This project relates variability in heritage languages to diachronic processes of language change. We test the hypothesis that attested pathways of language change can predict the processing profiles of native speakers. To test this, we conduct experiments on two phenomena from the domain object realization: clitic doubling in Spanish and null objects in Portuguese. We compare heritage speakers of the European varieties of Spanish and Portuguese with speakers of Latin American varieties that are assumed to be more advanced diachronically with regard to the corresponding phenomena: Rioplatense Spanish and Brazilian Portuguese. Our results will contribute to a better understanding of the language competence of native speakers of Spanish and Portuguese and, at the same time, to research on diachronic and dialectal variation in Spanish and Portuguese.