You have probably picked up a dozen eggs at the store many times. But why do they come in cartons of 12 instead of eight, 10, or another number?
People have eaten bird eggs since prehistoric times, and chickens were first domesticated thousands of years ago in Southeast Asia. Eggs did not become mass-produced goods until the mid-1900s, when better sanitation, enclosures, and feeding methods allowed farmers to produce them throughout the year.
The practice of selling eggs by the dozen may be much older. No one knows exactly where it began, but the leading theory involves an old English coin called the shilling. For much of its history, one shilling was worth 12 pennies. The first shilling was minted in England in 1504, and the coin remained in use until 1971.
This system made a dozen eggs convenient to sell: one shilling could pay for 12 eggs without any change. The number 12 is also easy to divide into halves, thirds, or quarters, which made purchases simple to split. The custom later crossed the Atlantic and became common in America.
It is not a universal rule. In parts of Africa and India, eggs are still often sold one at a time, while shops in different countries may offer cartons of eight or 10. Still, the dozen has remained popular. Sometimes a handy old system simply sticks around.