From Nature:
Languages show periodic bursts of evolution, in which many new words blossom, according to new research that treats linguistic evolution like its biological counterpart. The research suggests that new words evolve slowly most of the time, but with spurts of diversification when two languages divide.
If all language evolved at the same stately pace, the distance between any two languages could be easily calculated by multiplying this constant by how long ago the two tongues parted ways. But in this week’s Science, Mark Pagel, an evolutionary biologist at the University of Reading, UK, and his colleagues have found that branches heavy with linguistic divorces evolve faster, suggesting ‘punctuational bursts’ of language change when two languages split.
The authors calculate that the rapid change in these bursts accounts for between 10% and 33% of total word differences between languages.
More here.