i don't think that the rate of change is differentSome linguists hold that the rate of language change is constant and can be measured: most famously Morris Swadesh and his
glottochronology. (A modern proponent is
Don Ringe of UPenn who uses computational model based on cladistics in biology to determine when languages split off into separate branches: some papers
here.) Others reason that the rate is variable. R M W Dixon, an Australian linguist, wrote an interesting, short book,
The Rise and Fall of Languages (1997), in which he posits a model for language change that replaces the familiar
Stammbaumtheorie (family tree theory of Johann Schmidt) of languages genetic relationship with one borrowed from from evolutionary biology, i.e.,
punctuated equilibrium. (It is, in part, based on some ideas from
areal linguistics, e.g., the concept of the
Sprachbund.)
It can be observed that the change between Old and Modern English and between Vulgar Latin and the various Romance languages took place fairly rapidly during the so-called Dark Ages, a volutile period when little in the way of literature was written or survived.
