Why are eggs sold in dozen?

Eggs

Normally we count with our eight fingers and two thumbs when we don't have paper handy. But a different method of counting uses the knuckles of each of the fingers (excluding thumbs). That gives you a count of twelve on each hand, for a total of twenty-four. It's also thought that this is why we have twelve hours in each half of the day, and twelve months in the year. This method of counting was heavily used by the Phoenicians. The other reason that 12 has significance is that it's divisible by 6,4,3, and 2. The next highest number that has four divisors besides 1 and itself is 18 (and there are none lower).

Now, given all that, what's the reason that eggs are sold by the dozen? Well, the first answer would be that it's tradition. The second answer would be that a dozen eggs is about what the average house would go through in day or two days or simply before they go bad. That depends on the house of course, and how often a trip to the market would be made.* The third answer is that 12 is more easily divisible, so baking recipes (the primary use for eggs when you aren't eating them plain) can be calculated faster, and you're less likely to be left with an amount of eggs that isn't easy to split (5 or 7).

That's my guesswork anyway.

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