Psychologists from The University of Auckland have just published two major studies on the diversity of the world's languages in the journals Science and Nature.
The first study, published in Science by Dr Quentin Atkinson, provides strong evidence for Africa as the birthplace of human language.
An analysis of languages from around the world suggests that, like our genes, human speech originated -- just once -- in sub-Saharan Africa. Atkinson studied the phonemes, or the perceptually distinct units of sound that differentiate words, used in 504 human languages today and found that the number of phonemes is highest in Africa and decreases with increasing distance from Africa.
The fewest phonemes are found in South America and on tropical islands in the Pacific Ocean. This pattern fits a "serial founder effect" model in which small populations on the edge of an expansion progressively lose diversity. Dr Atkinson notes that this pattern of phoneme usage around the world mirrors the pattern of human genetic diversity, which also declined as humans expanded their range from Africa to colonise other regions.
In general, the areas of the globe that were most recently colonised incorporate fewer phonemes into the local languages whereas the areas that have hosted modern humans for millennia (particularly sub-Saharan Africa) still use the most phonemes.
This decline in phoneme usage cannot be explained by demographic shifts or other local factors, and it provides strong evidence for an African origin of modern human languages -- as well as parallel mechanisms that slowly shaped both genetic and linguistic diversity among humans.
The second study, published in Nature by University of Auckland researchers Professor Russell Gray and Dr Simon Greenhill and their colleagues Michael Dunn and Stephen Levinson at the Max Planck Institute for Psycholinguistics in the Netherlands challenges the idea that the human brain produces universal rules for language.
"The diversity of the world's language is amazing," says Professor Gray. "There are about 7,000 languages spoken today, some with just a dozen contrastive sounds, others with more than 100, some with complex patterns of word formation, others with simple words only, some with the verb at the beginning of the sentence, some in the middle, and some at the end."
"Our work shows that the claims some linguists have made for a really strong role of the innate structure of the human mind in shaping linguistic variation have been hugely oversold," he says.
Using computational methods derived from evolutionary biology, Gray and his team analysed the global patterns of word-order evolution. Instead of universal patterns of dependencies in word-order features, they found that each language family had its own evolutionary tendencies.
"When it comes to language evolution, culture trumps cognition," Gray observes.
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