Written by: Dorrie Peters

As this semester reaches a peak, many students will begin to experience heightened anxiety revolving around coursework, college applications, and social events. According to the National Institutes of Health, roughly one-third of teenagers suffer from a serious anxiety disorder and many more develop various symptoms of anxiety from daily stressors. Given that humans are so closely related to other members of the animal kingdom, it would seem natural that other organisms on earth experience similar mental inflictions to humans. While they may never encounter the struggles of high school, wild animals face their own unique stressors such as escaping predators or scavenging for sustenance. But where does anxiety come from, and why does it afflict humans in such primitive ways? The answer lies in the evolution of the limbic system.

The Limbic System

To understand the mystery of anxiety in humans, it is essential to first locate where anxiety resides in the brain. While severe anxiety can affect nearly every corner of the body, its main home is in the limbic system, which is a combination of regions in the brain that monitors all emotional and behavioral responses. Though definitions of the limbic system vary, many neurology professionals agree that it consists of five core areas: the cingulate gyrus, the thalamus, the hypothalamus, the amygdala, and the hippocampus. Most animals have some kind of limbic system, although not all are as developed as that of the human brain.

Figure 1

Diagram of the various parts of the human limbic system

Source: Lumen Learning Biology for Majors II

For example, the limbic systems in dogs are very closely related to our own, alluding that dogs experience emotions in similar ways to humans. On the other hand, the limbic systems in amphibians such as frogs are arranged in a completely different manner. So, while modern technology does not allow scientists to examine the thoughts and feelings of another species, the drastic contrast in the layout of a frog’s limbic system implies that they process fear and emotion differently than humans.

The Amygdala and Anxiety

Individuals with anxiety disorders experience heightened activity in the limbic system when the brain perceives a social threat. This causes the amygdala, the node in the brain that is in charge of processing fear and emotion, to become hypersensitive and disregard certain limits within the body. For example, many people develop shortness of breath or rapid heart rate during periods of anxiety. These symptoms arise because the amygdala overestimates the severity of a threat. 

Evolution

The common symptoms of anxiety in humans — hyperventilation, increased heart rate, and sweat — may be a nuisance, but they stem from an important survival mechanism that was passed down through evolution. The same manifestations of anxiety that plague humans are remarkably useful to animals in the wild. When faced with the threat of a predator, these responses from the amygdala are designed to aid an animal in escape. Quick breathing, bursts of adrenaline, and a racing heartbeat are all useful tools that increase efficiency and speed. Due to natural selection — an evolutionary process also known as “survival of the fittest” – organisms with highly reactive amygdala responses lived to pass on this trait, eventually transferring it to humans.

Figure 2

Prey evading a predator using responses from the amygdala

Source: Digital Safari, CGTN

Conclusion

When one looks at the limbic system, it becomes evident that anxiety in humans is a lingering effect of evolution and survival of the fittest. Given that humans have progressed beyond daily threats of hunting and being hunted, the fear responses produced by the brain seem outdated and bothersome. While these biological responses may have been useful for the survival of our wild ancestors, they are usually a burden to us. Modern-day humans face their challenges in a different way, so while there may not be the need to run from predators or hunt for food, the stress of high school is a wilderness of its own.

References and Sources

Campbell, G. (2009, March 16). Does the Limbic System Exist? Brain Science Podcast. Retrieved September 17, 2021, from https://brainsciencepodcast.com/bsp/2009/3/16/does-the-limbic-system-exist.html

Karasewich, T. A., & Kuhlmeier, V. A. (2020, March). Trait social anxiety as a conditional adaptation: A developmental and evolutionary framework. Developmental Review, 55. https://www.sciencedirect.com/science/article/pii/S027322971930125X?casa_token=VKbnFAIPXN4AAAAA:sPGcP_mqjV70_oYreyDh2EdGRwRFFjLjWOfJNyCORsR7sJBGg80ECeSwnsSxJ8_QowKRMvfXYQ#b0640

Martin, E. I., Ressler, K. J., Binder, E., & Nemeroff, C. B. (2009, September). The Neurobiology of Anxiety Disorders: Brain Imaging, Genetics, and Psychoneuroendocrinology. Psychiatr Clin North Am, 32(3), 549-575. 10.1016/j.psc.2009.05.004