Summary

In Chapter 10 Bryson pauses from his tour of the parts of the body to discuss how humans became upright, walking and running creatures and what effects exercise has on our bodies. Out of 250 species of primates, humans are the only ones who get around on only two legs. Many theories have been proposed about how and why this came to be so. We do not know for sure, but scientists do know that walking on two legs came at a price, making us more vulnerable. Lucy, the skeleton of a protohuman found in Ethiopia 3.2 million years ago, was three and a half feet tall and weighed only 60 pounds. In 2016, scientists discovered she likely died falling out of a tree, showing that early humans probably still spent a great deal of time in the forest in trees, as our...