The Selfish Bug

Our brain lives in a symbiotic relationship with the bugs in our body. Without the help of these bugs we humans would never have evolved to our current level of cognitive performance. So, what’s in it for them? Everything - their survival and the continuation of their species! Humans benefit profoundly by the inherent selfish desire of these bugs to survive.

Sometime during the Cambrian period, the ancestors of our bugs quickly discovered the survival benefits of fully integrating themselves into much more complex organisms; once there, they never left. Obviously, it is in their best interest to keep us, their large, warm, moist and environmentally-friendly vessels, mentally and physically healthy. As you will see, they do an excellent job of keeping us, their hosts, mentally fit.

Our bugs spent millennia fine-tuning a set of highly dedicated functions that provide our brains with specialized chemicals that keep us happy and relaxed. These bugs, mostly found in our gut, produce many different chemicals that influence brain function. For example, they help to convert carbohydrates in our diet into molecules that easily leave the gut and enter the brain to influence levels of the hormone BDNF that plays a critical role in the birth and survival of neurons and the ability of the brain to learn and remember.

Humans invented a class of anti-anxiety drugs called benzodiazepines over sixty years ago. One of the most famous, and financially successful, of these was the drug Valium. Recently, scientists discovered that the human body contains a molecule that is identical to Valium. This was a rather shocking discovery given that the human body is incapable of synthesizing Valium. Yet, there it was floating around inside of our brain. Apparently, synthesizing Valium is something that the bugs do easily. Scientists now believe that these bug-derived chemicals help prevent us from developing social anxiety and generalized anxiety disorder.

Our bugs also produce a novel chemical called Queuine, aka Vitamin Q, that regulates the production of the mood-controlling chemicals serotonin, dopamine and norepinephrine in our brain. Without Vitamin Q melatonin synthesis becomes impaired and the quality of sleep worsens. Without Vitamin Q the metabolism of serotonin is shifted to the production of quinolinic acid; the production of this acid is highly linked to major depression and suicide. Our suicide is definitely not in the best interest of these selfish bugs. Dosing us with adequate amounts of Vitamin Q helps to keep us from killing ourselves and undermining the survival and continuation of our bugs.

Thus, it should come as no surprise that taking antibiotics has serious repercussions on our mental health. The negative consequences of antibiotics are most profound when we, and they, are young. When pregnant mothers take antibiotics there are long-lasting changes in the composition of the offspring’s bug populations that negatively influence brain function. Frequently, because antibiotics kill our bugs so indiscriminately the population of surviving bugs becomes dominated by a few unpleasant bugs who are selfishly more interested in their own survival than in contributing to our mental fitness. When this happens, the symbiosis ends badly for both the bugs and their human vessels.

Clearly, it is the self-serving intention of our bugs to keep us happy, well-rested and relaxed so that we keep eating and having sex, two behaviors that are usually absent in people who are depressed, stressed or anxious, but are critical if our selfish bugs have any chance of thriving and surviving into the future. In a manner similar to that originally outlined by Richard Dawkins to explain the emergent behavior of our genes, our bugs behave in such a way as to increase their own chance of survival by improving the chances of survival of their large multicellular vehicle – humans. These bugs were not simply along for the ride as we became the dominant species on this planet; they made the journey possible and they expect to be compensated for their effort.

© Gary L. Wenk, Ph.D. is the author of The Brain: What Everyone Needs to Know (2017) and Your Brain on Food, 3rd Edition, 2019 (Oxford University Press).