http://www.nih.gov/news/health/dec2013/nichd-23a.htm

As a very ancient part of the endocrine system which also combats
malignancies, melatonin performs many functions in modern bodies.
Melatonin is a topic which comes up often on the FHL and FML with
sufficient melatonin being possibly important in delaying or avoiding
adrenal disease. Melatonin is produced in the body in darkness. It is
most disrupted by wavelengths of blue light, second most disrupted by
green light wavelengths, and least disrupted by amber wavelengths.

You can get a rough idea how old things like enzymes are from the
number of functions they perform currently, BTW, but this work
confirms it.

[Posted in FML 8000]