“It is worth asking why such an apparently simple device as the bicycle should have had such a major effect on the acceleration of technology. The answer surely lies in the sheer humanity of the machine. Its purpose is to make it easier for an individual to move about, and this the bicycle achieves in a way that quite outdoes natural evolution.
When one compares the energy consumed in moving a certain distance as a function of body weight for a variety of animals and machines, one finds that an unaided walking man does fairly well (consuming about .75 calorie per gram per kilometer), but he is not as efficient as a horse, a salmon or a jet transport. With the aid of a bicycle, however, the man’s energy consumption for a given distance is reduced to about a fifth (roughly .15 calorie per gram per kilometer).
Therefore, apart from increasing his unaided speed by a factor of three or four, the cyclist improves his efficiency rating to No. 1 among moving creatures and machines.” (S.S. Wilson from Scientific American, March 1973)
(see this link, via futility closet)