We’re all aware that the ‘normal’ temperature of our bodies is 37ᵒ C or 98.6ᵒ F. Any reading on a thermometer placed under your tongue that exceeds this mark spurs apprehension — it is a symptom of a fever. However, this fact must not be treated as gospel. For instance, an oral temperature of 100ᵒ F before bedtime is speculated to be safe, while a temperature of 99ᵒ F in the cavity of your armpits in the morning rouses suspicion.
So, while there might not be a normal temperature, there is surely a normal range. There is a consensus that a body whose temperature is measured to be greater than 100.4ᵒ F is suffering from a fever. However, it is extremely odd or peculiar that our bodies exist, if not at a particular temperature, then within a particularly narrow range of temperatures. Why does the human body maintain this and this temperature only?
If We Were Colder
Cold-blooded animals, such as reptiles and amphibians, are known to be some of the most common prey of abject fungal infections. Contrast their plight with the immunity of warm-blooded animals – while cold-blooded animals are prone to tens of thousands of fungal species, warm-blooded mammals are only prone to about one hundred of them. It seems that the latter, which includes us, have triumphed due to an elevated body temperature.
Arturo Casadevall, a professor and chair of microbiology and immunology at Albert Einstein College of Medicine of Yeshiva, recently found that the plethora of fungal species that can infect an organism decline by 6% for every 1.8ᵒ F rise in temperature. This statistic perfectly explains why mammals evolved to incorporate an increased body temperature. It provided us an edge over our colder ancestors, thereby promoting and cementing our position as the most dominant species on the planet. If we were colder, we would be more susceptible to fungal infections and therefore death.
If We Were Warmer
A warm body deters fatal fungal infections, but an increase in temperature can only be maintained with an increase in metabolism. The energy required to heat our body is generated by consuming food. The food we consume is essentially broken down by the body to extract its energy to drive the hydraulic and pneumatic machines that are our organs.
To further reduce the possibility of attracting a fungal infection, we would have to exist at even higher temperatures, but this would require us to forage and consume more and more food to meet the increased energy demand or the new metabolism rate. The physical constraints of a mammal therefore put a ceiling on its body’s temperature.
A compromise must be made between the myriad fungal infections a mammal can deter and the food (energy) it can afford. In a new study, Casadevall and biologist Aviv Bergman of the same institute analyzed the fungi-resistant capabilities acquired by maintaining a body temperature between 86ᵒ F – 104ᵒ F in contrast with the food that must be consumed to keep the fire burning. They found the optimal temperature to be 98.06ᵒ F! The outcome is just marginally astray from our normal temperature of 98.6ᵒ F. In fact, it might be much closer to it, as some researchers claim the true normal temperature may actually only be 98.2ᵒ F.
The normal body temperature can be different for different mammals in accordance with their needs. For instance, the normal temperature of a rabbit is around 104ᵒ F, which is much warmer than the optimal temperature of the majority of mammals. However, the authors concluded that, essentially, the most advanced mammals have settled on temperatures that lie within the 96.8 – 104ᵒ F or 36 – 40ᵒ C range.