Retro tomatoes: a species of the plant is evolving backward

Some tomatoes have evolved to possess the characteristics of their ancestors. While it is rare, there have been instances of species displaying traits from further back in evolution. But for the first time, scientists have now been able to prove it through genetic evidence. And there's potential for similar evolutionary changes in the future as the environment changes, even in humans.

Blast from the past

Wild tomatoes on the Galápagos Islands are using chemical defenses that are reminiscent of their ancestors, according to a study published in the journal Nature Communications. The flowering plants have "quietly started making a toxic molecular cocktail that hasn't been seen in millions of years, one that resembles compounds found in eggplant, not the modern tomato," said scientists in a statement about the study.

Tomatoes are nightshades, like potatoes and eggplants, and nightshades produce alkaloids, which are "bitter toxins that protect the plants against predation," said the BBC. Researchers discovered that tomatoes "on the older eastern islands produced alkaloids found in modern cultivated tomatoes," while tomato plants "on the younger western isles were making unique alkaloids." And the latter alkaloids were largely produced by ancestral tomatoes.

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"Some people don't believe in this," said Adam Jozwiak, a molecular biochemist at the University of California, Riverside, and the lead author of the study, in the statement. But the "genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It happened."

Researchers deemed the phenomenon a possible case of "reverse evolution." Usually, evolution "moves forward, adapting organisms to current conditions," said Earth.com. The "idea that it can loop back and restore long-lost traits isn't just controversial — it's considered highly unlikely."

The case of the tomatoes is especially interesting, as the plants developed the ancestral trait using the same genetic route the ancestral plants did. The researchers pinpointed a specific enzyme responsible for the tomatoes' alkaloid production and "confirmed its ancient roots," said ScienceAlert. Species can sometimes "re-acquire features similar to those of their ancestors," said the statement, but "doing so through the exact same genetic pathways is rare and difficult to prove."

Back to the future

Reverting to an ancestral genetic trait could be a response to the harsh Galápagos environment. "The plants may be responding to an environment that more closely resembles what their ancestors faced," Jozwiak said to the BBC. The geography supports that claim. The eastern islands are "biologically diverse and more stable. Here, the tomatoes "produced modern alkaloids," said IFLScience. On the other hand, the western islands, where the plants are producing the ancient alkaloids, are "younger, the landscape is more barren, and the soil less developed."

This phenomenon may not be exclusive to tomatoes. It has also been seen in snakes, fish and bacteria, though it's "rarely this clear or this chemically precise," said the statement.

This looks like evolution is "going backward." But what it really shows is the "amazing flexibility of evolutionary processes," said the BBC. And given the reality of climate change, other species may eventually go through similar processes. "I think it could happen to humans," said Jozwiak. "It wouldn't happen in a year or two but over time, maybe, if environmental conditions change enough."