It puts forward a new hypothesis concerning language development (inspired by recent ideas in biology) - a punctuated equilibrium model. It is suggested that over most of the 100,000 years or more that languages have been spoken, there has existed a state of equilibrium. Within a given region a number of languages (each spoken by a smallish population) would have existed in a state of relative harmony, with no one language having much greater prestige than any other. Linguistic features would have diffused across the languages of the region so that they gradually converged on a common structural prototype.

The state of equilibrium is, from time to time, punctuated. The trigger could be some natural event (e.g. flood or drought), material innovation (the most notable being the evolution of agriculture), the emergence of an ambitious leader or an aggressive religion, or just geographical movement into new territory. During a period of punctuation we get expansion and split of peoples and of languages. It is then that the family tree model is appropriate - a single proto-language develops into a series of distinct daughter languages, all gradually diverging more and more from the proto-language. The period of punctuation (which will be relatively short, at most just a few thousand years) will gradually merge into a new period of equilibrium (which will be relatively long, often tens or thousands of years).

This explains why it has not been possible to scientifically establish any higher-level links between accepted language families; they probably had their origins in the end of a period of equilibrium. (It is not likely that a 'family-tree-type' period of punctuation would have been immediately preceded by earlier 'family-tree-type' period of punctuation.) The lecture pays particular attention to the criteria for proving genetic relationships between languages, and provides a critique of unscientific work, such as that on lexicostatistics and 'Nostratic'. There is consideration of the nature of putative proto-languages, with the suggestion that some language families may have developed from a group of two or three typologically similar languages (spoken in a small area), rather than from a single language. It is also shown how it may sometimes be impossible to tell whether a particular similarity between languages is evidence for genetic relationship or the result of diffusion.

The final sections consider recent history, and make projections about the future. The expansion of Europeans into every other part of the world - which essentially began in 1492 - has punctuated the linguistic equilibrium that existed in Australia, parts of the Americas and Africa, and so on. A large intrusive culture, with a prestige language that is used almost exclusively in schooling and the media, signals the gradual abandonment of local languages.

In every part of the world the smaller, non-prestige languages are steadily falling towards extinction. The rate of language loss in a community can be slowed, but never halted or reversed. I predict that the only languages which have any chance of survival, in the medium term, are those that are the official language of a nation. And even that will not be the end. With increasing globalisation the end product will be a single language, spoken by everyone.