On the Galápagos Islands, wild tomatoes are producing molecules not seen since the Ice Age, reversing a genetic trajectory millions of years in the making. In a study published in Nature Communications, researchers from the University of California, Riverside and the Weizmann Institute of Science have documented a rare and striking example of what they call “reverse evolution.”

“It’s not something we usually expect,” said Adam Jozwiak, a molecular biochemist at UC Riverside and lead author of the study. “But here it is, happening in real time, on a volcanic island.”

The key change is an ancient defense system. Basically, these tomatoes are manufacturing a version of an alkaloid whose molecular fingerprint hasn’t been seen in tomatoes for millions of years. It’s more akin to the compounds found in eggplants, their nightshade relatives.

A Chemical Time Machine

The key to this evolutionary reversal lies in the chemical architecture of alkaloids. They’re bitter, built-in pesticides that protect plants from predators. While most modern tomatoes produce a particular version called 25S, researchers found that wild tomatoes in the western Galápagos are churning out a different form: the 25R version, a molecular relic previously associated with eggplants.

These versions have the same molecular formula and the same connectivity of atoms (atoms are bonded to each other in the same order), but they differ in the way their atoms are arranged in three-dimensional space. This arrangement is called chirality, and although it’s a small change, it has real biological consequences. Two molecules with the same atoms can behave very differently depending on their shape. In humans, this is why one version of a drug might heal, while one with different chirality might be devastating.

Tomatoes on the older, eastern islands of the Galápagos still produce the modern 25S alkaloid. But on the younger, more barren western islands—places like Isabela and Fernandina—the plants have flipped back to the 25R form.

The team believes this isn’t a random accident.

“It could be that the ancestral molecule provides better defense in the harsher western conditions,” said Jozwiak.

The Genetic Gearshift

To understand how this transformation occurred, the researchers zoomed in on an enzyme called GAME8. It’s part of a family of plant enzymes that modify cholesterol into steroidal glycoalkaloids—alkaloids bound to sugar molecules that function as natural pesticides.

GAME8 typically acts like a molecular sculptor, shaping the final form of the alkaloid by controlling the placement of a single hydrogen atom. The difference between modern and ancestral alkaloids comes down to this one stereocenter (called C25) where a subtle enzymatic decision leads to radically different chemistry.

Using gene editing and enzyme assays, the team discovered that mutations in the GAME8 gene in these wild tomatoes had reprogrammed the enzyme. Just a few changes in amino acids—four, to be exact—were enough to make the enzyme generate the ancient 25R alkaloid.

“It’s amazing,” Jozwiak said. “If you change just a few amino acids, you can get a completely different molecule.”

The researchers confirmed their findings by inserting the mutated GAME8 gene into tobacco plants. Sure enough, the plants began producing the same long-lost alkaloids.

Reverse Evolution is a Controversial Concept

Evolution is often described as a one-way street—species adapt and move forward, building on what came before. Sometimes, different evolutionary roads lead to the same place (called convergent evolution). But in rare cases, biology appears to do a U-turn.

Such reversals, sometimes called atavisms, have been observed in laboratory animals, in controlled studies. Chickens have been genetically engineered to grow ancient, tooth-like structures. Stickleback fish in isolated lakes have regrown lost pelvic spines. What makes this tomato story unusual is that it’s not a lab experiment. It’s happening in the wild. And it’s affecting not just individuals, but entire populations.

“Some people don’t believe in this,” said Jozwiak. “But the genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It happened.”

To confirm this wasn’t a one-off mutation, the team analyzed 56 samples from across the islands, focusing on two tomato species: Solanum cheesmaniae and Solanum galapagense. While S. galapagense held steady with the modern alkaloids, populations of S. cheesmaniae on the western islands had clearly flipped to the 25R form.

They even mapped the change geographically. Tomatoes from San Cristóbal, one of the oldest islands, remained chemically modern. But those from the geologically younger Fernandina and Isabela Islands, less than half a million years old, had gone back in time.

Plenty we don’t understand

The study raises tantalizing questions: could such reversals happen in animals? In humans?

Jozwiak isn’t ruling it out.

“Humans, like all organisms, are subject to evolutionary forces,” he told Newsweek. “If environmental conditions shifted dramatically over long timescales, it’s possible that traits from our distant past could re-emerge.”

But he also cautioned that such changes would take “millions of years, if at all.”

There’s no immediate risk to human health from these wild tomatoes, which are not part of the food supply. But understanding how these enzymes work could help scientists engineer crops with safer alkaloid profiles or plants with better pest resistance.

“That knowledge could help us engineer new medicines, design better pest resistance, or even make less toxic produce,” Jozwiak said. “But first, we have to understand how nature does it. This study is one step toward that.”