Ius Filiationis: A defence of Citizenship by Descent 85 American states.3 Only those born in the territory are considered nationals (they are sometimes also called ‘naturals’). They turn into citizens with full voting rights at the age of majority. Immigrants who naturalise become citizens, but not nationals. They remain excluded from many public offices (also the US president still has to be a ‘natural born citizen’) and they can be deprived of their citizenship status, whereas nationality can often never be lost. In Uruguay even the concept of ‘naturalisation’ does not exist because those who are not born in the territory can never become ‘naturals’. Similar exclusionary effects of ius soli traditions apply to those born abroad to citizen parents. They often do not acquire citizenship unless they are registered in time by their parents and they may lose it unless they ‘return’ before the age of majority. If both ius sanguinis and ius soli are tainted in these ways, should we consider an even more radical alternative of abandoning citizenship by birth altogether? Why not replace it with ius domicilii so that citizenship is acquired automatically with taking up residence and lost with outmigration? Or should we maybe replace it with ius pecuniae,4 i.e. a global market for citizenships in which individuals can bid for membership status anywhere and states can set the admission price? Neither of these alternatives is morally attractive and something important is lost when we give up birthright citizenship. Why not ius filiationis? Dumbrava’s second argument is that developments in reproduction technologies and in the social and legal recognition of new family patterns make ius sanguinis increasingly unworkable and obsolete. This problem is not entirely new and a solution is already available. International law has long abandoned the idea that children should acquire only one citizenship at birth. Since they can inherit two different ­citizenships from the mother’s and the father’s side (maybe in addition to a third one acquired iure soli), why should they not receive the citizenship of both an 3 4 Acosta D, (2016), ‘Regional Report on Citizenship: The South American and Mexican Cases’, EUDO Citizenship Observatory Comparative Reports 2016/01, Florence: European University Institute, available at http://cadmus. eui.eu//handle/1814/43325 Stern, J. (2011), ‘Ius Pecuniae – Staatsbürgerschaft zwischen ausreichendem Lebensunterhalt, Mindestsicherung und Menschenwürde’, Migration und Integration – wissenschaftliche Perspektiven aus Österreich, Jahrbuch 1/2011, Dahlvik/Fassmann/Sievers (eds.). See also Part I of this volume; Dzankic, J. (2015), ‘Investment-based citizenship and residence programmes in the EU’, Robert Schuman Centre for Advanced Studies Working Papers 2015/08, Florence: European University Insitute.