The little that was on NPR said that they spanned a few centuries. I know that some gross structures vary quite widely based on environment (that difference between round and long skulls that so many phrenologist and Social Darwinists used to castigate what whipping boys they would? Diet based. Long skulls (which are a neoteny trait iirc) happen in progeny that get increased diet to their round skulled paren†s. (semi-explaining why 'corn-fed farm boys' are a distinct body type*))

*as in all things human, there is variation within a group at least as significant as similarity between groups.