The Corner on National Review Online |DOZENS
"DOZENS [John Derbyshire]
Rich: Why dozens instead of tens? I'm going to throw out some guesses here.
(1) In the days before Hindu-Arabic numerals made computation easy, everyday-size numbers (less than 1,000) were easier to handle -- especially to divide up -- if they were as 'round' as possible -- that is, had the largest possible range of different factors. Hence the popularity of 12 (which divides by 2, 3, 4, and 6) compared with 10 (which merely divides by 2 and 5). It was perhaps for similar reasons that the ancient Mesopotamians settled on 60 as the mainstay of their number system. The number 60 has an awesome array of factors: 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30.
(2) Ancient astronomy may also have been a factor. The earliest systems for organizing time took 360 as the number of days in a year (regarding the extra 5.2422 as an inconvenience to be conjured away with intercalary adjustments). Once you start doing arithmetic with 360, you are back in the world of 12 and 60 very quickly -- especially as there are, to a first approximation, 12 months in your 360-day year..."