Tomatoes fighting evolution? Scientists find tomatoes evolving backward

Charles Darwin’s theory of evolution states that all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual’s ability to compete, survive, and reproduce.

But ever since Darwin released his concept in his On the Origin of Species paper in November 1859, scientists have debated whether the mechanism can work the other way - whether evolution is reversible.

De-evolution, ie. “reverse evolution” is the idea that just as species evolve, they can also regress, reverting to a more primitive form or state over time.

Wild tomatoes go back in time

The debate continues, but a new study by scientists at University of California (UC) Riverside which was published last month, looks into the a possible case of de-evolution in wild-growing tomatoes in the Galápagos islands.

Researchers noticed that one sample of tomatoes studied showed unusual properties which could be a sign that they are in a process of regressing to a more primitive genetic state.

The key finding concerned mutations in steroidal alkaloids, nitrogen-containing compounds which are produced by a large variety of organisms, including plants, as a defense mechanism - their bitter taste acts as a kind of pesticide, deterring predators and fungi.

Ancestral alkaloid related to eggplants

The team analyzed more than 30 tomato samples collected from the eastern and western Galápagos islands. The plants collected from the eastern islands produced the same steroidal glycoalkaloids (SGAs) found in modern cultivated tomatoes (25S). However, on the western islands, tomatoes were producing alkaloids with a different configuration (25R), an isomer related to the same Solanum species but produced by eggplant.

The study showed that the tomatoes on the younger, western islands flipped their molecular configuration to an older, ancestral version. Researchers discovered this was related to the different climatic and geological conditions on the different islands.

Tomatoes on the older, eastern islands, which are climatically more stable and biologically diverse, made modern alkaloids (25S) while the western island crop, reverted to an older molecular makeup due to the harsher conditions, fertility of the soil... etc.

“It could be that the ancestral molecule provides better defense in the harsher western conditions,” Adam Jozwiak, UC Riverside molecular biochemist explained. “Some people don’t believe in this, but the genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It happened. If you change just a few amino acids, you can get a completely different molecule. That knowledge could help us engineer new medicines, design better pest resistance, or even make less toxic produce. But first, we have to understand how nature does it. This study is one step toward that.”

Reverse evolution and environment

While the scientific world jury remains out on how reverse evolution works in nature and whether evolved species can revert to a previous state or, the wild tomatoes on Galápagos at least give us a clue that environment plays a big part in the process.

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