Anyone who has ever trained animals has wondered what animals learn from different experiences. For instance, a person walks into a pen of animals that have just been fed, catches a lamb or calf, and puts a balling gun containing a capsule with a toxin down its throat. Soon the animal will experience gastrointestinal illness, but will the animal associate the illness with the person who just caught it or with the food it just ate?
Pre-eminent psychologist John Garcia pointed out that, “All organisms have evolved coping mechanisms for obtaining nutrients and protective mechanisms to keep from becoming nutrients.” Animals learn about the consequences of eating foods or being at a particular location through two different defense systems. For many birds and most mammals, sight and hearing are associated with feelings of pain or comfort and are associated with the skin-defense system. The taste of food and feelings of nausea and satiety are part of the gut-defense system. Odors may be associated with either the skin- or gut-defense systems. The smell of predators can warn the skin-defense system, while the smell of a food serves as a cue for the gut-defense system.
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