Q. I never understood the area of ethnomathematics. I hear about it a lot but fail to see how mathematical truths are shaped by culture.
R. Mathematical truths in one sense are universal. They are not dependent on culture - the formula for the area of a triangle would be the same in all human cultures, and perhaps in all possible universes where these concepts - area, triangle, formula - occur in our familiar sense. But consider that mathematics, along with language and music, artistic expression, moral reasoning and religious experience and reflection, are all uniquely human capacities that occur to a greater or lesser extent in all human societies and individuals, and permit an infinite variety of expressions in all cultures - but in ways that reflect local histories and cultures. In this sense the formula for the area of a plane triangle is as much of a product of an age and culture as zero, or the musical form known as the fugue, or cubism or creole or christianity. Contemporary mathematicians may not be able to conceive of mathematics, or indeed a world, without the logarithm or computer programs (all mathematical entities that are universal in a certain sense), but they did exist.
If we regard mathematics as a set of truths, then once discovered or invented, they are universal in the sense that they command universal assent among people who have the training and experience to understand what's going on. (That they are universal in the sense that they are necessary truths in all possible universes, I do not claim for now, because I don't know for sure.) If we regard mathematics as a set of methods of investigating the world, or as a set of social practices (as opposed to a body of truths), then I would have to say that mathematics is very much dependent on culture. In this sense, ethnomathematics makes as much sense as ethnomusicology or anthropology.