By Jason PalmerScience and technology reporter, BBC News
Thestudy challenges th idea that the "language centres" of our brains are the sole driver of languageA long-standing idea that human languages share universal features that are dictated by human brain structure has been cast into doubt.
A study
reported in Nature has borrowed methods from evolutionary biology to trace the development of grammar in several language families.
The results suggest that features shared across language families evolved independently in each lineage.
The authors say cultural evolution, not the brain, drives language development.
At the heart of both studies is a method based on what are known as phylogenetic studies.
Lead author Michael Dunn, an evolutionary linguist at the Max Planck Institute for Psycholinguistics in the Netherlands, said the approach is akin to the study of pea plants by Gregor Mendel, which ultimately led to the idea of heritability of traits.
"By looking at variation amongst the descendant plants and knowing how they were related to each other, [Mendel] could work out the mechanisms that must govern that variation," Dr Dunn explained to BBC News.
"He inferred the existence of some kind of information transfer just from knowing family trees and observing variation, and that's exactly the same thing we're doing."
Family treesModern phylogenetics studies look at variations in animals that are known to be related, and from those can work out when specific structures evolved.
For their studies, the team studied the characteristics of word order in four language families: Indo-European, Uto-Aztec, Bantu and Austronesian.
They considered whether what we call prepositions occur before or after a noun ("in the boat" versus "the boat in") and how the word order of subject and object work out in either case ("I put the dog in the boat" versus "I the dog put the canoe in").
The method starts by making use of well-established linguistic data on words and grammar within these language families, and building "family trees" of those languages.
"Once we have those trees we look at distribution of these different word order features over the descendant languages, and build evolutionary models for what's most likely to produce the diversity that we observe in the world," Dr Dunn said.
The methods use inference in a similar way to Mendel's studies of pea plantsThe results showed that, although grammatical features were shared across the families, the way that the features arose depended strongly on the history of development of language features within the families.
In a parallel to convergent evolution in biology - in which analogous structures in unrelated animals can evolve independently - grammatical constructs follow their own independent evolutionary paths.
"We show that each of these language families evolves according to its own set of rules, not according to a universal set of rules," Dr Dunn explained.
"That is inconsistent with the dominant 'universality theories' of grammar; it suggests rather that language is part of not a specialised module distinct from the rest of cognition, but more part of broad human cognitive skills."
The paper asserts instead that "cultural evolution is the primary factor that determines linguistic structure, with the current state of a linguistic system shaping and constraining future states".
However, co-author and evolutionary biologist Russell Gray of the University of Auckland stressed that the team was not pitting biology against culture in a mutually exclusive way.
"We're not saying that biology is irrelevant - of course it's not," Professor Gray told BBC News.
"But the clumsy argument about an innate structure of the human mind imposing these kind of 'universals' that we've seen in cognitive science for such a long time just isn't tenable."
Steven Pinker, a cognitive scientist at Harvard University, called the work "an important and welcome study".
However, Professor Pinker told BBC News that the finer details of the method need bearing out in order to more fully support their hypothesis that cultural boundaries drive the development of language more than biological limitations do.
"The [authors] suggest that the human mind has a tendency to generalise orderings across phrases of different types, which would not occur if the mind generated every phrase type with a unique and isolated rule.
"The tendency may be partial, and it may be elaborated in different ways in differently language families, but it needs an explanation in terms of the working of the mind of language speakers."
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