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By Jason Palmer Science and technology reporter, BBC News
Language brain centres during MRI The study challenges the idea that the
"language centres" of our brains are the sole driver of language
A 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 trees
Modern 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.
Pea plants in a greenhouse The methods use inference in a similar way to
Mendel's studies of pea plants
The models revealed that while different language structures in the family tree
could be seen to evolve along the branches, just how and when they evolved
depended on which branch they were on.
"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."