I feel bad making an unrelated comment because the topic is so interesting, but an interesting fact coincidentally related to two seperate points made is that it appears that chimps are actually better at subitizing (determining the size of a set without counting) than humans. Upon searching I didn't find any large studies, but the numbers I did find point towards that chimps can subitize sets up to a size of either 6 or 7 (compared to probably 5 for humans).