The Incredible Immortality of the Fresh-Water Hydra

An enduring episode of the KQED series “Deep Look” examines the hydra, a tiny, seemingly immortal organism that lives in tropical freshwaters. The hydra has neither eyes nor brain but does have a big mouth and an uncanny ability to regenerate every part of itself despite the most catastrophic injury. This due to its high multitude of stem cells.

Hydra are constantly regenerating their own bodies too, replacing all of their cells every 20 days. They can do that because roughly half of the cells in their bodies are stem cells,…Stem cells only make up a tiny percentage of our bodies And our stem cells degrade over time — that’s why we age. But a hydra can make near-perfect copies of its stem cells … basically forever.