Simplify the following text for a Grade 16 native English-speaking person.
Original: Ernst Haeckel ( 1866 ) , in his endeavor to produce a synthesis of Darwin 's theory with Lamarckism and Naturphilosophie , proposed that `` ontogeny recapitulates phylogeny , '' that is , the development of the embryo of every species ( ontogeny ) fully repeats the evolutionary development of that species ( phylogeny ) , in Geoffroy 's linear model rather than Darwin 's idea of branching evolution .
Simplified: Ernst Haeckel ( 1866 ) proposed that `` ontogeny recapitulates phylogeny '' , that is , the development of the embryo of every species ( ontogeny ) repeats the evolutionary development of that species ( phylogeny ) .