Modeling Coevolution between Language and Memory Capacity during Language Origin

<div><p>Memory is essential to many cognitive tasks including language. Apart from empirical studies of memory effects on language acquisition and use, there lack sufficient evolutionary explorations on whether a high level of memory capacity is prerequisite for language and whether language origin could influence memory capacity. In line with evolutionary theories that natural selection refined language-related cognitive abilities, we advocated a coevolution scenario between language and memory capacity, which incorporated the genetic transmission of individual memory capacity, cultural transmission of idiolects, and natural and cultural selections on individual reproduction and language teaching. To illustrate the coevolution dynamics, we adopted a multi-agent computational model simulating the emergence of lexical items and simple syntax through iterated communications. Simulations showed that: along with the origin of a communal language, an initially-low memory capacity for acquired linguistic knowledge was boosted; and such coherent increase in linguistic understandability and memory capacities reflected a language-memory coevolution; and such coevolution stopped till memory capacities became sufficient for language communications. Statistical analyses revealed that the coevolution was realized mainly by natural selection based on individual communicative success in cultural transmissions. This work elaborated the biology-culture parallelism of language evolution, demonstrated the driving force of culturally-constituted factors for natural selection of individual cognitive abilities, and suggested that the degree difference in language-related cognitive abilities between humans and nonhuman animals could result from a coevolution with language.</p></div

Marginal mean <i>UR</i> (a) and LTM capacity (b) in the sets with and without natural (<i>Nat</i>) or cultural (<i>Cul</i>) selection.

<p>Mean <i>UR</i> and LTM capacity throughout 2000 generations in the sets with natural selection (c) and without (d). Error bars denote standard errors. Initial LTM capacity is 30.</p

Mean <i>UR</i> and LTM capacity throughout 5000 generations in the sets with natural selection (a) and without (b).

<p>Initial LTM capacity is 20.</p

Examples of acquisition of syntactic categories and syntactic rules.

<p>M-U mappings are itemized by Arabic numbers, and lexical rules by Roman numbers.</p

Examples of lexical rules, syntactic rules, and categories.

<p>“#” denotes unspecified constituents, and “*” unspecified syllable(s). S, V, and O are syntactic roles of categories. Numbers in () denote rule strengths, and those in [] association weights. “<<” denotes the local order <i>before</i>, and “>>” <i>after</i>. Compositional rules can combine, if specifying each constituent in an integrated meaning exactly once, e.g., rules (c) and (d) can combine to encode “chase〈wolf, bear〉” with /ehfg/. Lexical and syntactic knowledge collectively encode integrated meanings, e.g., to express “fight〈wolf, fox〉” using the lexical rules in the S, V, and O categories and the syntactic rules SV and SO, the resulting sentence is /bcea/ or /bcae/, following SVO or SOV.</p

Parameter setting of the simulations.

<p>Parameter setting of the simulations.</p

Mean peak-<i>UR</i> (the highest <i>UR</i> throughout all generations) (a)(c) and <i>Gen</i> (b)(d) in the <i>NoChange</i> set of simulations.

<p>Error bars denote standard errors.</p

Theoretical framework (adapted from [41]).

<p>Theoretical framework (adapted from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0142281#pone.0142281.ref041" target="_blank">41</a>]).</p

Parameter setting for the learning mechanisms and communication scenario.

<p>Parameter setting for the learning mechanisms and communication scenario.</p

Example sentences showing the blocking effect on <i>ziji</i>.

<p>Sentence (1) has one occurrence of <i>ziji</i>. Sentence (2) has two occurrences of <i>ziji</i> (from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073226#pone.0073226-Huang5" target="_blank">[16]</a>, pp. 340 (36)). Sentences (3) and (4) show the exceptions to such blocking effect (from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0073226#pone.0073226-Xu1" target="_blank">[2]</a>). For each sentence, the first line shows the Roman spelling of this sentence, the second line shows the word gloss, and the third line shows the English translation. (a)–(g) are possible interpretations of the two <i>ziji</i>s in sentence (2). (h) and (i) are unacceptable ones, thus marked by “*”.</p