I came across this interesting passage in Michael Cook's A Brief History of the Human Race. He is using the Mesoamerican calendars to simultaneously illustrate both the underlying tendency of people towards diversity and at the same time the shared nature of their humanity.
This family of calendars provides a good example of a phenomenon widespread in human cultures. Few societies can do without a calendar of some kind, and a complex society needs a reasonably precise one. Once it posesses such a calendar, it may have to adjust it from time to time, but there is no need to embroider it. Our own claendar is a case in point: it works, and for the most part that is enough for us. But cultures have a way of picking on some aspect or other of their pragmatic arrangements, and elaborating them in respects that have no obvious utilitarian justification. This seems to be the case with Australian subsections; it is undoubtedly so with Mesoamerican calendars. What we see here is again a human propensity for gratuitous cultural embroidery. The reason the example is a good one is simply its dramatic visibility to anyone coming from a Western culture: it so happens that our restraint in calendric matters contrasts sharply with the extravagance of the Mesoamericans.
Yet these same calendars can also be used to illustrate the limits of cultural diversity among humans. A Mesoamerican calendar is immediately recognizeable for what it is - a calendar, not some exotic practice bearing only a faint resemblance to what in our culture is called a calendar. Moreover, it is quite obviously a calendar developed by people living on the same planet as ourselves: it takes the day for granted as the basic calendric unit and constructs a year of 365 days. Where we have trouble grasping the workings of these calendars, the reason is merely that they are intricate and unfamiliar; they are far from being so deeply alien to us that we do ot know how to begin to understand them.