One of our body's natural hormones, melatonin, which is produced by our brains during the night, helps us to regulate sleep. However the pace of today's modern world, which leaves our brains in a constant state of overdrive, means that more and more of us are unable to produce this hormone naturally and are turning to the supplement version of melatonin.
Our understanding of melatonin is very much from the human perspective but where did it all begin? According to a study by the University of Heidelberg in Germany, animals have used melatonin in evolutionary development for years, going as far back as marine animal life, zooplankton.
Zooplankton's routine which sees them reach the surface of the water at dusk and dive back down at night, is their deep-rooted biological mechanism and may also go some way in explaining our own circadian rhythms. Light-sensitive cells found in the zooplankton brain were very closely matched with those found in the human pineal gland - the cells which produce melatonin and help to control our circadian rhythm.
Although the zooplankton's routine isn't exactly the same as sleep as we know it, the researchers were convinced that this is the closest thing they have found in simple organisms which emulates human sleep.