Simplify the following text for a Grade 12 native English-speaking person.
Original: The theory of recapitulation is often known as ontogeny recapitulates phylogeny .
Simplified: Haeckel formulated his theory as `` Ontogeny recapitulates phylogeny '' . The notion later became simply known as the recapitulation ( OED : ' a summing up or brief repetition ' ) theory .