Recent studies have unveiled a fascinating phenomenon occurring among the wild tomato plants on the Galápagos Islands, specifically the younger, volcanic islands. These plants are exhibiting a remarkable behavior by seemingly discarding millions of years of evolutionary advancements, reverting back to a more ancestral genetic form. This unusual change includes the reactivation of long-dormant chemical defenses, leading to the production of a toxic blend of molecules not seen in these tomatoes for millions of years.
The wild tomatoes, which are believed to have descended from South American species dispersed by birds, have started synthesizing a chemical mixture that bears more resemblance to compounds found in eggplants than in today’s cultivated tomatoes. This remarkable discovery was detailed in a recent study published in Nature Communications by researchers from the University of California, Riverside. This phenomenon has been described as a potential instance of "reverse evolution"—a concept that often sparks debate among evolutionary scientists.
The notion of reverse evolution challenges the traditional perspective that evolution exclusively progresses toward increasingly adapted forms. While traits reminiscent of distant ancestors occasionally resurface, it is extraordinarily rare for them to do so through the same genetic mechanisms. However, the findings suggest that this is precisely what is happening in these wild tomatoes. “It’s not something we usually expect,” stated Adam Jozwiak, a molecular biochemist at UC Riverside and the lead author of the study. “But here it is, happening in real time, on a volcanic island.”
At the core of this chemical transformation are alkaloids, which play a crucial role in plant defense. These bitter-tasting molecules, found in tomatoes, potatoes, eggplants, and other members of the nightshade family, act as natural pesticides against insects, fungi, and herbivores. Despite the Galápagos Islands being known for their scant animal predators, plants still require these chemical defenses for survival. The research team initiated this study because while alkaloids are beneficial for plants, they can pose health risks to humans in high concentrations. “Our group has been working hard to characterize the steps involved in alkaloid synthesis, so that we can try and control it,” Jozwiak explained.
What makes the Galápagos tomatoes particularly noteworthy is not only their production of alkaloids but also the fact that they are generating types not previously observed in modern tomatoes. The research team examined over 30 tomato specimens from different locations across the islands. They found that tomatoes on the eastern islands produced alkaloids akin to those found in contemporary cultivated varieties, while those on the younger western islands were synthesizing a different form that matched the chemical profile of ancient eggplant relatives.
This distinction in alkaloid production is attributed to stereochemistry, which involves the spatial arrangement of atoms within a molecule. This means that two compounds can consist of the same atoms yet exhibit completely different functions based on the positioning of those atoms. The research revealed that just a few mutations were responsible for this significant shift in alkaloid structure. Specifically, altering four amino acids in a single enzyme was sufficient to change the molecule’s configuration from modern to ancestral.
The pattern observed was not random; it correlated with geography. Tomatoes on the eastern, older islands, which are biologically diverse and more stable, produced modern alkaloids. In contrast, those on the younger, western islands, characterized by harsher conditions and less developed soil, adopted the older chemical profile. The researchers speculate that the environmental conditions on these newer islands may be driving this reversal. “It could be that the ancestral molecule provides better defense in the harsher western conditions,” Jozwiak noted.
To confirm the direction of this change, the research team conducted a form of evolutionary modeling that utilizes modern DNA to infer the traits of long-extinct ancestors. The tomatoes from the younger islands displayed characteristics that likely resemble those of early ancestors. However, labeling this phenomenon as “reverse evolution” is a bold statement. While the reappearance of ancient traits has been documented in various species, including snakes and fish, it is rarely as clear-cut or chemically precise as observed in these tomatoes.
“Some people don’t believe in this,” Jozwiak stated. “But the genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It happened.” This kind of evolutionary change may not be confined to plants alone. If such reversals can occur in tomatoes, similar processes could theoretically happen in other species, including humans. “I think it could happen to humans,” Jozwiak added. “It wouldn’t happen in a year or two, but over time, maybe, if environmental conditions change enough.”
Although Jozwiak's research does not focus on humans, the implications of the flexibility of evolution are significant. Traits that have long been lost can resurface, and ancient genes can be reactivated. As this study suggests, life can sometimes forge ahead by reaching back into its evolutionary past. “If you change just a few amino acids, you can get a completely different molecule,” Jozwiak remarked. “That knowledge could help us engineer new medicines, design better pest resistance, or even produce less toxic crops. But first, we need to understand how nature accomplishes this. This study is a significant step in that direction.”
Reference: “Enzymatic twists evolved stereo-divergent alkaloids in the Solanaceae family” by Adam Jozwiak, Michaela Almaria, Jianghua Cai, Sayantan Panda, Hadas Price, Ron Vunsh, Margarita Pliner, Sagit Meir, Ilana Rogachev, and Asaph Aharoni, 18 June 2025, Nature Communications. DOI: 10.1038/s41467-025-59290-4.
