Things get improved because in their current form, they do not work properly. Henry Petroski's book, The Evolution of Useful Things, traces the development of objects in our everyday life, including detailed histories of the development of the staple, the zipper, silverware, and hand tools. The book is interesting, although Petroski does tend to shy away from offering a theory of development, and instead offers a conjectures about how things might have developed. He explains, but he does not offer a theory or an argument that explains everything. Overall, though, a goos book, well researched, well illustrated, and interesting on many levels.