Abstract

A common picture of evolution by natural selection sees it as a process through which organisms change so that they become better adapted to their environment. However, agents do not merely respond to the challenges their environments pose. They modify their environments, filtering and transforming the action of the environment on their bodies A beaver, in making a dam, engineers a stream, increasing both the size of its safe refuge and reducing its seasonal variability. Beavers, like many other animals, are ecological engineers. They act to modify the physical challenges posed by their environment. Nests, burrows and other shelters reduce the impacts of adverse weather and of other agents. Animal also modify their exposure to biological risks. Hygienic behaviour reduces the impact of disease. Intensive grooming; moving to new roosts; using a