Luke McCrohon suggests that tools from evolutionary biology can be applied to linguistic borrowing between languages. McCrohon correctly points out that the descent of lexicons are far from tree-like, and there is a great deal of horizontal transfer (see also my post on analysing an etymology dictionary). Although it's mainly nouns that are borrowed into a language, any feature can potentially be borrowed, according to Thmason & Kaufman (1988). However, we tend to observe hierarchies of borrowing such that some types of words are borrowed more frequently than others. For instance, Haugen notes that nouns are more likely to be borrowed than verbs, which are in turn more likely to be borrowed than prepositions. McCrohon links this with a similar observation in biological evolution that certain types of genes are more likely to be borrowed. Informational genes (that provide the basis for functions) are less likely to be borrowed than operational genes (that modify other functions). Jain et al.'s (1999) complexity hypothesis suggests that, while all genes have the same probability of being copied, simpler genes are more likely to be copied faithfully since they have fewer constraints on the precise form they must take to be effective.
McCrohon argues that In a similar way, the explanation of the linguistic borrowing hierarchy might also reflect the increasing constraints on how a word can be used. For instance, most nouns can be substituted by other nouns, while prepositions are highly restricted by context or domain. Also, language-interal change might be affected by these restrictions. Even if there is a more effective form than in the existing system, removing one form might have knock-on consequences for the whole system. This inter-connectedness could have implications for how languages are likely to change.
Furthermore, this model might predict that words are equally likely to be selected for borrowing, but only certain types have a good likelihood of being successfully borrowed. However, a commenter wondered about words that are borrowed to fill conceptual gaps such as new technologies. Still, an interesting analogy between problems in biology and problems in linguistics. And McCrohon is confident that his studies will also have something to give back to the biology community by studying how this problem applies to linguistics.