To treat this as "obvious" rather than "interesting" is an epistemic error. In particular, any ancient counting system could be given a similar anatomical anal

To treat this as "obvious" rather than "interesting" is an epistemic error. In particular, any ancient counting system could be given a similar anatomical analysis. Base 30? Well, it's only the first two knuckles that are easy to bend. Base 14? Clearly the major joints were being used for counting (because counting, not communication was the issue: people had words for communication and didn't need hand gestures). Base 8? Again, the first two knuckles, multiply both hands to get 64... so maybe that would be base 64? Simply because you can give an account of what people actually used is no proof of explanation: you also have to given an account of why what was not used was not used. Claiming it was because it was somehow less convenient than the system you suggest is not an explanation, but a classic example of begging the question (assuming the consequent.)