Simplify the following text for a Grade 15 native English-speaking person.
Original: His most important theoretical book was : `` Das Werden der Organismen , eine Widerlegung der Darwinschen Zufallslehre '' ( Jena , 1916 ) ( translation : `` The Origin of Organisms - a Refutation of Darwin 's Theory of Chance '' ) .
Simplified: He wrote : Das Werden der Organismen , eine Widerlegung der Darwinschen Zufallslehre ( Jena , 1916 ) ( translation : `` The Origin of Organisms : a refutation of Darwin 's theory of chance '' ) .