What makes rat studies relevant to understanding human biology?

Rodents are frequently chosen for research due to their practicality: they are inexpensive, abundant, and compact. While organisms like fruit flies and mice are also lab favorites, rats are particularly valuable for studies requiring larger subjects, such as surgical procedures [source: NCI].

You might frown at the idea of rats being useful, given their reputation for being messy and intrusive. However, evolutionarily, rats are surprisingly close to humans. Around 80 million years ago, rodents and primates diverged from a common mammalian ancestor, making rats more similar to us than mice in terms of brain function [source: National Human Genome Research Institute].

Interestingly, the rat genome mapping reveals that specific regions of rat DNA evolve faster than those in mice. Rats possess unique genes related to immunity, pheromone production, and protein and chemical processes [source: National Human Genome Research Institute].

This genetic similarity is a significant advantage for humans: rats have equivalents for every human gene linked to diseases. A 2013 study highlighted that rats, unlike mice, fully replicate the brain changes seen in Alzheimer's. Mice failed to show the same level of brain cell deterioration observed in humans. However, rats with age-related health issues mirrored human brain responses, developing cell tangles and losing neurons [source: Hamilton].

Another reason rats are valuable in human studies is the 2014 U.S. National Institutes of Health mandate requiring equal numbers of male and female rats in funded research. Previously, male rats were predominantly used due to concerns about female rats' estrus cycles. However, recent studies confirm that female cycles do not disrupt research, and male rats exhibit similar variability [source: Prendergast].