Some notion of I as an individual being came first. Then I found a mate and two became one such that 1 could be divided into 2. And baby makes three, and 1 can be divided by three and four. Was it some form of share and share alike? A provider and a number of mouths to feed? A "we" divided further, as the both partners must have contributed, if not equally in production equally in what was required to maintain a life which isn't equal, but we shoot for it? Muscle mass verses reproductive capacities mass + what ever was needed?
How long have simple fractions been around? Care to throw a bone this way? I'll turn it into a tool.