With regard to organ donation, Germany is an 'opt-in' country, which requires explicit consent from donors. The relatives are either asked to decide on behalf of the donors' preferences, if these are unknown or if the potential donor has explicitly transferred the decision to them. At the core of this policy lies the sociocultural and moral premise of a rational, autonomous individual, whose rights require legal protection in order to guarantee a voluntary decision. In concrete transplantation practices, the family plays an even more important role. Potential donors and their families decide while being embedded in relations, a point which does still not gain full recognition. This particular discrepancy between policy and practice creates conflicts, which remain taboos of academic inquiry and public discourse. Our analysis shows a plurality of the family's role in the transplantation process, which reveals an inner tension of the organ donation system. This tension provokes epistemic opacity on the one hand and different collective strategies as responses to discursive exclusion on the other. In future deliberations about organ donation, it is important to create spaces for open discussion, but also practices of communicative engagement, which take care of the needs and emotions attached to taboos.

Possible trajectories of sustainability are based on different concepts of nature. The article starts out from three trajectories of sustainability (modernization, transformation and control) and reconstructs one characteristic practice for each path with its specific conceptions of nature. The notion that nature provides human societies with relevant ecosystem services is typical of the path of modernization. Nature is reified and monetarized here, with regard to its utility for human societies. Practices of transformation, in contrast, emphasize the intrinsic ethical value of nature. This becomes particularly apparent in discourses on the rights of nature, whose starting point can be found in Latin American indigenous discourses, among others. Control practices such as geoengineering are based on earth-systemic conceptions of nature, in which no distinction is made between natural and social systems. The aim is to control the earth system as a whole in order for human societies to remain viable. Practices of sustainability thus show different ontological understandings of nature (dualistic or monistic) on the one hand and (implicit) ethics and sacralizations (anthropocentric or biocentric) on the other. The three reconstructed natures/cultures have different ontological and ethical affinities and conflict with each other. They are linked to very different knowledge cultures and life-worlds, which answer very differently to the question of what is of value in a society and in nature and how these values ought to be protected.

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