 Evolution in its contemporary meaning in biology typically refers to the changes in the proportions of biological types in a population over time (see the entries on  evolutionary thought before Darwin and  Darwin: from Origin of Species to Descent of Man  for earlier meanings). As evolution is too large of a topic to address thoroughly in one entry, the primary goal of this entry is to serve as a broad overview of contemporary issues in evolution with links to other entries where more in-depth discussion can be found. The entry begins with a brief survey of definitions of evolution, followed by a discussion of the different modes of evolution and related philosophical issues, and ends with a summary of other topics in the philosophy of evolution focusing particularly on topics covered in this encyclopedia.