Sleeping beauties of the animal kingdom show how life and memory persist.

Researchers report that organisms from permafrost, deserts and hibernating mammals can enter reversible dormant states and later revive, and some studies find learned behaviours and biological information persist through long dormancy.

Organisms found in Siberian permafrost, the Atacama Desert, Arctic burrows and Polish forests can enter deep dormant states and later return to activity. These states, often called cryptobiosis or hibernation, involve arrested metabolism and large-scale cellular change. Scientists are studying what is preserved during dormancy and how organisms recover. The question centers on which forms of biological information survive suspension and how that influences recovery. Key facts: - Researchers in Pushchino, Russia revived bdelloid rotifers frozen in Siberian permafrost for more than 24,000 years, reported as surviving in a state of cryptobiosis. - Microscopic animals such as rotifers, tardigrades and brine shrimp use sugars and stress proteins to preserve cellular integrity during long dormancy. - In Chile’s Atacama Desert, bacterial communities found under dry soil were reported to revive and reproduce when moisture returned, and investigators suggested such dormancy could span hundreds or thousands of years. - Arctic ground squirrels lower their body temperature and undergo neuronal pruning during hibernation, yet studies show they retain pre-hibernation recognition and learned behaviours on emergence. - Experiments at the Polish Academy of Sciences found bats trained on a maze before hibernation navigated it with similar accuracy after months of hibernation, suggesting an unidentified neuroprotective mechanism. - The 2020 discovery of the parasite Henneguya salminicola, described as the first known animal to have abandoned the need for oxygen, challenges assumptions about oxygen as a universal requirement for animal life. Summary: These observations challenge the view that ongoing metabolism and continuous neural activity are strictly required for preserving memory and developmental information. The article describes evidence that information may be distributed in cellular organization, epigenetic marks and body tissues, and notes potential implications for medicine, regenerative biology and the search for life beyond Earth. Undetermined at this time.