Sometimes it is equated with the Modern synthesis, which is not strictly speaking correct as it was a fusion between the ideas contained in the Origin of species (1859) and the mechanisms of heredity discovered by Gregor Mendel (1822-1894). However, by the turn of the 20th century, neo-Darwinism has become part of a three-way split between Mendelians, mutationists and selectionists. It was the Modern synthesis that brought together these different strands into one overarching theory.
See Darwinism, Hereditary, Heritability, Mendelian genetics, Modern synthesis, Mutation (biology), Natural selection, Recapitulation theory (or biogenetic law), Theory of natural selection