I heard all about this. See, I was a small arms repairman in the army, but before that was MOS 69X, which is Extraterrestrial Alien Technology Specialist. Anyway, it was my job to assess the technology discovered from various alien spacecraft that crashed on Earth. As it turns out, Earth is approximately the equivalent in the universe of Interstate 40 between Barstow and Needles. So, when aliens lost oil pressure in their spacecraft, they crash landed here because there werem't any intersteller gas stations hereabouts and AAA (Alien Assistance Association) doesn't serve this region and won't send a tow-UFO. So, these poor saps were stuck here. Some of them, however, became prominant actresses, but I can't tell you who they are---it's classified information.
Anyway, according to the alien equivalent of Reader's Digest magazine, Earth people drew one-sided people because at the dawn of time, an alien spacecraft had stopped at Earth to try and see if there was a Stuckey's here yet and accidently dropped a deck of playing cards when one opened the door to relieve himself. Some humans picked those up and copied the drawings of the face cards in all paintings since it was a big fad at the time to copy stuff (no one had yet invented the hula hoop, Rubic's Cube, or hackey-sack yet, see.) The alien playing cards are the same cards we use today, passed to us through time by their forgetfulness. Those face cards are depictions of the inhabitants of a planet of two-dimensional people that all walk like crabs and use parlor games instead of war to decide strategic matters on their planet. (Unfortunately, the losers in the game are summarily executed slowly with vegetable peelers while being forced to viewing of re-runs of their planet's equivalent of Love, American Style played on endless loops.) This is how human art became what it was until some enterprising artist discovered some nifty mushrooms.
This is the truth.
