It is stated that the pineal gland produces the hormone melatonin, but almost exclusively at night. Normally, we grow sleepy when levels of melatonin are high (night time) and awaken when they are low (daytime). This pineally controlled cycle, of course, is called our circadian rhythm. In fish and amphibians, the pineal gland is located near the surface of the skin...rather a third eye that detects light on its own. In mammals however, it is locaded in the third ventricle of the brain, depending on nerve signals from they eyes to detect light. Melatonin and the pineal gland are why some people experience "jet lag" and SAD (seasonal affective disorder) Melatonin itself is produced to inhibit growth of reproductive organs/sexual desire.

According to biological science, people can grow very ill (jet lag, (SAD) from having too high a melatonin level, but that this could be cured by exposure to bright light. Could we not, assume from this that a person who was naturally low on melatonin be generally healthier to avoid light? This would also explain why vampiric people tend to be very sexually oriented...the hormone inhibits those feelings is deficient.

Oddy enough, there is another sleep inducing chemical in the brain called seratonin. The difference? Seratonin is made in response to light. Technically, because of the seratonin, most people should sleep in the day, but have become night-sleepers through evolution. Scientists claim that "night-owls" and nocturnal persons have simply "reverted". Besides making people sleepy, seratonin is the hormone that greatly effects mood and emotions. Insuficient, imbalanced, or poorly distributed seratonin is the most common cause for most forms of clinical depression.

In theory, (and half in jest) it could be said that a person with an imbalance in seratonin (too much), and a deficiency in melatonin might become a moody and often depressed, nocturnal sex fiend. Youch!

www.angelfire.com/pe/MitochondriaEve/pineal.html