On the immortal hydra. Again

The long history of ideas about the most famous “immortal” (non-aging) organism, freshwater hydra, is shortly reviewed. Over the years this polyp has attracted the attention of naturalists interested in problems of aging and longevity. In recent years, this interest has abruptly increased with the accent on fine mechanisms providing an almost complete lack of aging in hydra. It is emphasized that hydra immortality is based on indefinite self-renewal capacity of its stem cells. It is this fact that allows the polyp to continuously replace the “outworn” cells of the organism, keeping all its characteristics unchanged for an almost unlimited time. It is concluded that the applicability of the data obtained in gerontological experiments on hydra to human being is, unfortunately, very limited because normal functioning of many important organs and tissues in highly developed organisms is determined by the presence of postmitotic cells (neurons, cardiomyocytes, etc.), which actually cannot be replaced.