In response to
Pretzellogic: Ah, but they have a glaring phenotypical difference:
Ms. Pac-man has a little bow on her head!
I propose the theory that Pac-beings reproduce via a form of pollenisation that requires humans as the carrier. Think about it. Pac-Man and Ms. Pac-Man always inhabit seperate arcade cabinets. Therefore they cannot come into physical contact. A player comes along, and responding to the game's attract sequence (similar in principle to the colourful flowers and courtship displays found elsewhere in nature) and inserts a coin into the machine. On entering the workings of the machine, this coin will be charged with Pac-Man sex cells. These are released when the Pac-Man dies. The score counter indicates the amount of nutrition that the 3 Pac-Men controlled by the player have accumulated from eating pills and ghosts, and this corresponds to the amount of sex cells they can produce (this is why the player is encouraged to acheive a high score).
Eventually all the coins will be removed from the machine and returned to circulation - however, only a few of those will make it back into a Ms. Pac-Man cabinet (this is why Pac-Man is such an addicitive game - to extract the maximum number of coins from the human carrier). We can follow this reproduction process statistically. New Pac-Men and Ms. Pac-Men only ever appear from the machine when coins are put in. If the amount of coins decreases, the cabinet is removed from the arcade - that Pac-Ecosystem has failed.
Maybe this unsatisfactory method of reproduction explains why Pac-Man is perpetually popping pills.