Psychologists study animals for a variety of reasons. Sometimes they study the behavior of a particular animal in order to solve a specific problem. They may study dogs, for example, to learn how best to train them as watchdogs, chickens to learn how to prevent them from fighting one another in henhouses, and wildlife to learn how to regulate populations in parks, refuges, or urban areas. These are all examples of what is called applied research.
Most psychologists, though, are more interested in human behavior but study animals for practical reasons. A developmental psychologist, for example, may study an animal that has a much shorter life span than humans so that each study takes a much shorter time and more studies can be done. Animals may also be studied when an experiment requires strict controls; researchers can control the food, housing, and even social environment of laboratory animals but cannot control such variables in the lives of human subjects. Experimenters can even control the genetics of animals by breeding them in the laboratory; rats and mice have been bred for so many generations that researchers can special-order from hundreds of strains and breeds and can even obtain animals that are as genetically identical as identical twins.
Another reason psychologists study animals is that there are fewer ethical considerations as compared to research with human subjects. Physiological psychologists and neuropsychologists, in particular, may utilize invasive procedures (such as brain surgery or hormone manipulation) that would be unethical to perform on humans. Without animal experimentation, these scientists would have to do all their research on human victims of accident or disease, a situation which would reduce the number of research subjects dramatically as well as raise additional ethical considerations.
A number of factors make animal research applicable for the study of human psychology. The first factor is homology. Animals that are closely related to humans are likely to have similar physiology and behavior because they share the same genetic blueprint. Monkeys and chimpanzees are the animals most closely related to humans and thus are homologically most similar. Monkeys and chimpanzees make the best subjects for psychological studies of complex behaviors and emotions, but because they are expensive and difficult to keep, and because there are serious ethical considerations when using them, they are not used when another animal would be equally suitable.
The second factor is analogy. Animals that have a similar lifestyle to humans are likely to have some of the same behaviors. Rats, for example, are social animals, as are humans; cats are not. Rats also show similarity to humans in their eating behavior (which is one reason rats commonly live
around human habitation and garbage dumps); thus, they can be a good model for studies of hunger, food preference, and obesity. Rats, however, do not have a similar stress response to that of humans; for studies of exercise and stress, the pig is a better animal to study.
The third factor is situational similarity. Some animals, particularly domesticated animals such as dogs, cats, domestic rabbits, and some birds, adapt easily to experimental situations such as living in a cage and being handled by humans. Wild animals, even if reared from infancy, may not behave normally in experimental situations. The behavior of a chimpanzee that has been kept alone in a cage, for example, may tell something about the behavior of a human kept in solitary confinement, but it will not necessarily be relevant to understanding the behavior of most people in typical situations.
By far the most common laboratory animal used in psychology is Rattus norvégiens, the Norwegian rat. Originally the choice of the rat was something of a historical accident. Because the rat has been studied so thoroughly over the past century, it is now often the animal of choice so that comparisons can be made from study to study. Fortunately, the rat shares many features with humans. Other animals frequently used in psychological research include pigeons, mice, hamsters, gerbils, cats, monkeys, and chimpanzees.
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