What does a car pool, a gene pool or a typing pool have to do with chickens? Mark Forsyth tells the story in his book The Etymologicon. In medieval France, it seems, gamblers would sometimes bet on who could be the first to hit a chicken with a stone. It was a cruel game, but perhaps not as cruel as chicken fights and dog fights, which still attract gamblers in some areas.
Had these gamblers been English speakers, they would have called this a game of chicken. Instead they called it poule, which is the French word for chicken. The winner won the pot, or what they called the jeu de poule. The term spread to cards and other forms of gambling, where the money at stake became known as the poule. When English visitors returned home, they took the word with them, but they spelled it pool. Billiards became known as pool because players commonly bet on the game.
If gamblers could pool their money, then why couldn't others pool other kinds of things, such as genes and typists?