To kick off the First Joke Thread of 2010, we have the following:
"The Giant"
One day a planet was discovered out Antares way whose sole inhabitant was an enormous humanoid, three miles high. At first it was mistaken for an immense statue left by some vanished race of giants, for it sat motionless on a yellow plain, exhibiting no outward sign of life. It had legs, but it never rose to walk on them. It had a mouth, but never ate or spoke. It had what appeared to be a perfectly functional brain, the size of a condominium, but the organ lay dormant, electrochemical activity at a standstill. Yet it lived.
This puzzled the scientists, who tried everything they can think of to get some sign of life from the behemoth -- in vain. It just sat, motionless and seemingly thoughtless, until one day a xenobiologist, frustrated beyond endurance, screamed, "How could evolution give legs, mouth, and brain to a creature that doesn't use them?"
It happened that he was the first one to ask a direct question in the thing's presence. It rose with a thunderous rumble to its full height, scattering the clouds, thought for a second, boomed "IT COULDN'T", and squatted down again.
"My God," exclaimed the xenobiologist, "of course! It only stands to reason!"