"Before you do anything else,” curator Chris Meyer said the minute I arrived at the National Museum of Natural History's Invertebrate Zoology collection, “you have to vote for beauty.”

He led me through a maze of cabinets to a counter laid out with a wire bingo cage and dozens of cowrie shells. Meyer instructed me to spin the cage five times and read out the numbers that appeared, then handed me a box containing the five corresponding shells.

Nestled in their box, the cowries reminded me of a child's marble collection. Each oblong shell had the same basic shape: a rounded, impossibly smooth top and a flat bottom with a slit-like opening in the center. The smallest was no bigger than my thumbnail, with green and brown speckles dotting its slick surface. The largest was as big as my palm. It had a lovely orange hue, and I flipped it over to reveal an opening edged with fine purple teeth.

I was supposed to rank the shells from most beautiful to least. Later, Meyer would add my ranking to a database that he is using to pinpoint trends in visitors' conception of beauty. You can rank them yourself here.

I found it difficult to choose a favorite.

“They are spectacular,” Meyer agreed, “They're like nature's gems.”

Drawn by their exquisite appearance, humans have been collecting cowries for tens of thousands of years. They may well be the original collected objects — the prehistoric predecessors to diamonds and gold. The oldest examples of jewelry ever found, dating back as early as 100,000 years, were made of cowries and other shells. As time went on, cowries became symbols of power and a form of currency. European explorers filled their curio cabinets with the creatures. Today, collectors search the tropics in search of ever-rarer and more perfect specimens.

“For whatever reason, people are just fascinated,” Meyer said. “And that's what we're trying to understand. What is it that is attracting people to have this fascination? What do people value about them?”

A cowrie, or any natural object, can be valued in a number of ways. There's the obvious metric, price, which for cowries is inextricably tied to their beauty. The most magnificent cowries are “like works of art” Meyer said. It's rumored that the most expensive cowrie ever sold for more than $50,000. The NMNH collection, which contains some 50,000 specimens, is likely worth millions (though the Smithsonian would tell you that its collections are “invaluable.") 

Then there's cowries' scientific value. The Cypraeidae family includes more than 200 living species of cowrie and extends back to the age of the dinosaurs. The animals themselves are sea snails: small and slimy, with flaps of flesh that extend out over the shell to enclose it like a jacket. These flaps of skin secrete the pigments that create the characteristic complex designs on the shell's surface.

Cowries hide in caves and under rocks during the day and come alive at night, when they feed on corals and algae and are fed on by crabs and octopuses. The animals can be used as bellwethers of coral reef diversity, and their shells make extraordinarily good fossils, so they can be studied to understand ancient reefs.

“They're really useful as a model,” said Meyer, whose research is focused on why cowries diversify into new species and what makes them go extinct.

But there's a third approach to valuing nature — one that has nothing to do with how much a person might pay for it, or what a scientist might learn.

“What is the value of the animal in its habitat?” Meyer asked. “Species perform very particular roles in ecosystems, and the potential impacts of removing them from these ecosystems are hard to predict.”

“So, what if tomorrow we wake up and there are no cowries on the reefs? What would happen?”

The question has loomed large in Meyer's mind recently. A few years ago, Meyer received word that a collector working off the coast of Oman had just uncovered a species long believed to be extinct: Cypraea teulerei. 

This species isn't necessarily the loveliest member of its group — the strawberry-sized shells are dappled brown and gray with a chocolate-colored blotch on top and a bold white stripe down the middle — but it is exceedingly rare. The teulerei is a “living fossil,” a member of an ancient lineage with no other surviving species, and it was previously thought to live only in certain areas around the island of Masirah off Oman. Dwelling in the shallow, crystalline waters of the Arabian Sea, it was once easy to collect; enthusiasts scooped the shells up by the bucketful and sold them for as much as $500. Within decades, the area where they were known to live had been picked clean.

Sea creatures like cowries are generally resilient to extinction, Meyer said. They reproduce by the hundreds, usually by spraying eggs into the water column and letting them float across the sea. This wide distribution makes it difficult to eliminate any one species by hand — though the global impacts of pollution and climate change mean humans can still pose a threat.

But the teulerei is a “direct developer.” It broods its eggs in discarded clam shells; once hatched, the young only ever travel as far as they can crawl. As a consequence, the species is concentrated in small, highly specialized areas. And once those areas has been identified by collectors, the cowries are in danger.

No one had collected a live teulerei in at least 20 years when, in 2012, an Italian enthusiast named Massimo Scali announced he'd found a new cache of teulereis off the relatively unexplored southern coast of Masirah.

Now Meyer has been invited to go to Oman to collect the rare creatures for his research at the museum.

“I'm relatively conflicted about it,” Meyer told me over the phone several weeks ago. “If you’re going to take the life of a creature and put it in a collection … there are real ethical questions involved.”

The teulerei is rare, ancient, and arguably on the brink of extinction, he noted — all points against a collecting trip. Then again, the sole surviving member of a 25-million-year-old lineage could contain untold secrets about cowries' evolutionary past. Plus, he mused, death is the fate of all animals. A cowrie that doesn't get collected will just end up in a fish gut.

Even so, “knowing what we know about it, I would emphasize probably not collecting more,” he said. 

By the time I visited Meyer in the invertebrate zoology collection a week later, his thinking was more settled. If he gets permission from the Omani government, he will travel to Masirah to collect — and he'll use the opportunity to raise awareness of the cowries' vulnerability.

“The situation with teulerei … forces me to confront the impacts we have on our planet and to take an active role in how we address conservation and mitigate the human footprint on the planet,” he said. “And it hits home for me, as a researcher on cowries, tremendously. It was like, wow … it's going to be hard to get out of bed tomorrow unless I do something. Because there aren't very many people out there who would.”

Ultimately, Meyer decided that someone would need to stand up for cowries' innate value — the kind that can't be measured in dollars or number of published studies.

He will try to keep the impact of his field research to a minimum, limiting his sampling to small amounts of tissue for genetic analysis. He will also recommend that researchers etch the shells they find with a small knife, marring the intricate patterns of their shells. This doesn't hurt the animal at all — cowries have weak eyes, hunt at night, and probably “care a heck of a lot more how someone smells” than what their shell looks like, Meyer said. Yet the etching spoils cowries' value on the collectors' market.

Some might consider this act of defacement equal to scratching a Michaelangelo sculpture or the face of a precious gem. But Meyer thinks his colleagues will understand why it's necessary. Without more cautious collecting, there will be no teulerei left for anyone in a matter of years.

“We're in this interesting crux of documenting and inventorying the diversity of the planet in a way that no generation before us could, right as that diversity is disappearing,” he said. “I just think that part of the moral imperative of being a good scientist, is telling these stories and documenting change and having good example species that people care about.”

Which brings him back to the “vote for beauty” project. The study's stated goal is to understand what draws people to natural objects, so that the museum can do a better job picking its “poster child” for exhibits on biodiversity. In this way, the various metrics for calculating a cowrie's value can complement each other: their beauty might help scientists protect the animals and their habitats and ensure the future of cowrie research.

On weekday afternoons, Meyer and his colleagues will bring a box of cowries and the bingo cage up into the ocean exhibit hall. The experiment always draws a crowd. So far, the scientists have catalogued the preferences of more than 10,000 visitors to the museum. They've found that children under 10 prefer bigger shells, while women like small ones. Everyone gravitates toward shells with bright colors and bold patterns — contrast is what makes humans click. By now, Meyer can usually predict how a person will rank their shells as soon as he hands them over.

But not always.

“What's fascinating is everybody has their own way of looking at the world, and it's different yet similar. There’s things you can predict and there’s things that will surprise you,” he said. “That’s the beauty of diversity.”

Tales From the Vault: Science museums are home to vast research collections, most of which the public never gets to see — until now. Once a month, Speaking of Science will go behind the scenes at our favorite museums to introduce readers to the fascinating objects and people we find there. Read past installments here.

Correction: An earlier version of this post misspelled the species name of the threatened cowrie Cypraea teulerei.