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Here’s what you’ll learn when you read this story:
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Evolution is often portrayed as stepping toward ever-greater complexity, but the natural world is filled with examples of organisms actually reverting back to a previous evolutionary state.
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A new study examines this process in progress with tomato plants in Galápagos, finding that plants on the newer, western islands have developed alkaloids similar to eggplant relatives millions of years ago compared to modern tomato plants.
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It’s possible these plants developed this strategy because the newer islands are barren and less biologically diverse, so the ancient molecule might provide better protection in such a harsh environment.
The famous ape-to-man illustration, known as The March of Progress, depicts evolution as a one-way street toward evolutionary perfection—but nature isn’t always so simple.
Many organisms have displayed what appears to be “reverse evolution,” or regression, where ancient attributes of past ancestors seem to reappear down the evolutionary line. Cave fish, for example, will lose eyesight and return to a state similar to a previous ancestor that lacked this visual organ, but the argument remains whether this is reverse evolution or simply the ending of an evolutionary pathway that creates a vestigial organ.
Of course, complex animals are not the only ones that appear to rewind the evolutionary clock. A new study in Nature Communications, led by scientists at University of California (UC) Riverside, analyzed species of tomato in the Solanaceae family, comparing populations from both eastern and western islands of the Galápagos—that famous Pacific island chain that inspired Charles Darwin’s evolutionary theory nearly 200 years ago.
The team specifically analyzed the tomato’s alkaloids, a bitter molecule that acts as a kind of pesticide to deter would-be predators and fungi. On the eastern islands, the tomatoes exhibited alkaloids similar to modern tomatoes, but on the western islands—which are geologically younger than the eastern ones—the tomatoes exhibited changes in four amino acids in the enzyme that makes these alkaloid molecules. They found this simple change caused the tomatoes to create alkaloids more similar to eggplant relatives from millions of years ago, seemingly reversing evolution.
“It’s not something we usually expect, but here it is, happening in real time, on a volcanic island,” UC Riverside’s Adam Jozwiak, lead author of the study, said in a press statement. “Our group has been working hard to characterize the steps involved in alkaloid synthesis, so that we can try and control it.”
However, this “reverse” wasn’t a spontaneous event. The researchers theorize that the cause of this evolutionary quirk could be traced to the new, western islands themselves. While the eastern islands are millions of years old, the western ones are only hundreds of thousands of years old and are still forming today. This means these islands contain less biological diversity as well as more barren soil. This more ancient landscape may have pushed the tomato to then adopt a more ancient survival strategy.
“It could be that the ancestral molecule provides better defense in the harsher western conditions,” Jozwiak says. “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.”
Whether organisms experience “reverse” evolution could largely be chalked up to semantics. With both cave fish and Galápagos tomatoes, evolution did its usual work of making life fit for the conditions at hand. Usually that means improving into ever greater complexity, and at other, less often times, it means reverting back to a golden oldie.
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