Are you someone who is always anxious or suffers from anxiety disorder? Do you ever wonder why you feel the way you do? Well, evolutionary theory is used to explain a lot of human behaviours, including anxiety. Many of these behaviours are adaptive; however, some researchers argue otherwise. Anxiety is the body’s natural response to stress. It is characterized by feelings of tension, worry, and nervousness about an imminent event. 

To date, there are no definitive causes for anxiety disorders, and no concrete evidence to suggest why some people develop them, while others do not. On the basis of evolution, it can be argued that anxiety is an adaptive trait, meaning it aided our ancestors in survival and, therefore, became a dominant trait that was passed on over time. 

There are numerous studies and reviews in the literature to support this claim. A potential adaptive anxiety is social anxiety where an individual worries or stresses over how others socially evaluate them, which leads to fears of ostracization and exclusion from social groups [1]. It has been suggested that social anxiety is an adaptation because it prevents individuals from committing acts that would lead to social exclusion. Instead, it encourages people to strive towards social acceptance, which facilitates survival. Namely, group living ensures better protection from danger, collective accomplishments and coping mechanisms with difficult tasks, and sharing of resources [2]. 

However, in modern society, people are interacting temporarily with a wide variety of individuals, consisting mostly of acquaintances or strangers. This discrepancy in our ancestral and modern environments may lead to some people developing social anxiety [1]. Individuals who experience social anxiety may choose to avoid participating in activities or events that would lead to shame, rejection, or embarrassment. This correlates with the idea that our ancestors would have had to experience the same feelings because otherwise they would be excluded from social groups, and this would have a detrimental impact on their survival [1]. Social anxiety promotes individuals to maintain a certain level of social acceptance in valued groups and heightens concerns over possible rejection. 

There is evidence that the need for social support and inclusion is grounded in biology. Specifically, oxytocin has been shown to play a role in reducing anxiety and fear in a variety of studies, which is seen in instances of social inclusion. Oxytocin is a hormone produced in our brain that plays a role in social bonding and is often referred to as the ‘love hormone’. This phenomenon was studied in a double-blind study where both the participants and the researchers were unaware of which experimental group the participants were placed in. Participants were randomly assigned to either receive oxytocin through the nose or a placebo before experiencing stress, and either obtained social support from a friend or received none at all [3]. This social support came in the form of a friend being present and engaging with the participant, compared to the placebo where the participant was alone. Results showed that the participants who received social support and oxytocin experienced the lowest cortisol (stress) levels during stress exposure, while participants who received no social support (placebo) showed the highest levels (see Figure 1). 

Furthermore, animal research shows that oxytocin modulates the autonomic fear response (also known as fight-or-flight response). Studies done in humans to replicate these results show that oxytocin has an inhibiting effect on the amygdala, which is the region of our brain responsible for manifesting fear [3]. Not only that, oxytocin is also involved with regulating social approach behaviour, social affiliation, and attachment [3]. This information was extrapolated from animal studies that demonstrate oxytocin and other hormones having implications in mating, pair-bonding, and adult-infant attachment [3]. However, further studies would be needed to make this claim more convincing in humans, seeing as many studies have only been done on animals. Overall, oxytocin is involved with reducing social anxiety and the effect is amplified when social support is available. This further supports the idea that anxiety is adaptive, stemming from the human need for social inclusion and support.

Separation anxiety is a form of anxiety experienced by infants and young children undergoing separation, or when there is the threat of being separated from their primary caretaker. This form of anxiety is argued to be adaptive, as it has an evolutionary basis. From this point of view, it would make sense that an infant would experience stress and anxiety when separated from their mother because they would no longer feel safe. This type of ‘stranger anxiety’ is adaptive because it enables the infant/child to turn away from potentially dangerous people and keep a close distance between themselves and their mother [2]. In many cases where infanticide is probable, it is beneficial for the infant to stay closer to their biological mother. Studies done by Daly and Wilson, who are considered founders of evolutionary psychology, show that the rates for infanticide (children under the age of two) are the highest when the child lives with a stepparent. The risk is 40 to 100 times higher than for children living with both biological parents [2]. In these cases, if the child is living with their biological mother and a stepfather, then separation anxiety from the mother would be beneficial for the child. Motherly instincts prompt mothers to shield their children from stress, which means the mother is less likely to leave the child for long periods of time. This decreases the chances of any harm being inflicted on the child. 

Further animal studies show that infanticide is common in lions when new males take over a pride of females with cubs. New male lions would attempt to kill the cubs, ensuring the females do not waste their time nursing cubs that are not genetically related to them. They would mate with the females to produce their own offspring, so the females exclusively take care of their offspring and not another male’s [2]. In these cases, it makes sense for the cubs to evolve separation anxiety and always stay in close proximity to their mothers in order to decrease their chances of being killed by newcomer males. 

Despite all the evidence available in the literature that point towards anxiety as an adaptive behaviour, there is some contradictory information. It has been argued that phobias, a type of anxiety disorder, are not adaptive. Behaviours of anxiety, such as intense, irrational, and debilitating fear are challenged to not be adaptive as they do not aid the individual in any way. For example, a study showed that socially anxious children spend a long time surveilling their environment for potential threats to avoid difficult situations [4]. This, however, amplifies their social anxiety because it prevents them from learning how to manage and regulate their anxiety in challenging social situations (see Figure 2). 

Determining whether anxiety is adaptive or not can provide new outlooks in the field of psychology, and potentially devise new treatment options for symptoms of anxiety disorders. There is valid research supporting both sides, which calls for further in-depth study in order to truly determine the most accurate theory. Further human research could have major implications in psychiatry and medicine because it would provide insight on new possible causal mechanisms of various anxiety disorders.  

All in all, there is convincing evidence supporting anxiety as an adaptive human behaviour. Therefore, the next time you feel anxious or get hit with an anxiety attack, know that you are not alone and that it is not your fault. It is important to note that the course of evolution is out of our control and understanding the evolutionary pathway of anxiety is a step towards reducing the blame on ourselves. 

If you, or someone you know, is dealing with anxiety and needs support, be sure to visit the National Alliance on Mental Health or the Anxiety and Depression Association of America for valuable information on the nature of this condition as well as helpful tips on coping mechanisms. 

References

[1] Maner, J. K., & Kenrick, D. T. (2010). When adaptations go awry: Functional and dysfunctional aspects of social anxiety. Social Issues and Policy Review, 4(1), 111-142. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3161122/

[2] Buss, D. M. (1990). The evolution of anxiety and social exclusion. Journal of Social and Clinical Psychology, 9(2), 196. https://labs.la.utexas.edu/buss/files/2015/09/Evolution-of-anxiety-and-social-exclusion.pdf

[3] Heinrichs, M., & Domes, G. (2008). Neuropeptides and social behaviour: Effects of oxytocin and vasopressin in humans. Progress in Brain Research, 170, 337-350. http://portal.uni-freiburg.de/psychologie/abteilungen/psychobio/team/publikationen/ProgBrainRes_08.pdf

[4] Muris, P., Merckelbach, H., Gadet, B., & Meesters, C. (2000) Monitoring and anxiety disorders symptoms in children. Personality and Individual Differences, 29(4), 775-781. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544.7434&rep=rep1&type=pdf