Nestled in your brain is a biological clock that pretty much corresponds with the 24 hour clock of a day.
This clock is composed of a circuit of neurons that, in effect, rewind each new day in response to light and other stimuli. Your environment regulates your biological clock, and your biological clock regulates a whole host of your physical functions, from sleeping and waking to body temperature to cardiac output.
Now what if you were told that your body isn't regulated by one clock, but two? Does the very idea make you dizzy?
Scientists have believed for some time that fruit flies may run on two different body clocks because they have two peaks in their activity, one in the morning and one in the evening. There are several possible explanations for the two peaks, but one is that separate clocks govern each of the peaks. Now this theory has been confirmed.
The two clocks in the fruit fly occupy different positions in the brain and produce different signaling molecules. Relax, the clocks aren't competing structures. They're connected and under normal light conditions, they regulate one another. Scientists hypothesize that such a set-up may aid a body in responding to environmental factors such as seasonal changes in lightness and darkness.
The discovery is advancing understanding of general principles of the structure and function of neurons, including the various levels of communication between neurons.
What's more, there is evidence that mammals, including humans, may also possess dual clocks that communicate with one another. If so, however, the second clock has yet to be discovered in the human brain.