Why Is 98.6ºF (37ºC) a Normal Body Temperature?

Nobody knows exactly why body temperature is relevant to so many of the processes in the body that it must be a compromise, struck on by evolution, between the best temperatures for a variety of needs. It’s easy to see that there is no reason for 98.6ºF (37ºC) precisely because different species of mammals have different normal body temperatures, ranging between about 97ºF (36ºC) and 103ºF (40ºC). In fact, the normal human body temperature is not exactly 98.6ºF; that number is the exact conversion of 37ºC, which was not intended to be exact within a degree in either direction because normal human body temperature ranges between about 36-38ºC or 97-100ºF.

Anyone who’s ever upped their exercise routine should be familiar with the first balance struck by body temperature. A high body temperature comes from burning fuel more quickly, making an organism able to move more quickly and put out more effort, but also requiring it to consume more fuel. So, that’s the first compromise – between the value of having more energy and the cost of having to find more food. Normal human body temperature varies throughout the 24-hour cycle, serving our energy needs; it’s coolest in the early morning, rises after wake-up, and reaches a high point in the afternoon. Many mammals have more constant body temperatures; perhaps this shows that humans have always followed something close to the daily schedule most have now.

Another determinant of body temperature is chemistry – different chemical reactions proceed at different rates, or not at all, depending on temperature. So all the chemical interactions in the human body – the activity of enzymes, the construction of proteins, the conversion of glucose into energy, and so on – need to go on at the right rate, relative to many other processes that also vary, in order to keep us functioning and healthy. This is probably another reason that all mammals have body temperatures between about 96 and 103ºF; our bodies are similar enough to those of whales and mice to make that range the best for all of us.

In this light, it is interesting that there is something universally significant about the center of that range; 38.2ºC / 100.8ºF is the “Phi” point between boiling and freezing – about 3/5 of the way from freezing to boiling. “Phi” is the “golden ratio,” a number (really a relationship) that appears throughout nature in many guises, such as in patterns of leaves, branches, bones, and crystals. Phi’s presence in natural shapes is not as surprising as it showing up as the temperature of mammalian life. But, nobody knows of just one reason that it is a better point for body temperature than say, ½ way between freezing and boiling. Researchers have noted that it’s hot enough to discourage fungal growth but not so hot as to demand too much food. But there must be many other factors that make 98.6ºF ideal for humans. We assume that if we compared the effects of temperature on all sorts of different bodily processes, we would discover that 98.6ºF (more-or-less) strikes an ideal balance.

Quotes

“The body is a house of many windows: there we all sit, showing ourselves and crying on the passers-by to come and love us.” – Robert Louis Stevenson

“There are two different types of leader. A person can either be like a thermometer or a thermostat. A thermometer will tell you what the temperature is. A thermostat will not only tell you what the temperature is, but it'll move you to the temperature you need to get to.” – Kevin McCarthy