I've been spending a lot of time recently thinking about borrowing and it's impact on language evolution and change. In particular, I've been looking at work by Russel Gray and the like on borrowing in IE. Here's an abstract to one of the articles I've been reading: http://rspb.royalsocietypublishing.org/content/early/2010/11/23/rspb.2010.1917.full Language evolution is traditionally described in terms of family trees with ancestral languages splitting into descendent languages. However, it has long been recognized that language evolution also entails horizontal components, most commonly through lexical borrowing. For example, the English language was heavily influenced by Old Norse and Old French; eight per cent of its basic vocabulary is borrowed. Borrowing is a distinctly non-tree-like process—akin to horizontal gene transfer in genome evolution—that cannot be recovered by phylogenetic trees. Here, we infer the frequency of hidden borrowing among 2346 cognates (etymologically related words) of basic vocabulary distributed across 84 Indo-European languages. The dataset includes 124 (5%) known borrowings. Applying the uniformitarian principle to inventory dynamics in past and present basic vocabularies, we find that 1373 (61%) of the cognates have been affected by borrowing during their history. Our approach correctly identified 117 (94%) known borrowings. Reconstructed phylogenetic networks that capture both vertical and horizontal components of evolutionary history reveal that, on average, eight per cent of the words of basic vocabulary in each Indo-European language were involved in borrowing during evolution. Basic vocabulary is often assumed to be relatively resistant to borrowing. Our results indicate that the impact of borrowing is far more widespread than previously thought. So, I'm curious. In light of this, how many of you work in borrowings from non-native phonologies/lexicons into your conlangs? Is it necessary to set up several different families and related languages in order to have a realistic conlang? What do you guys think about this sort of thing? The age of the language and contact is of course a factor.