The existence of complex structures involved in cultural skills is one of the unique characteristics in humans. Since human language is also complexly structured, we can presume that the ability to merge and divide units (structuration ability) contributes to their existence. To investigate the emergence of structuration ability archeologically, we must confirm its effect on cultural evolution. Using mathematical models, we study whether structuration ability leads to an increase in the difficulty of the cultural skills that can be maintained in the population. We show that even if individuals have structuration ability, the maximum difficulty of a maintainable cultural skill is unchanged provided that the individuals must learn every component skill step by step to master the structured skill; however, if individuals can learn each component skill in parallel, the maximum difficulty might increase. When the cultural skill affects the mortality or injury rate of its carriers, the structuration ability inhibits cultural evolution under some conditions. These results indicate the importance of the learning process and the role of structured cultural skills on cultural evolution.
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