As a Planarian, Marie Antoinette Would Have Survived the Guillotine
A planarian flatworm can be immortal. If you chop its head, it grows a new one. In contrast, the last queen of France, Marie Antoinette, had died at age 38 on October 16, 1793 after being executed on the guillotine during the French Revolution. If Marie Antoinette had benefited from planarian physiology, she would have regenerated a new head and survived the guillotine.
Planaria could have survived for 400 million years since they emerged on Earth. As such, they can serve as exceptional astronauts, who live through the billions of years it takes a spacecraft like Voyager to cross the entire Milky-Way galaxy. Interstellar journeys of planaria-like passengers allow for the direct transfer of life among the stars, even at the low speeds attainable by chemical propulsion or gravity assists, as long as the passengers have sufficient food and protection from cosmic-rays inside the enclosure that carries them.
Planaria are asexual flatworms with a head containing a brain, and a tail. If they are cared for, they live indefinitely. They reproduce by splitting in half. Planaria were known for a century to be immortal under the edge of a knife, with the ability to regenerate a complete organism even when their body is cut to as many as 279 small pieces. New tissues grow thanks to stem cells that can create all the various cell types. These stem cells are called neoblasts, constituting more than a fifth of the cells in the adult animal. They replace older cells, while existing tissue is remodeled to restore symmetry and proportion of a new planarian that grows from a piece of a cut-up predecessor.
The laboratory of Michael Levin at Tufts University demonstrated that some memory of past events is preserved in the new brain that a planarian grows. That memory is stored through electric signals in the planarian body, which can also be programmed externally. This suggests that the planarian body keeps memory of its entire life history and its qualities are not associated only with its DNA but also with the ability of its functions to be programmed through the memory of environmentally-induced mutations. Its survival algorithm is optimized for longevity and competency with a lot of junk DNA that is of secondary significance.
Planarian flatworms possess rich behavioral capabilities that include sensing of a wide range of environmental signals including chemicals, gravity, and gamma-radiation. Planaria have a brain but their entire body exhibits robust decision-making even when it is cut to pieces. Amputated fragments of planaria regenerate a complete worm, growing precisely what is missing with events at the wound edge coordinated tightly with body-wide remodeling of the intact tissue to ensure that a perfectly proportioned animal results within about a week after the cut. Every piece of a planarian is able to grow and remodel towards the large-scale pattern of its species, stopping precisely when that target morphology is reached.
The body of a starving planarian shrinks, and well-fed planaria grow while maintaining correct body proportions. While single cells within the planarian body die within about a month, the animal regenerates tissues continuously. As a result, planaria maintain life-long functional health and repair damages with impressive cognitive abilities as they learn from the environment and transfer information between the body and the brain. Planaria do not have cancer as they reprogram cancerous tissue while regenerating.
These remarkable animals show that biological systems can be immortal and compensate for damages associated with aging. Very little is known about how planaria regenerate and why they live forever. From fertilization to around 18 months, planarians, like mammals, show signs of decline, including the loss of neurons, muscle and diminished fertility. One sign of aging involves changes in their eyes over time. When the older planaria head is removed, the animal generates a new head with normal eyes. Planaria that had undergone regeneration have improved fertility as well as renewed physiological performance when compared to older planaria. Planaria have mechanisms to support longevity and healing even at old ages.
So far, no human artifacts came close to reproducing planarian capabilities. But further scientific studies might enable us to reverse-engineer and replicate these amazing qualities. Could the future of AI-assisted medicine enable humans to regenerate organs and avoid the devastating fate of Marie Antoinette? If so, interstellar travel might be possible for immortal passengers using current propulsion technologies.
One way to figure out if this futuristic feat is scientifically feasible is to search for extraterrestrial civilizations that developed such capabilities. The search for interstellar visitors defines the scientific goal of the Galileo Project. Coincidentally, our brilliant new manager, Zhenia Shmeleva, is also an active researcher in Michael Levin’s laboratory — where pioneering studies on planaria are conducted.
Yesterday, a short documentary was published by Bloomberg News about the first Galileo Observatory in Massachusetts. Our research team is currently assembling additional observatories in Pennsylvania and Nevada. Time will tell whether one of the Galileo observatories will discover interstellar enclosures that protect immortal organisms with the qualities of planaria.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
