In a surprising twist,wild tomatoes on teh Galápagos Islands are rewriting the rules of evolution. Instead of forging ahead, these plants are reverting to a more primitive genetic state, resurrecting ancient chemical defenses not seen in their kind for millions of years.

These tomatoes, believed to have descended from South American varieties carried to the islands by birds, are now producing a toxic molecular cocktail reminiscent of compounds found in eggplants, rather than the modern tomato.

The University of California,riverside,scientists who authored a recent study in Nature Communications,describe this phenomenon as a possible case of “reverse evolution,” a concept that often sparks debate among evolutionary biologists.

Evolution is typically understood as a one-way journey toward adaptation, not a cyclical return to lost traits. While organisms can sometimes reacquire features similar to those of their ancestors,doing so through the exact same genetic pathways is exceedingly rare.

However, that is precisely what these tomato plants appear to be doing.

“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 to this chemical U-turn lies in alkaloids. Tomatoes, potatoes, eggplants, and other nightshade family members produce these bitter molecules as a natural pesticide, warding off insect predators, fungi, and grazing animals.

While the Galápagos Islands are renowned for their animal life wiht few predators, the same cannot be said for the plant kingdom. This creates a necessity for alkaloid production.

the research team initially embarked on this project due to the potential problems alkaloids can pose in crops. high concentrations can be toxic to humans,making it crucial to understand and control their production in edible fruits and tubers.

“Our group has been working hard to characterize the steps involved in alkaloid synthesis, so that we can try and control it,” Jozwiak said.

The unique aspect of these Galápagos tomatoes is not simply their alkaloid production, but the fact that they are producing versions that have not been present in tomatoes since their earliest evolutionary stages.

The research team analyzed over 30 tomato samples collected from various geographic locations across the islands. They discovered that plants on the eastern islands produced the same alkaloids found in modern cultivated tomatoes. However, tomatoes on the younger, western islands were producing a different version, bearing the molecular fingerprint of eggplant relatives from millions of years ago.

This difference boils down to stereochemistry, or the arrangement of atoms in three-dimensional space. Two molecules can contain the same atoms but behave differently based on their arrangement.

To understand how the tomatoes made this switch, the researchers examined the enzymes responsible for assembling these alkaloid molecules. They found that changing just four amino acids in a single enzyme was enough to alter the molecule’s structure from modern to ancestral.

They confirmed this by synthesizing the genes coding for these enzymes in the lab and inserting them into tobacco plants, which then began producing the old compounds.

The pattern was not random, but aligned with geography.tomatoes on the eastern, older islands, which are more stable and biologically diverse, produced modern alkaloids. Those on the younger, western islands, with more barren landscapes and less developed soil, had reverted to the older chemistry.

The researchers believe that the environment on the newer islands may be driving this reversal. “It could be that the ancestral molecule provides better defense in the harsher western conditions,” Jozwiak said.

to confirm the direction of this change, the team used evolutionary modeling to infer the traits of long-extinct ancestors based on modern DNA. The tomatoes on the younger islands matched the likely alkaloid production of those early ancestors.

While calling this “reverse evolution” is a bold claim, the reappearance of old traits has been documented in other species, including snakes, fish, and even bacteria. However,it is rarely this clear or chemically precise.

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

This type of change may not be limited to plants.”I think it could happen to humans,” Jozwiak said. “It wouldn’t happen in a year or two, but over time, maybe, if environmental conditions change enough.”

While Jozwiak’s research doesn’t focus on humans, he emphasizes the serious implications of evolution being more flexible than previously thought. Traits long lost can resurface, and ancient genes can reawaken. This study suggests that life can sometimes progress by reaching into the past.

“If you change just a few amino acids, you can get a fully different molecule,” Jozwiak said.”That knowledge could help us engineer new medicines, design better pest resistance, or even make less toxic produce. But first, we have to understand how nature does it. This study is one step toward that.”