Languages are often compared to living species because of the way in which they diverge into new tongues over time in an ever-growing linguistic tree. Some critics have claimed that this comparison is a superficial one, a nice metaphor but nothing more.
But the new study by Quentin Atkinson, now at the University of Oxford, suggests that languages evolve at a similar stop-and-start pace, which uncannily echoes a long-standing theory in biology, known as ‘punctuated equilibrium’. The theory’s followers claim that life on Earth also evolved at an uneven pace, full of rapid bursts and slow periods.
Famously championed by the late Stephen Jay Gould, the punctuated equilibrium theory suggests that most species change very little over time and big evolutionary changes are concentrated at rare moments where new species branch off from existing lineages. Together with colleagues from the US and New Zealand, Atkinson found similar patterns in three of the worlds’ largest families of languages.
They compared lists of words from the Indo-European group, which include English and Hindi; the Bantu group, consisting of several hundred African languages; and the Austronesian group, which includes over a thousand tongues from Indonesia, Papua New Guinea and the Polynesian islands. Between them, these three families account for a third of all the world’s languages.
Of course, languages borrow words from each other all the time and indeed, 50% of English words are loans from French and Latin. That was a potential pitfall of the study and Atkinson avoided it by only considering basic words such as numerals, body parts and pronouns that are very unlikely to have been co-opted from another tongue.
For each group, Atkinson built a family tree showing how newer languages split off from ancestral ones. The trees mirrored those that biologists use to chart the evolutionary relationships between species.
In the model, the birth of new languages is represented by new branches on the tree and the length of each branch depends on the difference in vocabulary between the new tongue and its parent one. The greater the changes, the longer the branch.
In each family tree, Atkinson saw that the parts of the tree with the most branches also had the longest ones. So groups that spawned the highest number of new languages also diverged most significantly in their repertoire of words. That’s the pattern you would expect if the birth of new languages triggered bursts of rapid evolution. If the pace of evolution was more constant, the number of branch points would have no effect on overall branch length.
The need for speed
These rapid bursts accounted for 31% of the vocabulary differences between Bantu speakers, 21% of the differences in Indo-European languages and 10% of the variation in the Austronesian group. For comparison, team estimated that these fast and slow evolutionary cycles explained about 22% of the genetic differences between biological species.
As they split from each other, new sister tongues begin to adopt new words at a fast pace and these are probably accompanied by equally quick changes in pronunciation, spelling and grammar. As their identities become clearer, the pace of change slows.
Atkinson thinks that this process happens when different groups of people try to establish distinct social identities by exaggerating differences in language. American English may have developed along these lines and the need for a unique identity was at the forefront of Noah Webster‘s mind when he published his first American Dictionary of the English Language in 1828. “As an independent nation, our honour requires us to have a system of our own, in language as well as government,” he said.
For more on the evolution of language, have a look at this post on the evolution of the past tense in English verbs.