Abstract
In this paper, we revisit a mathematical model of sign language persistence by Aoki and Feldman (Theor Popul Biol 39(3):358–372, 1991), which investigates the evolution of genes causing deafness, affected by an assortative mating parameter, and the cultural transmission of sign language. To assess their model, we reimplement it as an agent-based simulation to be able to easily represent structured relationships in a finite population. We study the persistence of shared sign languages, a categorization of sign languages, which are typically shared by deaf and hearing members of a small community with a high incidence of hereditary deafness (Nyst, 2012. Shared sign languages. Sign language: An international handbook, pp. 552–574). We observe how shared sign language persistence is affected by hearing signers, marriage patterns, and various modes of sign language transmission: vertical, horizontal, oblique, and grandparental transmission. In contrast to Aoki and Feldman’s (Theor Popul Biol 9(3):358–372, 1991) finding that modes of transmission other than vertical are negligible, in the agent-based model we find that adding modes of transmission helps to ensure shared sign language persistence. A better understanding of sign language persistence has relevance for processes of cultural evolution, (sign language) linguistics, and language endangerment.
Highlights
Human evolution has been shaped by interactions between genes and culture (Aoki and Feldman, 1991)
We focus on various modes of sign language transmission, and on the effect of marriage patterns and hearing signers on sign language persistence
We investigate eight different cases: vertical transmission alone (V), vertical and horizontal transmission (VH), vertical and oblique transmission (VO), vertical and grandparental transmission (VG), vertical, horizontal and oblique transmission (VHO), vertical, horizontal and grandparental transmission (VHG), vertical, oblique and grandparental transmission (VOG), and vertical, horizontal, oblique and grandparental (VHOG)
Summary
Human evolution has been shaped by interactions between genes and culture (Aoki and Feldman, 1991). The theory of gene–culture coevolution posits that genes and culture are interacting systems, in which offspring inherit both genetic and cultural material (Feldman and Cavalli-Sforza, 1976). Models of gene–culture coevolution typically find faster rates of change than models from conventional population genetics (Feldman and Laland, 1996). It has been estimated that up to 10% of the human genome may be influenced by positive selection (Williamson et al, 2007), a few examples being lactase persistence (Holden and Mace, 2009; Bersaglieri et al, 2004), handedness (Laland et al, 1995) and the evolution of language-facilitating genes like FOXP2 (Coop et al, 2008). It is difficult to thoroughly examine many of these cases; the phenotype and cultural conditions favoring a given phenotype are no longer available for examination, as these changes have taken place at various points in the course of human evolution
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