The original draft of Charles Darwin's On the Origin of Species was published online Thursday for the first time, joining thousands of the influential scientist's papers, photographs and other documents.

About 20,000 items contained in around 90,000 electronic images — a "treasure trove" of material — were published Thursday on the Darwin Online website, according to the Cambridge University Library, which holds all of Darwin's papers.

"This release makes his private papers, mountains of notes, experiments and research behind his world-changing publications available to the world for free," said John van Wyhe, the director of The Complete Work of Charles Darwin Online project, or Darwin Online.

The collection, which van Wyhe described as a "treasure trove," includes his notes from the five-year voyage of the HMS Beagle, where he collected fossil and specimen samples and first began to formulate his theory of evolution. The documents also include the first draft of his seminal Origin of Species from the 1840s and even recipes from his wife Emma's recipe book.

Darwin's On the Origin of Species, published in 1859, remains one of history's most influential and talked about scientific papers. It introduced the theory that populations evolve over the course of generations through a process of natural selection, a theory that became the backbone of modern biology.