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…