Structuring unleashed expression: developmental foundations of human communication Wiktor Rorot*, Katarzyna Skowrońska, Ewa Nagórska, Konrad Zieliński, Julian Zubek, Joanna Rączaszek-Leonardi** Human Interactivity and Language Lab, Faculty of Psychology, University of Warsaw * w.rorot@uw.edu.pl, ** raczasze@psych.uw.edu.pl; https://hill.psych.uw.edu.pl This paper is a commentary on Heintz C., Scott-Phillips T. (2022). Expression unleashed: The evolutionary & cognitive foundations of human communication. Behavioral and Brain Sciences. https://doi.org/10.1017/S0140525X22000012 ABSTRACT The target article highlights the sources of open-endedness of human communication. However, the authors’ perspective does not account for the structure of particular communication systems. To this end, we extend the authors’ perspective, in the spirit of Evolutionary Extended Synthesis, with a detailed account of the sources of constraints imposed upon expression in the course of child development. MAIN TEXT Heintz and Scott-Phillips strongly argue that the cognitive capacities required for unleashed communication are adaptations to a ‘partner choice’ social ecology. This emphasis on adaptation and ecology puts them roughly within the purview of modern evolutionary synthesis (Huxley 2010). However, arguments against both the adaptationist paradigm and the program of modern synthesis have been accruing systematically for a long time (e.g., Gould and Lewontin 1979; Sober 1982; Walsh and Huneman 2017) and resulted in several alternative proposals, out of which the Extended Evolutionary Synthesis is one of the most prolific (Laland et al. 2015; Pigliucci and Müller 2010). Evolutionary Extended Synthesis positions at its center the study of development (developmental bias and plasticity) and niche construction. These are precisely the elements that we argue that the authors overlooked in their proposal, and which can provide important details not only about how expression becomes ‘unleashed,’ but also how it can become highly structured to enable the emergence of symbolic communication systems, such as language. The target article draws the continuity between different forms of human expression, moving the search for foundations of the unleashed communication, i.e., the generativity of communication