| Chapter 1: | An Introduction to Polarity, Ambiguity, and Kinship |
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and virtually all mouse genes have human homologues. This homology has led to the involvement and now high participation of rodent animals in the laboratory, wherein rats and mice act as stand-ins for human bodies. At the level of basic biology, rats, mice, and humans are all mammals. Each gives birth to living young and eats similar foods—and even tends to access these foods in the same domains, because rats and mice dwell wherever humans are to be found, and in people’s domestic dwellings and food production and storage facilities, rats and mice frequently access their foodstuffs. Resultant of our homologous basic physiology, similar organs, and similar body plans, we suffer from the same diseases. We each control our body chemistry using similar hormones, we each have nervous systems that work in the same way, and we all react similarly to infection and injury.
Rats, particularly, are also homologues for human minds. Rats, like humans, seem to have the capacity to carefully weigh the costs and benefits of making decisions. A 2006 study published by van den Bos, van der Harst, Jonkman, Schilders, and Spruijt in Behavioural Brain Research was the first to demonstrate this behaviour in nonhuman animals. The study found that rats weighed the benefits of obtaining a food treat against the effort that was required to obtain it. After a certain point, rats recognised that the treat was not worth the effort, and they satisfied themselves with a smaller, easier-to-obtain treat. The study found that the laboratory rats seemed to behave according to an internal constant standard, a relative ratio for each situation by which choices are measured. Because the standard varied depending on the situation, it was at least partly created by individual rats as they experienced various situations. Behavioural neuroscientist John Salamone also found in his studies of effort-related processes, such as how much energy an individual will put out to obtain a reward, that expending high effort for a low or negligible reward could be linked to depression—and that rats and people share the capacity to suffer from depression. It is even possible that rats share with humans a capacity for metacognition, a capacity that was once thought to be unique to humans and higher primates (Salamone, Correa, Mingote, Weber, & Farrar, 2006).