The key concepts of Darwinian theory of evolution are

The key concepts of Darwinian theory of evolution are branching descent and natural selection.

Darwin proposed that species can change over time, that new species come from pre-existing species, and that all species share a common ancestor. In this model, each species has its own unique set of heritable (genetic) differences from the common ancestor, which have accumulated gradually over very long time periods. Repeated branching events, in which new species split off from a common ancestor, produce a multi-level "tree" that links all living organisms.