Please read Part I, Part II, and Part III before reading this post.

I would like to end this series of posts on glottochronology with some exercises, taken from Sandefur’s book Discrete Dynamical Systems (Oxford, 1990).

1. Two groups of people have a common language. From a list of 250 words, the two groups have 220 in common. How long ago did these two groups split from one?

2. Consider the model of glottochronology. Assume a language is given today.

(a) How long will it take for 1/4 of the words to change?

(b) How long will it take for 10 per cent of the words to change?

3. Suppose that person A knows 60 per cent of a list of 1000 words, person B knows 70 per cent of that list, and person C knows 30 per cent of that list.

(a) How many words do you expect all three people know?

(b) What per cent of the words is known by A and B but not by C?


Problems 1 and 2 are solved with the equations provided in the previous posts. Problem 3 is solved by applying the multiplication principle  to A, B, and C.