Wild Tomatoes in Galápagos Challenge Evolution’s Forward Path

In the Galápagos Islands, a wild tomato species is providing intriguing evidence that evolution may not always move forward. Researchers studying Solanum pennellii, a small tomato native to this unique archipelago, discovered that the plants on the younger western islands exhibit traits reminiscent of ancestral varieties not seen for millions of years. This finding suggests a phenomenon some are calling “reverse evolution.”

The research team, led by molecular biochemist Adam Jozwiak from the University of California, Riverside, initially focused on alkaloids—natural compounds that function as pesticides. During their analysis, they found that western island tomatoes were producing these compounds, which had seemingly vanished from modern tomatoes. This discovery was reported in June 2024 in the journal Nature Communications.

The team compared samples from the younger islands with those from the older eastern islands. They observed that tomatoes from the east had a modern defense system, while those from the west showed signs of reverting to ancestral traits. Jozwiak remarked, “It’s not very common to see reverse evolution,” emphasizing that environmental pressures may have prompted these tomatoes to revert to their ancestral state.

The physical appearance of the western plants differs slightly; they bear a purplish hue and darker vines compared to their eastern counterparts. However, the most significant differences were found at the molecular level. Analysis of over 30 tomato samples revealed that the western Solanum pennellii carried a molecular fingerprint resembling that of eggplants, another member of the nightshade family.

Modern tomatoes have lost the ability to produce eggplant alkaloids, yet these wild tomatoes appear to have re-evolved this trait. Jozwiak explained that understanding this molecular shift could lead to advancements in agriculture, including the development of enhanced crops and pesticides.

Solanum pennellii is believed to have originated in South America before reaching the Galápagos Islands via birds carrying seeds approximately 1 million to 2 million years ago. Jozwiak noted that the evolution of these plants must have occurred within the last 500,000 years, coinciding with the formation of the younger islands through volcanic activity. The stark environmental differences between the eastern and western islands—stable biodiversity versus a barren landscape—likely influenced this evolutionary divergence.

Molecular analysis revealed that a simple alteration in the amino acid composition enabled the plants to revert to earlier traits. To explore this further, the researchers genetically modified tobacco plants in a similar manner, confirming the production of these ancestral compounds. However, Jozwiak highlighted that more research is needed to fully understand the implications of this transformation.

The phenomenon of plants developing unique traits on islands is not new. Charles Darwin famously observed such variations during his visit to the Galápagos in 1835. Yet, the concept of “reverse evolution” remains contentious within evolutionary biology. Jozwiak pointed out that evolution is not typically viewed as a linear process, a sentiment echoed by evolutionary ecologist Anurag Agrawal from Cornell University, who stated, “Most evolutionary biologists would reject evolution as a forward process.”

Agrawal cited various examples, such as cave-dwelling animals losing eyesight or birds like penguins evolving from flying ancestors. He noted that these instances illustrate evolution’s tendency to take detours rather than strictly advance.

The study also poses questions regarding the implications of this reversal for evolutionary theory. Eric Haag, a biology professor at the University of Maryland, commented that the findings challenge Dollo’s Law, which claims lost traits cannot be regained in the same form. He remarked, “It appears the specific amino acid changes… in the Galápagos species are some of the same ones found in much more distant ancestors.”

While Jozwiak does not study human evolution directly, he suggests that viewing evolution as more flexible could reveal similar trends in other species, including humans. Instances of people born with rudimentary tails, a trait seen in primate ancestors over 25 million years ago, provide a fascinating example of retained evolutionary potential, according to research professor emeritus Brian Hall from Dalhousie University.

Despite the potential implications for human evolution, Hall cautioned against the term “reverse evolution,” arguing that it implies a return to an ancestral state, which is impossible. He described it instead as a “retention of evolutionary potential,” similar to horses that can occasionally exhibit traits from their ancestors.

Conversely, Beth Shapiro, a professor of ecology and evolutionary biology at the University of California, Santa Cruz, views the term as an engaging way to discuss evolution with the public. She noted that evolution is not directional but rather a response to changing environments, where rare ancestral gene variants can resurface.

The ongoing research into Solanum pennellii underscores the complexity of evolution and the need for further investigation. Jozwiak expressed hope to return to the Galápagos Islands to explore additional traits influenced by these ancestral molecules, including plant interactions with insects and their decomposition rates.

As scientists continue to unravel the mysteries of evolution, the case of the wild tomatoes in the Galápagos Islands serves as a compelling reminder of the intricate and sometimes unpredictable pathways that life can take.