Why is "Sleep in animals" trending?

Wikipedia Overview

Sleep is broadly considered a biological necessity in virtually all animals. The large majority of such taxa with documented sleep physiology are bilaterians, though there is increasing evidence of sleep or sleep-like states in non-bilaterians such as Cassiopea jellyfish and hydra, and sponges. The various criteria which biologists use to define sleep states have been observed in all other animal phyla, often with profound variation in function. In all of these taxa except sponges, regulation of sleep is documented to involve genes whose transcription oscillates with time, known as circadian or clock genes. These genes and the gene networks they regulate give rise to the internal circadian clock. The three categories of biological sleep schedules are diurnal, noctural, and crepuscular which characterize species whose waking periods mostly overlap with day, night, and twilight respectively. Specific sleep patterns and durations vary widely among and sometimes within sleeping species, with some sleeping or foregoing sleep for extended periods. Others, such as some porpoises, engaging in unihemispheric sleep where only one brain hemisphere sleeps at a time in order to maintain motion or homeostasis in marine environments.