An inherent characteristic of humans is the tendency to group together objects or beings that have similar characteristics. Primitive man, for example, already distributed living things into two groups: edible and inedible. The distribution of objects or beings into groups according to their similarities and differences is what is called classification.
From 1900 until about 1920, adherents of Mendelian genetics believed that only mutations were responsible for evolution and that natural selection was not important in this process. After that several scientists began to reconcile the ideas of natural selection with the facts of genetics, which culminated in the formulation of the synthetic theory of evolution, sometimes also called neodarwinism.