Last week I sat in on a class of teachers and the topic of the evenness or oddness of zero came up. The primary stances taken by the participants were essentially it was even or neither. Interested, I checked out a few mathematical sources and found there was support for both views: if one defines evenness or oddness on the integers (either positive or all), then zero seems to be taken to be even; and if one only defines evenness and oddness on the natural numbers, then zero seems to be neither.
My impression is that conceptually even and oddness (in a few variations) substantially predated zero and the negative integers. So my question is: it known when and how evenness and oddness were extended from the natural numbers to the integers? There seems to have been substantial dislike of the negative integers (one source mentions into the 1800s) so an early extension might have been to the positive integers (although zero being even seems most useful if the negative integers are included).