One of the first theories of metabolic rate linked energy with the surface area. Biologists used a paint roller to swipe a subject's body, counting the stripes left behind to calculate the total surface area. It was originally designed for use on cows, but in the 1920s Hannah Stillman Bradfield performed this experiment on 40-odd naked female students. There are pictures of the device in use on a cow, but sadly Bradfield's great moment in science seems to have gone un-photographed. Across species, if you know an animal's size you can make a good guess at the number of offspring it will have: small animals have big litters, large ones have only a few. But humans seem to have far fewer offspring than their body size would predict. However, if you consider our external metabolism--all the energy we use in our houses, cars, going out, and so on--and if you add this energy to our biological metabolic rate, it turns out a western person uses as much energy as a 30-ton gorilla would.