Every animal species carefully studied to date sleeps, or engages in something remarkably like it. This includes insects, such as flies, bees, cockroaches, and scorpions;I fish, from small perch to the largest sharks;II amphibians, such as frogs; and reptiles, such as turtles, Komodo dragons, and chameleons. Ascend the evolutionary ladder further and we find that all types of birds and mammals sleep: from shrews to parrots, kangaroos, polar bears, bats, and, of course, we humans. Even invertebrates, such as primordial mollusks and echinoderms, and even very primitive worms, enjoy periods of
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