After two centuries of intensive scientific effort, we now have the luxury of a theory that provides a general explanation for that richness, often in quite considerable detail. That theory is Darwin's theory of evolution by natural selection. Darwin's theory is famous for two reasons. One is that it is the second most successful theory in the history of science (after quantum theory in physics) in terms of its ability both to explain what we see in the natural world and to stimulate new ideas and research that have uncovered rich seams of novel findings. The second has been its ability, as a theory, to provide a unifying framework for a disparate array of disciplines that do not always see themselves as natural allies. That array includes not just the various life sciences (ecology, genetics, anatomy, physiology, biochemistry and animal behaviour), but also "hard" sciences like chemistry, the softer sciences like medicine, sociology, anthropology and economics, and even the humanities. History, linguistics, literature - all fall under the purview of evolutionary theory"--