on a mountain range, not all the species on Earth. When I told him scientists had used his method to calculate the number of species on the planet, he told me that he doubted it would work. We ended the conversation quickly, and I sent him Mora’s paper, as well as some news articles about it.

The next day, he sent me an email consisting of only five words “Hi. I did my homework.”

We talked again a few days later, finally on the same page. He told me he liked Mora’s paper well enough.

“I think it makes sense,” he said. “It’s a very elegant approach.”

But he still didn’t seem particularly excited about either the study or his own contribution to it. It had happened so long ago and was such a small part of his life that he barely remembered it. The paper had started as an undergraduate student’s thesis. He and another professor had simply worked with the student to use existing data to come up with a mathematical formula.

Unlike Mora’s endeavor, there weren’t thousands of scientists or billions of dollars involved. Just some basic math.

“You can have fun even with low-cost science,” he mused. “I’m happy it was used to build something.”

Others in the scientific world were more effusive in their praise of Mora, Worm, and their coauthors’ paper. “It is a remarkable testament to humanity’s narcissism that we know the number of books in the US Library of Congress on 1 February, 2011 was 22,194,656, but cannot tell you—to within an order-of-magnitude—how many distinct species of plants and animals we share our world with,” wrote Robert May, a zoology professor at Oxford University who had been trying to calculate this number since the 1990s.