Body Temp Through Time: A Surprising Evolution
I would like to begin by saying that all of us have been sick at least once in our lives, and understandably, all of us have had a fever at least as often. Myself, I grew up in a household where my mom was a bit of a hypochondriac, and it extended to all family members as well. And every time my fever was down to 36.6°C, she sighed in relief, as my fever was gone, and I was past the risk zone. All my life, I have lived under the assumption that this would be the normal human body temperature; however, I’ve come to learn otherwise.
While the normal human body temperature value for healthy adults may vary in different countries, it inevitably oscillates around the 37°C area, a notion popularized by the German physician Carl Wunderlich back in 1867. However, as one can plainly see from the example above, this notion is based on outdated studies. A study done in the US by M. Protsiv, C. Ley, J. Lankester, T. Hastie, J. Parsonnet, called “Decreasing human body temperature in the United States since the Industrial Revolution”(2020), has determined that the average human body temperature has had a steady decline over the last two centuries in the United States, which coincides with an overall improvement of the quality of life, such as medical advancements that decreased infection probability, and increased the average life expectancy. While people that have a high physical activity job may still present with a higher body temperature, the average human body temperature has gone down to approximately 36.5°C. These studies have come to the assumption that decreased physical activity, changes in the human body composition and antibiotic usage are potential causes of this temperature decline.
Body temperature reflects a combination of multiple factors, such as physiological processes such as cellular metabolism, immune function, disease state, and thermal exchange between the body and the environment. Therefore, as overall life conditions have improved in most areas of the world, the human body has less pathogens and infections to fight off on its own, and a decreased physical activity has resulted in a slower metabolism; these factors contribute to a lower human body temperature.
There is another factor that is theorized to contribute to the change in normal human body temperature, namely the change in global temperature. Unfortunately, there aren’t sufficient studies on this specific area that would all come to a common conclusion. That being said, while a lot of people are currently preoccupied with the global warming phenomenon, certain studies show that while the range of temperature variation on a worldwide scale has grown wider since the inauguration of the Industrial Age, the average temperature has also risen on a commensurate rate, by around 1.8°C since 1850. This may contribute to a lesser energy expenditure towards thermoregulation, and thus a decreased body temperature.
On the topic of temperature regulation, one must also take into consideration the advancement of technology in what pertains to quality of life, such as heaters and AC units. While they do improve the overall quality of life, and are indispensable for most people nowadays, they also contribute to our spending increased time in thermoneutral zones, which in turn contributes to a lower energy expenditure to support our body’s normal thermoregulation process.
One final factor that possibly contributes to this phenomenon is a change in the normal human sleep cycle. As technology advanced and allowed us to take our lives into the night as well since the dawn of the lightbulb, our sleeping cycle has also been steadily changed to accommodate the expanded timeframe in which we operate. This disruption of our natural biorhythm came with a change in our circadian rhythm of thermoregulation, appetite and metabolism, all being factors that affect our core body temperature. However, these behavioral changes can only affect our body temperature in very limited amounts, and they revert once the normal biorhythm was restored in test groups; thus, certainly more in-depth studies are required to confirm or deny this possibility.
It is still unclear at this stage how our biology will be affected by this change, and what else may come from this in the future. It may result in a change in the human reproductive system, or other biological changes that we may not be able to predict. However, as it has been dictated from the dawn of time, every change in how a living organism operates is part of the evolutionary process. What may come of it may only be speculated at this point in time, and will be witnessed by our descendants over the course of time.
