A bicycle (or bike) is a pedal-driven, human-powered vehicle
with two wheels, one behind the other, attached to a frame. The
basic shape and configuration of a typical bicycle's frame,
wheels, pedals, saddle, and handlebars have hardly changed since
the first chain-driven model was developed around 1885, although
many important improvements have since been made, especially
since the advent of modern materials and computer-aided design.
These have allowed for a proliferation of specialized designs
for individuals who pursue a particular type of cycling. The
bicycle has affected history considerably, in both the cultural
and industrial realms. First introduced in nineteenth-century
Europe, bicycles now number over one billion worldwide,
providing the principal means of transportation in many regions,
notably China and the Netherlands. They are also a popular form
of recreation and have been adapted for use in many other fields
of human activity, including children's toys, adult fitness,
military and police appl