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      Cumulative cultural evolution, population structure and the origin of combinatoriality in human language

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          Abstract

          Language is the primary repository and mediator of human collective knowledge. A central question for evolutionary linguistics is the origin of the combinatorial structure of language (sometimes referred to as duality of patterning), one of language’s basic design features. Emerging sign languages provide a promising arena to study the emergence of language properties. Many, but not all such sign languages exhibit combinatoriality, which generates testable hypotheses about its source. We hypothesize that combinatoriality is the inevitable result of learning biases in cultural transmission, and that population structure explains differences across languages. We construct an agent-based model with population turnover. Bayesian learning agents with a prior preference for compressible languages (modelling a pressure for language learnability) communicate in pairs under pressure to reduce ambiguity. We include two transmission conditions: agents learn the language either from the oldest agent or from an agent in the middle of their lifespan. Results suggest that (1) combinatoriality emerges during iterated cultural transmission under concurrent pressures for simplicity and expressivity and (2) population dynamics affect the rate of evolution, which is faster when agents learn from other learners than when they learn from old individuals. This may explain its absence in some emerging sign languages. We discuss the consequences of this finding for cultural evolution, highlighting the interplay of population-level, functional and cognitive factors.

          This article is part of a discussion meeting issue ‘The emergence of collective knowledge and cumulative culture in animals, humans and machines’.

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          Demography and Cultural Evolution: How Adaptive Cultural Processes can Produce Maladaptive Losses: The Tasmanian Case

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            The Neutral Theory of Molecular Evolution

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              Language Structure Is Partly Determined by Social Structure

              Background Languages differ greatly both in their syntactic and morphological systems and in the social environments in which they exist. We challenge the view that language grammars are unrelated to social environments in which they are learned and used. Methodology/Principal Findings We conducted a statistical analysis of >2,000 languages using a combination of demographic sources and the World Atlas of Language Structures— a database of structural language properties. We found strong relationships between linguistic factors related to morphological complexity, and demographic/socio-historical factors such as the number of language users, geographic spread, and degree of language contact. The analyses suggest that languages spoken by large groups have simpler inflectional morphology than languages spoken by smaller groups as measured on a variety of factors such as case systems and complexity of conjugations. Additionally, languages spoken by large groups are much more likely to use lexical strategies in place of inflectional morphology to encode evidentiality, negation, aspect, and possession. Our findings indicate that just as biological organisms are shaped by ecological niches, language structures appear to adapt to the environment (niche) in which they are being learned and used. As adults learn a language, features that are difficult for them to acquire, are less likely to be passed on to subsequent learners. Languages used for communication in large groups that include adult learners appear to have been subjected to such selection. Conversely, the morphological complexity common to languages used in small groups increases redundancy which may facilitate language learning by infants. Conclusions/Significance We hypothesize that language structures are subjected to different evolutionary pressures in different social environments. Just as biological organisms are shaped by ecological niches, language structures appear to adapt to the environment (niche) in which they are being learned and used. The proposed Linguistic Niche Hypothesis has implications for answering the broad question of why languages differ in the way they do and makes empirical predictions regarding language acquisition capacities of children versus adults.
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                Author and article information

                Contributors
                Journal
                Philos Trans R Soc Lond B Biol Sci
                Philos Trans R Soc Lond B Biol Sci
                RSTB
                royptb
                Philosophical Transactions of the Royal Society B: Biological Sciences
                The Royal Society
                0962-8436
                1471-2970
                January 31, 2022
                December 13, 2021
                December 13, 2021
                : 377
                : 1843 , Discussion meeting issue ‘The emergence of collective knowledge and cumulative culture in animals, humans and machines’ organized and edited by Andrew Whiten, Dora Biro, Ellen C. Garland and Simon Kirby
                : 20200319
                Affiliations
                [ 1 ] Centre for Language Evolution, University of Edinburgh, , Edinburgh, UK
                [ 2 ] Department of Psychology, Heriot-Watt University, , Edinburgh, UK
                Author notes
                Author information
                http://orcid.org/0000-0003-4688-1774
                Article
                rstb20200319
                10.1098/rstb.2020.0319
                8666903
                34894728
                ec96cf0f-572c-4462-a371-ac45ee6800c6
                © 2021 The Authors.

                Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                History
                : July 2, 2021
                : July 2, 2021
                Categories
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                Research Articles
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                January 31, 2022

                Philosophy of science
                combinatoriality,population dynamics,cultural evolution of language
                Philosophy of science
                combinatoriality, population dynamics, cultural evolution of language

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