In their research article "Identification of SLEEPLESS, a sleep-promoting factor" (18 July, p. 372), K. Koh et al. note that "[s]leep is an essential process conserved from flies to humans." This is not quite true. Many piscine species are active continuously without sleep (1), including species of marine and freshwater fishes in which schooling-swimming synchronously in polarized groups (2)-is fully developed (3).
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