Why are dreams of flying so common when it is so alien to us?

The long-running series in which readers answer other readers' questions on subjects ranging from trivial flights of fancy to profound scientific concepts

Dreaming that one can levitate or even fly seem to be near universal. Can anyone throw light on why something that presumably cannot have any basis in our evolutionary past should be so common to our unconscious selves? For me at least, when I have such dreams they always seem completely real (though my dreaming self is always suprised at discovering the ability).

Francis Blake, London N17