In order to conduct scientific research, model organisms are often used which involves the studying of a non-human organism that can provide insight for human application. For example, model organisms are often used to understand human disease mechanisms, where research on humans would be difficult or unethical. To be considered a model organism, an organism must meet taxonomic equivalency, meaning that the organism was deemed to have similar enough physiology to humans in order to draw similar conclusions for humans, especially in terms of treatment (Fields and Johnston). For the application of animal research to understanding humans, it is dependent on the evolution and common descent of all organisms. As different organisms diverged, many of the metabolic, genetic, and developmental pathways remain conserved, which is why similarities can be drawn (Fox). This has been a long-standing practice of scientific research dating as far back as Aristotle, with the next famous scientists to use model organisms being Antoine Lavoisier and Louis Pasteur in regards to understanding germ theory (Cohen and Loew).
When selecting a model organism to work with, there are a few considerations to keep in mind. The reproduction time and number of progeny is vital so that generations can be traced over a span of time, which is important for genetic and developmental research. Organisms that have a short generation time, which means that reproduction can happen quicker is deall. Model organisms that are cheap and easy to store is also important to consider for the researcher’s perspective as it allows for more accessibility. If possible, larger embryos that are easier to see, such as by developing outside of the body, are useful (“What are Model Organisms?”).
Many different organisms fit the criteria to become model organisms, giving researchers a wide range to organisms study and work with, making discoveries and advancements to aid in understanding of human disease. Organisms that fit include: yeast (Saccharomyces cerevisiae), fruit flies (Drosophila melanogaster), nematode worms (Caenorhabditis elegans), western clawed frogs (Xenopus tropicalis), mice (Mus musculus), and zebrafish (Danio rerio).
Within model organisms, there are three types of models used: homologous, isomorphic, and predictive. Homologous disease models mean that the model organisms has the same causes causes, symptoms, and treatment as humans with the same condition. Isomorphic organisms, do not share the same cause, but share the same symptoms and treatments. Predictive models are based on only a few aspects being similar (Pinel). To classify more broadly, model organisms can be broken down into four categories: experimental, spontaneous, negative, and orphan. The most common type of this classification is experimental, which refers to models of disease that resemble human conditions in phenotype or response to treatment but are induced artificially in the laboratory. Spontaneous models refer to diseases that are analogous to human conditions that occur naturally in the animal being studied, meaning there is no laboratory manipulation and the organism can be studied as is. Negative models refer to control animals, which are useful for validating an experimental result by comparing what happens where there is no intervention. Orphan models refer to diseases for which there is no human analog and occur exclusively in the species studied (Hughes and Lang).
Learning the reasons behind why model organisms are used sets a foundation for understanding why conclusions can be drawn between animal studies for human application. If not for model organisms, scientific research would not have been able to make as many discoveries to help humans, specifically for those facing diseases. Model organisms are vital to scientific research and the lives are something to be cherished as they provide insight into humans.
Cohen BJ, Loew FM. (1984) Laboratory Animal Medicine: Historical Perspectives in Laboratory Animal Medicine Academic Press, Inc: Orlando, FL, USA; Fox JG, Cohen BJ, Loew FM (eds)
Fields, S., & Johnston, M. (2005). Whither model organism research? Science, 307(5717), 1885-6. Retrieved from https://search-proquest-com.remote.slc.edu/docview/213611958?accountid=13701
Fox, M. A. (1986). The Case for Animal Experimentation: An Evolutionary and Ethical Perspective. University of California Press. Retrieved from https://books.google.com/books?id=yTfNH3cScKAC
“Pinel Chapter 6 – Human Brain Damage & Animal Models”. Academic.uprm.edu. Retrieved 2014-01-10.
What Are Model Organisms?” Facts, The Public Engagement Team at the Wellcome Genome Campus, 3 Mar. 2017, http://www.yourgenome.org/facts/what-are-model-organisms.