Language variation/change & community size
I'd always thought that language change should be slower in a smaller community; I think part of the reason that I held so tenaciously onto this belief for so long was due to (1) stories (myths, in some cases) about, for example, how isolated communities speak like their 16th century ancestors, (2) not separating out from these stories other variables such as trade and contact with the outside world and hence other dialects and languages.
Most of all, though, I think my misconception boils down to the difference between variation and change: a small community might not have very much in the way of variation between its speakers, but a single change can travel through the whole population a lot faster and become a part of the language than such a change in a larger community.
I suppose part of the difficulty is teasing out the difference between "language" as a product of the community and "language" as a product of one's own internal grammar. Language change is mostly a property of the first, while variation - how much one's own internal grammar varies from that of the community - is mostly a property of the second.
In the course of thinking about this I came across a few interesting papers, for example "Is the rate of linguistic change constant?" by Daniel Nettle and this simulation of language change, which you may want to check out.
In a moment I'll post about a couple of vaguely linguistically-related pieces I came across today. So the linguistics drought is over.