Current analyses present lexical borrowing as a pervasive phenomenon in pre-colonial Australia. They propose that this follows from the high levels of multilingualism and language group exogamy which characterized pre-colonial sociality. This article shows that lexical borrowing was not pervasive in Australia, arguing that there is no necessary or even default relation between high levels of multilingualism and language group exogamy, and high levels of borrowing. These social phenomena may equally be accompanied by extremes of lexical differentiation between languages. Australia provides many examples of such differentiation. The paper also argues that there are no examples of the borrowing of lexical material from irregular paradigms in Australia. As such, the sharing of lexical material from irregular paradigms is a reliable guide to genetic relations in Australia.