Title:
Function of Recursive Operation in Human Language:
Considering by Evolutionary Simulation of Tool Making

Speaker:
Genta Toya
Japan Advanced Institute of Science and Technology

Abstract:
Human language has hierarchical structures to associate meanings and forms. Theoretical linguists suppose that the minimal operation to make the hierarchical structure is a recursive operation to combine two lexical items into a set. There is a hypothesis that the recursive operation of language evolved from the ability of recursive operation for object manipulation. To clarify the plausibility of this hypothesis, we examine the adaptive function of recursive operation contributing to survival and reproduction using an evolutionary simulation of object manipulation, which is suggested to evolve before language. As a result, it was found that recursive operation had two functions: the diversification of making method and that of products.

In this presentation, we argue that which two typical linguistic activities, communication and thinking, can cause recursive operation. In communication, the recursive operation can produce multiple hierarchical structures for one expression (form). Realizing one expression by multiple hierarchical structures may cause a disadvantage in an environment where speaker and hearer are required to communicate the meaning of message correctly. The recursive operation can also generate new expressions more easily using a part of known expressions. It is adaptive when the diversity of expression is favored in sexual selection. In thinking, such as planning, recursive operation enables people to produce the multiple action sequence for one aim. Multiple action sequence is favorable in an environment where the robustness of planning is adaptive. The recursive operation also enables people to produce a new action sequence, where action sequences established are utilized as its part. This way of planning has the advantage that larger number of action sequences can be composed than non-recursive operation. In sum, planning using recursive operation contributes two ways for adaptation, while communication using it has one adaptive value. Therefore, we conclude that a plausible adaptability of recursive operation is planning.