Refers to a type of learning where an organism forms an association between feelings of sickness and (usually) a particular food. As a consequence of this learned association, the organism avoids that food in the future. This learned association violates the usual principles of conditioning in that it is formed after only one experience of the food–sickness combination, and is extremely resistant to extinction. Most organisms show ‘bait shyness’, a hesitancy to sample new or unusual food. If a food is toxic in some way, they must learn to avoid such foods in order to survive. Organisms that can make such rapid associations are more likely to survive and pass on their genes to the next generation. This behaviour is shaped by natural selection, and is seen as an example of biological preparedness.