By demonstrating that variation patterns in ape tool use (e.g., nut-cracking) match cross-linguistic variation patterns in grammatical marking (e.g., mutuality rendition), this study offers novel evidence for the cultural hypothesis of language. Thus the linguistic concept of language as tool receives obvious signs of cultural development seperately from language, and further a model of cognition and learning from primate studies which hitherto has been trivialized in research on language.