Ferns Could Potentially Return To An Earlier, More Basic Form

Most people are familiar with Rudolph Zallinger’s illustration “The March of Progress” which depicts human evolution from the early primate ancestor Dryopithecus to modern Homo sapiens. While evolution is a captivating process, it doesn’t always move in a straight line as Zallinger’s image suggests.

The notion that evolution progresses in a one-way path from simple to more complex forms, each building permanently on the last, has been long-standing. According to paleontologist Louis Dollo’s law, once an organism develops a specialized trait, it doesn’t return to an earlier form.

New Research Challenges the One-Way View of Evolution

A recent study published in the journal Evolution is questioning the long-held belief that life evolves in only one direction. The research indicates that certain plants may be capable of “evolving backward,” meaning that specialized species can return to more primitive forms.

The study centers on the chain fern (Blechnaceae)., one of the planet’s oldest plant groups, dating back before the dinosaurs. Scientists from the University of Tennessee examined the fern’s reproductive methods and discovered that it still maintains two separate modes of reproduction.

Researchers discovered that some chain fern species are monomorphic, using a single type of leaf for both photosynthesis and spore production. In contrast, others exhibit dimorphism, a specialized strategy where separate leaf types handle reproduction and photosynthesis.

This variation in reproductive strategies adds a layer of complexity and provides a chance to test Dollo’s law. If evolution were strictly one-way, ferns that developed dimorphism wouldn’t revert to the simpler monomorphic form.

Fern Evolution

By analyzing over 118 species with the help of natural history collections and evolutionary modeling algorithms, researchers found that fern evolution is “neither stepwise nor irreversible.” Interestingly, they identified several cases where chain fern species evolved dimorphism but later reverted to the simpler monomorphic form.

To explain why chain ferns can reverse their evolutionary path, researchers propose that the absence of seeds in their reproductive process plays a key role. Unlike seed-producing plants, which may be locked into complex reproductive structures, ferns—lacking seeds—can more easily adapt their leaves into spore-producing forms suited to changing environments.

“Evolution has no finish line. There’s no final destination or ultimate form,” says Jacob S. Suissa, Assistant Professor at the University of Tennessee. “Our research indicates that not all reproductive specialization in plants is permanent. It may depend on how many layers of complexity have developed over time.”

Read the original article on: New Atlas

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