Fascinated by the diversity of living organisms, humans have always been curious about its origin. Darwin was the first to provide the scholary and persuasive thesis for gradual evolution and speciation under natural selection. Although we now have much information on evolution, we still don't understand it in detail. Many questions still remain open due to the complexity and multiplicity of interacting factors. Several approaches mainly arising from population ecology and genetics are presented in this book in order to help understand genetic variation and evolution.