Wild tomatoes on the Galápagos Islands may be providing scientists with an unprecedented look at “devolution” according to a new study.
Devolution, also known as reverse evolution, is the process in which species regain ancestral traits that were lost over millions of years. In a study published in Nature Communications, researchers have traced this phenomenon to a single enzyme that controls the chemical defenses of these plants, raising the question as to whether evolutionary forces could turn back the clock in response to environmental pressures.
The Solanaceae, or nightshade family, is a diverse group of plants that includes tomatoes, potatoes, and eggplants. These plants produce steroidal glycoalkaloids (SGAs), toxic compounds that serve as natural defenses against pests and pathogens. The researchers focused on a protein called GAME8, which acts like a tiny factory worker inside plant cells. GAME8’s job is to help build up those SGAs, and it does this by making a small but important change to the shape of these molecules at a spot called C25. This spot can be arranged in two ways, a bit like mirror images, they are similar but opposite.
By looking at many different species in the tomato family, the scientists discovered that, long ago, the original GAME8 enzyme made SGAs in the “25R” shape, which is the form still found in eggplants. Over millions of years, as the tomato and potato branches of the family tree evolved, the GAME8 gene was copied and changed. These changes led to a new version of the enzyme that produced the “25S” shape, which is now common in tomatoes and potatoes. This switch in chemical shape became the dominant form in these plants, helping them adapt to their environments and possibly influencing how well they defend themselves against threats.
But in the Galápagos Islands, things seem to be undergoing a devolution.
The wild tomato species Solanum cheesmaniae, which is native to the Galápagos Islands, appears to be reversing this evolutionary trend. According to the study, researchers found that some populations of S. cheesmaniae, particularly those on the younger, western islands, are producing increasing amounts of the ancestral 25R SGA isomer, a chemical profile more closely resembling that of ancient relatives like eggplants than that of modern cultivated tomatoes.
Detailed genetic analysis revealed that this shift is driven by specific mutations in the GAME8 gene, which restore its ancestral function. In some populations, a single amino acid substitution is enough to change the enzyme’s stereospecificity, while in others, three substitutions are present, leading to a near-complete reversion to the ancestral state.
“It’s not something we usually expect,” said molecular biochemist and lead author Adam Jozwiak in a statement. “But here it is, happening in real time, on a volcanic island.”
The distribution of these chemical profiles across the Galápagos archipelago closely mirrors the geological ages of the islands. Populations on older, eastern islands produce almost exclusively the derived 25S isomer, while those on younger, western islands produce much higher levels of the 25R isomer. This pattern suggests that local environmental conditions like soil, climate, or herbivore communities may be favoring the re-emergence of the ancestral chemical defense in certain habitats.
“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.”
The reason being is that “devolution” is a pretty hot button issue.
Dollo’s Law, named for Belgian scientist Louis Dollo, posits that complex traits lost in evolution cannot be regained in exactly the same way. Some scientists argue that what appears to be reversal is often the reactivation of dormant genetic pathways rather than a true recreation of lost complexity. In other words, what looks like “devolution” is really just evolution as older traits show back up because they become useful again.
Additionally, uncertainties in evolutionary trees and definitions of trait complexity can make it difficult to prove genuine reversals. Despite this, Jozwiak argues that a genuine reversal is exactly what happened, and that these tomatoes are looping back to ancestral forms.
The study proposes that the 25R SGA may offer a selective advantage under the unique ecological pressures found on the younger islands, driving natural selection to “rewind” the enzyme’s evolution.
To confirm the role of GAME8 in this process, the team performed functional assays by expressing both modern and ancestral versions of the enzyme in model plants. They found that the presence of the ancestral amino acid sequence reliably led to the production of the 25R isomer, while the modern sequence produced the 25S form. This demonstrates not only the molecular mechanism behind the reversal but also the flexibility of plant metabolic pathways in adapting to environmental change.
The findings from the study challenge the traditional notion that evolution is always a one-way process toward increasing complexity or specialization. Instead, it seems to show that lineages can, under certain circumstances, regain lost traits when those traits become advantageous again.
Beyond its implications of devolution for evolutionary theory, the study also provides practical insights for agriculture and plant breeding. Understanding how enzymes like GAME8 control the chemical defenses of crops could inform efforts to enhance pest resistance or reduce toxicity in food plants. It also raises questions about how other species might be using similar molecular devolution to adapt to rapid environmental changes, such as those brought about by climate change.
MJ Banias covers space, security, and technology with The Debrief. You can email him at mj@thedebrief.org or follow him on Twitter @mjbanias.