This plant no longer exists. But you can still smell it. - National Geographic

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Telephones were a new invention, the Model T Ford was selling briskly, and William Howard Taft was U.S. president the last time anyone might have smelled a Hibiscadelphus wilderianus tree blooming in the wild. A distant cousin of Hawaii’s famous hibiscus flowers, the tree was native to the southern slope of Mount Haleakala, on the island of Maui. It’s likely that H. wilderianus went extinct between 1910 and 1913, judging from reported sightings of it dying along with other tree species that ranchers had slashed to clear space for cattle.

More than a century later, a group of scientists would wonder whether extinction was truly the end of the species’ story. What if this plant no longer seen in the wild—found only between dry pages in an archive—could be brought back to life, at least partially?

“We were sitting around and thinking, What if we could do Jurassic Park?” says Christina Agapakis, the creative director at Ginkgo Bioworks, a Boston-based biotech company. “It was this sort of dreamy conversation, and we thought maybe we could.”

Just a small sample of the Harvard herbarium specimen of Hibiscadelphus wilderianus was needed to identify the extinct plant’s scent molecules.

GRACE CHUANG AT HARVARD UNIVERSITY HERBARIA

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Within five years, they had opened an aromatic window to the past. Using DNA reconstruction and synthetic biology, they resurrected the tart juniper scent of the vanished Hawaiian tree’s bloom.

Resurrecting a smell isn’t just about smelling something that no longer exists, says Sissel Tolaas, a researcher and artist whose Smell Research Lab in Berlin worked with Ginkgo on the plant project. “Through smell you engage with memory and emotion,” she says. Calling forth a long-lost smell is a way of experiencing the extinct feelings it might have sparked, a whiff of the past.

Today an estimated 40 percent of Earth’s plants are in danger of going extinct, according to a 2020 report by the Royal Botanic Gardens, Kew. Many more will disappear before scientists even realize they exist.

Bringing back what was lost wasn’t easy. Agapakis and her team first had to find enough of their targets’ remains. Scientists in the fictional Jurassic Park tapped a mosquito preserved in amber; Agapakis first hypothesized permafrost might contain preserved remnants of extinct plants. When that proved a dead end, she tried the Harvard University Herbaria & Libraries, a 20-minute drive from Ginkgo’s headquarters. In Harvard’s collection of dried plant specimens pressed between the large beige pages of books, 20 extinct plants were logged. The herbarium allowed Agapakis to take samples from 14; three were chosen for resurrection. Hibiscadelphus wilderianus was one.

The second, Orbexilum stipulatum, last seen on a Kentucky river island, was presumed extinct in 1881. The third was labeled as Leucadendron grandiflorum, native to South Africa and last seen in 1806. A sample the size of a pinkie fingernail was taken from each of the three plants and sent to the University of California, Santa Cruz Paleogenomics Lab, where geneticists sequenced the plants’ DNA.

Orbexilum stipulatum: The small flowering plant, commonly known as Falls-of-the-Ohio scurfpea, was presumed extinct in 1881. Like the Hibiscadelphus tree in Maui, the scurfpea was wiped out by development: A river dam project flooded its last known habitat in Kentucky. Its flower’s re-created scent smelled “citrusy and candy-like” to project artist Alexandra Daisy Ginsberg.

Photograph by The Gray Herbarium of Harvard University

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Leucadendron grandiflorum: Commonly known as the Wynberg conebush, the small white-flowered plant is native to South Africa. After its habitat was taken for vineyards, it was last seen in 1806. Research for Ginkgo’s project revealed two different specimens labeled as Wynberg conebush, throwing into doubt the plant’s identification. What Tolaas reconstructed smelled “deep and tobacco-y” to Ginsberg. Meanwhile, South African conservationists hope to bring back the indigenous plant: By safely burning part of the land that once was conebush habitat, they may unlock dormant seeds in the soil.

Photograph by The Herbarium of the Arnold Arboretum of Harvard University

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When an organism dies, sunlight, water, and microbes immediately begin to degrade the DNA in its cells—so to reconstruct it, scientists must piece together the fragments of DNA that remain. Molecular biologist Beth Shapiro, who oversees the paleogenomics lab, likens the process to “a trillion-piece puzzle.”

The author of How to Clone a Mammoth, Shapiro is a pioneer in analyzing and reconstructing ancient DNA. She and her team used an expansive digital database of known DNA to identify the genetic fragments from the extinct plant samples, and then pieced together the genes of plant enzymes responsible for making scent molecules.

With the help of synthetic biology company Twist Bioscience, the digital reconstructions were printed as synthetic DNA sequences. Back at Ginkgo, these sequences encoding the smell-producing enzymes were inserted in yeast, which grew and produced scent molecules. Yeast is a powerhouse in the field of synthetic biology, Agapakis says, used to make everything from medicine to food flavoring.

Ginkgo then sent the list of molecules to Tolaas’s Berlin lab, where the artistic part of this art-and-science project began.

Tolaas reconstructs smells from molecules the way a writer uses letters to construct words. She references her smell library, a collection 25 years in the making that includes 10,000 molecules and compositions, organized in small jars and a database. Referencing the molecules sent from Ginkgo, she figured out what scent they might produce by matching their molecular structure to the structure of the smells in her library and in other collections. Over eight months, she tinkered with the formula—highlighting or de-emphasizing certain notes—to create her unique interpretation of how the plants might have smelled.

“I am not adding anything that is not there,” Tolaas says. “I’m playing with the facts.”

She sent back 10 different variations of the Hawaiian plant’s smell and six variations for the Kentucky and South African plants. Each version was a slightly different arrangement of the scent molecules in the three plants and produced a range of smells they may have emitted in the wild.

When Agapakis smelled the extinct scents for the first time, she was moved. “We’re smelling something that’s lost forever. That hits you emotionally,” she says. “You don’t want to think about extinction most of the time and how grim that is. Imagine the diversity we’re losing every day. Imagine all that magic that’s there.”

The synthetic biology used to revive extinct scents is the next frontier in innovation, Agapakis says. So far, Ginkgo Bioworks has had a hand in creating microbes that replace chemical fertilizers, concocting skin-care products with living bacteria, and cultivating proteins used in meat alternatives. Agapakis foresees integrating synthetic biology into daily life the way electronics and wireless internet are now everyday tools.

In that future, she wonders aloud, “What if we could have a ‘living’ everything?”

Sarah Gibbens is a staff writer covering the environment.

This story appears in the December 2021 issue of National Geographic magazine.

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