Is it wrong to intervene in biological processes? Human intervention in the living world gives rise to controversies where scientists are criticised for working on biotechnologies and physicians for ending life when a terminally ill patient is experiencing unmanageable suffering. This lecture will explain the perpetuation of political controversies by showing that scientific and moral assessments of human intervention in the living world are unsolvable because they are based on cognitive biases. Looking at case studies of such controversial issues (end of life intervention, GMOs and synthetic biology debates), my analysis will focus on the apparent clarity of the double contrast between natural beings and artificial objects on the one hand, and risk and realms of uncertainty on the other. The interesting point here is that the relationship between scientific expertise and political issues is clearly related to these implicit epistemological prerequisites.