To tackle global challenges like climate change or pandemics, large-scale cooperation is needed. Cooperation and its maintenance are traditionally seen as a conflict between pro-sociality (dedicating resources towards public goods) and free-riding (taking advantage of the cooperation of others). Yet, when faced with shared problems that require cooperation, individuals may also have the ability to solve them individually. Societies often, and increasingly so, provide individuals with means to become independent of public goods through, e.g., private healthcare or retirement planning. How such opportunities of self-reliance influence cooperation and group-living is largely unknown. SELFRELIANCE fills this void and elucidates the functional and dysfunctional effects of (increasing opportunities for) self-reliance. Conceptualizing cooperation as a conflict between 'communalism' and 'individualism' reveals a heretofore neglected social dilemma and shows (1) how self-reliance changes the interdependence structure of groups, (2) how such changes influence the ability to solve shared problems, (3) affect norms of trust and responsibility, and (4) give rise to institutions able to solve the dilemma between independence and collective action. To this end, SELFRELIANCE is built on a new collective action model. Using this model as the theoretical bedrock, the strengths of three methodological approaches are combined: laboratory experiments (WP1/1PhD), a large-scale cross-cultural study (WP2/1Postdoc), and computer simulations (WP3/1PhD). In combination, this approach will reveal how self-reliance changes the normative foundation of groups, how cross-cultural differences in interdependence influence cooperation around the globe, and the co-evolution of self-reliance, institutions, and collective action. Results will advance our theoretical understanding of human cooperation and inform policies for promoting cooperation towards shared socio-economic problems across societies.

Immigration has generated backlash and policy instability across democracies. What determines such attitudes? This project examines whether public opinion on immigration in the United States, Germany, Sweden, and South Korea is primarily shaped by fairness perceptions (rules adherence, humanitarian needs, immigrant contributions), cultural identity threats, or economic competition fears. Using experimental surveys, the study will evaluate these factors systematically across cases. Clarifying the dominant drivers of immigration attitudes can help manage immigration-related conflicts and inform policies that are fair, politically sustainable, and consistent with democratic values.

On the crossroads between China, India and the Eurasian Steppes, the Tarim Basin in present-day Northwest China was a crucial part of the famous Silk Road trading network. Today, the main languages of the area are Uyghur and Mandarin, but numerous manuscript finds are proof of a past rich in entirely different languages. Next to literary languages like Sanskrit, the local vernaculars were Middle Indic, Tocharian, and the Iranian languages Khotanese and Tumšuqese. All Indo-European and hailing ultimately from the west, these languages show the effects of intricate patterns of long-term influence, thus forming a network of linguistic contact: the Silk Road Language Web. The interpretation of this intriguing linguistic complex has been dominated by the narrative that the Tocharians are to be identified with the Bronze Age “Tarim Mummies”, to the detriment of other groups. However, in concordance with genetic evidence, the linguistic findings of the PI’s ERC-Starting Grant and NWO-VIDI projects show that the Tocharians arrived much later, while the Iranians arrived earlier and spread over a larger area than previously assumed. Thus, an entirely new approach to the linguistic past of the Tarim Basin is called for. Based on the evidence from long-term language contact contained in the Silk Road Language Web, this project will unravel the linguistic past of the Tarim Basin to make a groundbreaking contribution to the linguistic and migrational prehistory of Eurasia. Reconstructing the dates of the splits and spreads of Khotanese, Tumšuqese and Tocharian, it will establish their routes and dates of entry into the Tarim Basin. Further, Khotanese and Tocharian vocabulary of unclear origin will be scrutinised for traces of languages of the earlier Bronze Age populations. Finally, the linguistic developments will be followed into historical times, tracing how the attested languages were eventually shaped by the later formative impact of Middle Indic and Middle Iranian.

How do hexatics flow? Forty years after Nelson’s and Halperin’s first prediction of the existence of this phase of two-dimensional matter, intermediate between crystalline solid and isotropic liquid, this seemingly elementary question is still unanswered. Whereas the delicate nature of hexatics could partially justify this oversight, recent findings in tissue mechanics have created the urgent demand to fill this gap, by providing this phase with unexpected biological relevance. Like two-dimensional crystals on the verge of melting, tissues are often neither ordered solids nor disordered liquids, but inhabit a continuum of intermediate states known as the epithelial-mesenchymal spectrum. This versatility lies at the heart of a myriad of processes that are instrumental for life, such as embryonic morphogenesis and wound healing, but also of life-threatening conditions, such as metastatic cancer. Understanding the physical origin of these mechanisms requires going beyond the current hydrodynamic theories of complex fluids and introducing a new theoretical paradigm, able to account for hexatic order and biomechanical activity. This multidisciplinary program aims to develop a systematic theory of hexatic hydrodynamics and use it to gain insight into the physical mechanisms underpinning the dynamics of tissues and the progression of metastatic cancer. The program will consist of three themes. First we will develop the necessary formalism to describe viscous flow in hexatics. Next, we will extend it to tissues and investigate the interplay between hexatic order, activity, topological defects and flow. Finally, we will use the new framework to explore the first three steps of the metastatic cascade: 1) the detachment of clusters of mesenchymal cells from the primary tumour; 2) their subsequent invasion of the extracellular matrix; and 3) their translocation across blood vessels, which allows metastases to enter into the bloodstream and disseminate to distant organs.