Oi! I DO exist in this world, you know!
The latest edition of Nature, the prestigious scientific journal may have an answer for the question: 'Ever wondered why reindeers go round the world with Santa Claus without jet-lags?'. A group of researchers from Normay reported on this in the Nature's 22nd December's Edition in Brief Communcations have this to say :
Animals and plants have developed an internal biological clock that uses the light/dark cycle of day and night to synchronize daily rhythms in behaviour and physiological function. Is this circadian rhythm simply an adaptation to make good use of light and dark, or is a daily cycle of activity important to the proper function of an organism? The behaviour of reindeer living at high latitudes above the Arctic Circle provides an answer. Here the Sun neither sets in summer nor rises in winter. In these conditions reindeer lose daily rhythmic activity completely. For herbivores in polar regions at least, there is little selective advantage in maintaining circadian organization.
In laymans' term, all animals and plants have body clocks to tell us when it should be morning and when it should be