Environmental policy has a size bias. Small organisms, such as microorganisms, command less attention from environmentalists than larger organisms, such as birds and large mammals. A simple thought experiment involving microscopic polar bears and giant microorganisms illustrates the importance of size in environmental ethics. Given the positive correlation between body size and brain size, there is probably a basis for a size bias in environmental ethics using ethical frameworks based on conations. This paper examines the relevance of the size of (...) organisms in environmental ethics. It emphasizes the need to understand the theoretical reasons for the importance of size, and not to base a size bias merely on a subjective anthropocentric prejudice favouring large organisms. (shrink)