When Steve was about 12 years old, he read a study that measured the locomotion efficiency of different species. At the very top of the list was the condor, who expended the least amount of calories to travel. Humans, on the other hand, came in an unimpressive third of the way down the list.
Steve points out that someone at Scientific American took a look at the efficiency of locomotion of a human on a bicycle which blew away all other forms of animal powered locomotion. After all, the bicycle is the most efficient human powered machine for locomotion.
It's an interesting metaphor since it seems so accurate – it's the amplification of human ability.