What Happens If You Split A Garden Worm In Half

Chop Up a Worm. It Will Regenerate. Scientists Figured Out Why.

Slice a three-banded panther worm in half or thirds and within eight days you'll have separate fully functioning worms.

Credit... Kathleen Mazza-Curll and Mansi Srivastava/Whitehead Institute

March 20, 2019

An essential rite of passage for many an otherwise nonviolent child involves cutting an earthworm down the middle and watching as the two halves squirm. One half — the one with the brain — will typically grow into a full worm.

Scientists have now identified the master control gene responsible for that regrowth in one particularly hardy type of worm. How hardy? Chop the three-banded panther worm in halves or thirds — either crosswise or diagonally — and each segment will regenerate just fine, said Mansi Srivastava, a professor of organismic and evolutionary biology at Harvard University. Within eight days, you'll have two or three fully functioning new worms, mouth, brain and all.

"It's hard to kill them," she said.

Dr. Srivastava and her co-authors published a paper Friday outlining their genetic discovery. The process is known as "full-body regeneration," and the term has captured the imagination of many individuals ready for a fresh start or second self.

"I'll get a new body right now!!" one person wrote in a lively Reddit thread about the finding, adding "I knew it was coming!!" Another posted: "Two of me working together and sharing our stuff? Count me in!"

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Headlines suggesting that the scientists have found the DNA switch that could lead to human limb regrowth have fueled hopes that the discovery will offer precisely that. Unfortunately, no one is growing a new arm or getting a second body with the help of marine worm DNA anytime soon, said Peter W. Reddien, a biologist with M.I.T.'s Whitehead Institute for Biomedical Research and another author of the paper.

But he added that he didn't totally blame people for getting carried away because his field truly is stranger than fiction.

"You can damage large amounts of the heart muscle of a fish and the heart will come back," he said. "You can remove the jaw or even the entire head and some animals will grow it back. It's amazing."

What's accurate in this particular case is that a master control gene known as E.G.R. — or early growth response — is present in many kinds of organisms, including humans. An injury that pierces skin often activates it, he said. But activation is just one small piece of a larger puzzle.

"It's like a hand playing the keyboard," Dr. Reddien said. "Something has to decide in cells which notes to play; which genes to turn on. There are some genes whose function it is to tell other genes whether to be on or off. This is one of those kinds of genes."

Before this study, scientists suspected that E.G.R. was involved in initiating regeneration in the three-banded panther worm, Dr. Srivastava said, but they had not proved it. In order to do so, first they had to sequence their subjects' entire genome.

Once that was complete, researchers sliced hundreds of the worms, which are about the length of a Tic Tac, in half with a tiny knife. They then monitored the opening and closing of DNA all over the worms' genome at various intervals during the process of regeneration.

"The question of when regeneration is complete is a philosophical one," Dr. Srivastava said.

But there are concrete points that can be tracked — the emergence of a mouth and the creation of a brain, for example.

Once the scientists were quite certain that E.G.R. was connected to all this activity, they tested their hypothesis by disabling that gene's function, using a popular interference method. And indeed, while the worms in the control group were swimming and eating again at Day 8, these worms failed to grow or move.

So nine years after Dr. Srivastava first collected three-banded panther worms from a marine pond in Bermuda, she had figured out how one worm could become two or three, outside the traditional processes of reproduction.

As to whether worms' regeneration abilities could ever help humans heal, she's open-minded. "The way biomedical research is going, it will probably happen," she said. "I just don't think it will happen in the next 10 years."