The potential evolutionary significance of the pineal gland

Although during the early 20th century the pineal gland was considered to have littlefunctional significance, the activity of its secretory product, melatonin, has beenincreasingly appreciated during recent decades. Melatonin has a role in the sleep-wakecycle and recent studies have shown that it acutely enhances mating behaviour and libido.Since reproductive activity is obviously of primary importance for the survival of species, this could plausibly suggest a circadian control of mating behaviour. In this chapter, weargue that the coupling of mating behaviour to light-dark shifts by melatonin might haveinfluenced the survival of species, and this could throw fresh light on the evolutionarysignificance of the pineal gland.