In a fascinating case of potential reverse evolution, wild tomatoes in the Galapagos Islands have reactivated an ancient defense mechanism that has not been observed in millions of years. The species, scientifically known as Solanum pennellii, was first studied in 2024 while researchers were examining alkaloids—natural compounds that serve as built-in pesticides for plants.
Located hundreds of miles off the coast of Ecuador, the Galapagos Islands were crucial in shaping Charles Darwin“s groundbreaking theory of evolution. During their research, scientists discovered that Solanum pennellii from the archipelago”s younger western islands were producing alkaloids that had not been documented in modern tomatoes. This was in stark contrast to their counterparts on the older eastern islands, which had developed a more contemporary defense mechanism.
According to Adam Jozwiak, a molecular biochemist at the University of California, Riverside, who contributed to the study, this reversal suggests that the younger plants are not simply lagging behind in evolutionary terms but may be reverting to an ancestral state in response to environmental pressures. “Nature is very flexible, and it”s not the way we thought—everything doesn”t just go forward,” Jozwiak explained. The findings were published in June in Nature Communications.
While the appearance of the western tomatoes differed slightly—exhibiting purplish hues and darker vines—the most significant differences were found at the molecular level. In analyzing over 30 tomato samples, researchers noted that the western Solanum pennellii had a molecular signature akin to that of eggplants, which share a common ancestor with tomatoes. Unlike modern tomatoes, which have lost the ability to produce eggplant alkaloids, the western varieties appeared to have re-evolved or “de-evolved” to exhibit this ancestral gene.
This reactivation of ancient defenses in the tomatoes could have broader implications. By studying these compounds and understanding the reasons behind this genetic reversion, scientists might be able to develop improved crops, more effective pesticides, or even new medical applications. Jozwiak emphasized the potential benefits of this research, which could enhance our understanding of evolution across various species, including humans.
The origins of Solanum pennellii trace back to South America, likely arriving in the Galapagos through birds that transported its seeds one to two million years ago, prior to the formation of the younger islands due to volcanic activity. While the exact timing of the tomatoes” arrival on these islands remains uncertain, their evolution likely has occurred within the last half million years, coinciding with the emergence of the youngest islands.
The environments of the eastern islands are more stable and biologically diverse, while the younger islands present harsher conditions with less developed soil. The toxic alkaloids from the reactivated ancient genes not only help deter predators but may also assist the plants in nutrient absorption and disease protection, according to Jozwiak.
Research has shown that a simple alteration in the amino acid composition allowed the tomatoes to revert to their ancestral characteristics. To explore this further, researchers genetically modified tobacco plants to replicate these ancestral traits and confirm their functionality. However, additional studies are necessary to determine the advantages of this transformation and the reasons behind the reversion.
According to Anurag Agrawal, an evolutionary ecologist and professor at Cornell University, the case of Solanum pennellii highlights how plant chemistry can diversify in response to varying environmental conditions. He noted that the concept of reverse evolution is not particularly surprising, as evolution is often a process of tinkering rather than a straightforward progression. Examples include the loss of eyesight in cave-dwelling animals and the flightlessness of birds that once had flying ancestors.
Further investigations, including experiments to ascertain the timing and circumstances of these evolutionary changes, will be essential to validate the reasons behind this genetic reversion. While the high concentrations of alkaloids are not safe for human consumption, the wild tomatoes currently pose no health risks, as they are not cultivated for that purpose. Jozwiak expressed interest in returning to the islands to uncover additional insights into these plants and their interactions within their ecosystem.
While species developing island-specific traits is not uncommon—an observation made by Darwin regarding the varied beak shapes of finches—the term “reverse evolution” can be contentious within evolutionary biology, as it suggests a backward trajectory that contradicts the very nature of evolution, which lacks a predetermined goal. Eric Haag, a biology professor at the University of Maryland, noted that this research may challenge Dollo”s Law, which posits that lost traits are unlikely to be regained in the same form.
Despite the complexities of this case, the reemergence of ancient genes in Solanum pennellii opens up discussions about the flexibility of evolution. Jozwiak suggested that by recognizing this flexibility, scientists may discover instances of similar reversion in other species, including the potential for humans to exhibit characteristics reminiscent of their ancestral genes over time.
In summary, the findings related to Solanum pennellii not only challenge traditional views on evolution but also highlight the intricate dynamics of adaptation and survival in changing environments.
