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Your body is really good at keeping its temperature at around 37° C, but have you ever wondered why?

Hosted by: Michael Aranda
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[SciShow intro plays]
[Text: QQs: Why is my body temperature 37 degrees?]

Michael: If you pulled out a thermometer and took your temperature right now, you’d probably get a reading of around 37 degrees Celsius. That number may vary a little from day to day, or even hour to hour, but overall your body temperature is pretty consistent.

If you get too hot, your blood vessels will expand, and you’ll sweat to cool down. If you get too cold, your blood vessels will contract, and you’ll shiver to warm up. And if you stray more than a couple degrees in either direction -- like with a really bad fever or in freezing weather -- your proteins and cells stop working, and you could die.

So why is 37 degrees the magic number? Why not 35 or 40? Well, one major theory suggests it’s all about keeping out fungus. Scientists have found that certain animals, like reptiles and amphibians, get a lot of different fungal diseases. And they’re all ectotherms -- they depend on external heat sources to stay warm. Specifically, they get way more fungal infections than their endotherm counterparts, like mammals, which generate body heat internally.

Researchers from Yeshiva University wanted to find out why. They tested the heat tolerance of different species of fungus, starting at a temperature of 30 degrees Celsius. And found that every one degree increase in temperature caused a six percent decrease in the number of fungal species that are able to infect an animal host. So if you’re a frog depending on sunlight to warm you up, you’ve gotta worry about tens of thousands of fungal species that can infect you and cause life-threatening disease. But if you’re a mammal hovering around 37 degrees, only a few hundred fungi can survive long enough to mess with you.

In other words, when it comes to the risk of fungal infection, it really helps to be hot. Then again, you don’t want to be too hot. After all, it takes a whole lot of energy to maintain a high body temperature, and you don’t want to spend all your time finding food and eating it. You want to find a perfect balance. And guess what? When these researchers ran some mathematical models, weighing the benefits of protecting against fungi versus the costs of extra food consumption, they calculated an ideal body temperature... of 36.7 degrees Celsius. Which is right around our toasty 37 degrees.

In fact, these scientists even think that maintaining this warm body temperature helped mammals thrive as the dinosaurs went extinct, even though it’s energy-intensive. It’s possible early mammals started to beat out reptiles simply because we were more resistant to fungus. So, I guess, our hotness has helped us survive.

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