This programmatic article describes how the two types of cross-cultural research (comparative ethnography and comparative archaeology) can provide a Rosetta stone to help us discover the original homelands of protolanguage groups. Here, the focus is on Proto-Afroasiatic and Proto-Indo-European. If words reconstructed by historical linguists for a protolanguage reflect cultural and environmental features, and if those features have material or archaeological indicators (which we can discover by the two types of cross-cultural research), then the archaeological record can be searched for sites that have the expected combinations of features. The likely homeland of the protolanguage should be the site or local region that has significantly more of those indicator features than other sites or local regions.