The project seeks to develop a new theoretical framework to understand the nature and limits of language variation, and test it empirically. The framework reflects recent theoretical changes, as well as empirical findings that cast doubt on the standard account of language variation known as the ‘principles and parameters’ framework. Inspired by the Evo-Devo (evolutionary-developmental) program in biology, which seeks to unveil how developmental processes become modified during evolution and how from these changes the past and present biodiversity arose, I set out to investigate the nature of linguistic variation by paying attention to the many factors that enter into the design of the human language faculty. I suggest ways to remedy the inadequacies of the Standard model by reducing lexical (morphological) variation to four ingredients (which define the limits of variation) and by stressing the role of learning biases (not necessarily specific to language) to account for cross-linguistic tendencies. The proposed program of research has the potential of not only filling in an important gap in our understanding of the nature of human languages, but also could serve as a bridge between various schools of thoughts in linguistics (formalist, functionalist, nativist, emergentist, etc.), which are all too often seen as competitors. In addition, if the evo-devo parallelism is on the right track, this proposal makes a key contribution to the emerging field of Biolinguistics, which aims at uncovering the biological foundations of the human language faculty