What makes us smart? Human body cells function in the same way as those of animals, and even the core cognitive competencies for vision, quantity perception, object mechanics, and other domains are virtually the same in humans as in some animals. Nevertheless humans have addressed the basic problems of life (food, shelter, mating, locomotion, etc.) in completely different ways from even their closest animal kin, and have risen to dominate the planet. Recently complex syntactic processing has been identified as one core area where humans differ from primates. The central question of the CHLaSC project is: How much of human uniqueness can be traced back to this one basic difference? Addressing this question is a team from five different fields (biology, semantics, language acquisition, cognitive development, and anthropology). We focus on structural complexity in language and in other cognitive systems, and the question whether extra-linguistic structural complexity is derived from language. The three core objectives we pursue are: 1) Describe precisely the difference in syntactic processing ability from a comparative, developmental, and socio-cultural perspective. 2) Develop formal models of the semantic mechanisms relating language to other cognitive domains. 3) Investigate how variation in the use of structural complexity in language correlates with the availability of structural complexity in social cognition. This project complements the already funded Neurocom project in the behavioural and socio-cultural domain. The CHLaSC project integrates linguistic semantics with the cognitive sciences, which is expected to broadly impact both fields and open up many new research opportunities. A broader social impact arises from the work on cognitive disorders, where opportunities for applications in diagnosis, therapy, and genetic research arise.