Shaving razor was essentially a small piece of a straight razor attached to a handle using a clamp mechanism. Before each shave the blade had to be attached to a special holder, stropped with a leather belt, and placed back into the razor. After a time, the blade needed to be honed by a cutler. In 1895, King Camp Gillette invented the double-edged safety razor, which utilised inexpensive, disposable blades sharpened from two sides. It took him until 1901 to build a working, patentable model, and commercial production began in 1903. The razor gained popularity during World War I when the
Occam's razor reject the simple hypotheses. Recent advances employ information theory, a close cousin of likelihood, which uses Occam's razor in the same way. Francis Crick has commented on potential limitations of Occam's razor in biology. He advances the argument that because biological systems are the products of (an ongoing) natural selection, the mechanisms are not necessarily optimal in an obvious sense. He cautions: "While Ockham's razor is a useful tool in the physical sciences, it can be a very dangerous implement in biology. It is thus very rash to use simplicity and elegance as a guide in biological research." In biogeography,