A fragment of some flatworms can reconstruct an entire animal. This ability of the planners seems straight out of a fantastic story. However, the family does not share the same power uniformly: in some species, a lost head does not reform.
Researchers associated with the Max Planck Society compared head regeneration in 36 species. Their study presented in 2023 distinguishes weak, limited or robust capabilities. It also examines the links between molecular signals, reproductive patterns, and these differences.
The result moves the question. It is no longer enough to ask how a worm remakes a head: it is necessary to understand why its cousin does not. Evolution may retain, modify or lose this ability. The formula “every piece of any worm gives back a worm” therefore erases precisely the differences that scientists seek to explain.
What we know
A 2023 study of 36 species; variable abilities, no generalization to all worms or fragments.
To go to the source
References consulted on September 21, 2026. Linked pages may be in another language.
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