Before you dream of 4 fingered hands, stop and consider with fewer fingers counting would have been more difficult in the old, old days, and things would probably have progressed a bit slower! :)
Not necessarily ... we use base 10 because we have 10 fingers, but that's not the only choice humans could've made.
Geometry could've played a role ... angle degrees aren't base 10, which makes measurements of angles / time awkward.
Mayas used base 20.
Babylonians used base 60, which is very convenient for angles since it's also divisible with 3 and 4.
Of course, I don't think there were number systems that had a base not divisible by 5 (except those that were baseless), and this probably does have something to do with the number of our fingers.
But I think we would've been just fine with 4 fingers ... we would probably count our feet too ... and base 16 would've had been the norm.
I couldn't imagine what a baseless numbering system could be. A quick google showed that Roman numerals are baseless. I always assumed they were a form of base10 and crazy shorthand.
I can't imagine what would be like to live with such a baseless numbering system ... life had to be much simpler for it to work. Like you didn't pay your taxes this month? Your possessions are confiscated or it's off with your head because calculating interest is too much work :)
They probably used counting boards, and specific units for measurement ... like they knew the size of a legion in their army and said "we have 3 legions, with 2 other joining, that's 5 legions" instead of ~ "we have 12600 men, 8400 more are joining, that's 21000 men".
Roman numerals are best thought of less as a numbering system (as we think of our modern system) but a semi-overgrown counting system. If you start out with hashmarks and sort of let it evolve, you can see pretty easily how they got to what they had. It's obviously limiting but not entirely stupid, when put into context.
