For hundreds of years, people have looked to animals and plants to explain elusive human phenomena. Aesop’s fables and ancient texts highlight the extent of this human-animal relationship. In these didactic stories, the whimsical portrayal of animals and plants is used to illustrate and concretize human action. Aside from human imagination, animals and plants have also played a significant role in unraveling human’s inner complexities.
Gregor Mendel began to investigate pea plant patterns of inheritance in 1856 (1). After 10 year of breeding thousands of generations of Pisum sativum, Mendel discovered the basis of modern genetics. He was renamed the “father of genetics”, albeit it was not until years later that his findings were deemed noteworthy. As often taught in introductory biology classes, the species that Mendel chose to study—common pea plants—was the key to uncovering the principle of passing traits down generations. Pea plants display simple dominant-recessive traits that are easy to isolate and observe, making them simple organisms to study compared to the diverse and complex genetic makeup of humans. The basic rules of pea plant genetics are applicable to all organisms, however, making it a universal reality.
What makes some organisms better suited for research? Why do some organisms earn the NIH-awarded prestige of being a model organism (2)? The most common model organisms are the mouse, rat, budding yeast, zebrafish, fruit fly, and arabidopsis. It is common to see these animals populating modern research labs; we no longer question why we would use mice to study human disease. In the current scientific and technological landscape, however, it is worth analyzing the relevancy and usefulness of model organisms.
Model organisms are non-human species that are manipulated and experimented on with the objective of improving our understanding of biology, particularly in relation to humans. The underlying principle that enables researchers to use non-human organisms is that many genes and processes are conserved; therefore, discoveries about one animal can be inferred for another animal. While any species can be studied and generate fascinating findings, only certain species have representational scope, or in other words: how applicable the results are for the wider organismal body (3). Due to the extensive research on certain species and their generalizability to humans, large research communities have been built up surrounding model organisms for scientists to share their research and knowledge while also benefiting from the literature.
The benefit of animal studies resides in the ethical realms of scientific study. Many studies would be considered unethical to carry out in humans because they may involve detrimental or unknown outcomes. By breeding and sacrificing animals, humans are able to intentionally generate disease states or cause mutations with the additional advantage of being able to follow normal cellular proteins with fluorescent proteins and live imaging, as well as freedom to control the environments and schedules of the test subjects (4). Mice are particularly useful in studying certain genes or neural networks. For example, if there is a gene of interest that is being studied for its role in disease, scientists have developed highly efficient ways to genetically engineer knockout mice using CRISPR/Cas-9 technology (5). Knockout mice are individuals who have a gene that has been physically removed or chemically inhibited in order for the protein to lose its expression. Using this technique, mouse models of disease can be created to imitate human conditions. Models are useful because they allow different treatments—that would otherwise be unethical to test in humans, but could have transformative impacts on human health—to be experimented first on mice that share many physiological processes and biological similarities with humans.
The question still remains: can we trust results from animal studies to correlate with human outcomes? Model organisms are almost universally accepted in research, yet there are voices in the scientific community that challenge the unquestioning acceptance of model organisms as test animals. While mice have been used to map neuronal networks (6), their simplicity fails to reflect the genetic and physiological diversity of human cells (7). By focusing research on a few organisms, there is a natural limitation on what scientists can study and choose to study. This can lead to a “translational disconnect” (5) between development and homogeneity in animals versus the diversity and plasticity of human systems. This by no means eliminates the usefulness of model organisms, however, it does draw attention to the issue of why certain organisms are preferred over others. There are no right answers to solving the unanswered mysteries about the world and every species has distinct features that lend themselves better to addressing certain types of questions.
Whether or not a species can be considered a model organism has definite political and economic implications. It matters for scientists who see potential in unconventional research methods and models to ensure funding for uncharted territory. It comes down to which organism is the most suitable to study a particular function or process. Model organisms are just one special class of species that provide “models for whole organisms, whose potential representational scope extends to all living beings” (3). Research at the bench drives forward thinking. The combination of innovation, technology, creativity, and a building off of the past inventory drives medical advancements and improvements in patient outcomes. The fact that a humble organism like the pea plant—not a modern model organism— made such a huge impact on human history and understanding is simply astounding.
Edited by: Jessica Wu
Illustrated by: Elena Bosak