Croft 2003 argues that "the typological universals discovered in contemporary languages should also apply to ancient and reconstructed languages" (the so called uniformitarian hypothesis, p. 233). How so? I don't quite follow his logic. How do new features emerge then? I'd appreciate some references.
Update: Let me borrow an example from Burlak and Starostin 2005. Let's say, we have three daughter languages, X, Y, and Z. Some feature F is present in all of those languages but it is realized by different means, F(x), F(y), and F(z). F(x) is the most typologically frequent form (based on "global" typology, not necessarily in this taxon), whereas F(y) and F(z) are less frequent. Now we need to reconstruct that feature for the parent language, W. What should we choose? Synchronic typologists would argue that it should be the most frequent form, F(x) in our case. Now there's the problem. If the parent language W indeed had the most frequent form F(x), then we'd have to argue that language states can change from a more typologically probable state to a less typologically probable one, a very undesirable result.