Evolution
IN THE NATURAL WORLD, like only breeds with like. A group of things that can breed together is known as a species. Until the 17th century it was thought that each species had been individual designed and created for a particular purpose, but new knowledge threw doubt on this idea. Geological evidence showed that the Earth was older than was once thought. Fossils showed that many forms of life had vanished and that species seemed to change, or over time. In the 19th century two British naturalists, Charles Darwi (1809-1882) and Alfred Russel Wallace (1823-1913), proposed a cause this evolution - the weeding out of inherited variations, favoring members of a species at the expense of others. This process of "Natural selection" forms a key part of modern biology