The New York Times addresses what a recent research paper about the evolution of melatonin says about sleep.
To explore the evolution of sleep, scientists at the European Molecular Biology Laboratory in Germany study the activity of genes involved in making melatonin and other sleep-related molecules. Over the past few years, they’ve compared the activity of these genes in vertebrates like us with their activity in a distantly related invertebrate — a marine worm called Platynereis dumerilii.
The scientists studied the worms at an early stage, when they were ball-shaped 2-day-old larvae. The ocean swarms with juvenile animals like these. Many of them spend their nights near the ocean surface, feeding on algae and other bits of food. Then they spend the day at lower depths, where they can hide from predators and the sun’s ultraviolet rays.