Summary

In Chapter 11, Bryson delves into how our bodies maintain homeostasis or equilibrium. He begins with the surface law: as the volume of an object grows, its surface area increases. This is important because the more surface area you have relative to volume, the more creatures must work to stay warm. Little animals, like mice, have to produce heat more rapidly to keep warm and thus must eat more, relative to their weight, every day. Mice have to eat 50 percent of their body weight every day to survive. Humans have to eat about 2 percent of our body weight. Mammals uses 30 times more energy than cold-blooded reptiles, which means we have to eat more.

Our body temperature rarely varies more than a degree from 98.6 degrees. If it falls two degrees below normal or four above, our brain goes into crisis. The hypothalamus in the brain...