The sleeping pattern of humans may have evolved in the ocean millions of years ago, suggests a new study.

Researchers at the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany suggest that a hormone called melatonin governs jet lags and sleep patterns in humans. The hormone is also important as it is essential to sustain our daily rhythm. Scientists claim that melatonin also directs the regular nightly migration from the surface to deep ocean waters in the plankton species.

The scientists indicate that almost all animals have melatonin and the hormone is well-known in controlling activity patterns in vertebrates.

Detlev Arendt, the lead researcher of the study, examined marine ragworm Platynereis dumerilii. The larvae of the worm are supposed to have the biggest migration on the planet in terms of migration from surface to deep oceans. They migrate from the ocean surface at dusk and swim up in the day.

The researchers were able to examine the brain of the larva and found that a specialized group of neurons respond to melatonin. These neurons change a lot from day to night. The researchers revealed that the melatonin production during the night makes changes to the neurons, helping the larvae to sink to deep oceans at night. When melatonin is not produced, the larva can swim upwards.

"We found that a group of multitasking cells in the brains of these larvae that sense light also run an internal clock and make melatonin at night," says Arendt.

The scientists think that the hormone is actually a message produced by the cells at night, regulating the neurons' activity and ultimately driving the rhythmic behavior during night and day.

The scientists revealed that when the larvae were exposed to melatonin during daytime, they showed behavior associated with nighttime "as if they were jet lagged."

The scientists strongly believe that the "larva's nightly migration have evolutionary relatives in the human brain." Cells responsible for controlling wakefulness and the rhythms of sleep may have evolved millions of years ago in the ocean.

The researchers suggest that the findings of the study are important as it can to explain the step-by-step evolutionary origin of the key functions of human brain.

Check out a short video clip explaining the role of melatonin in the larvae.