An "extremely rare" manuscript signed by English naturalist Charles Darwin is expected to fetch up to $790,000 at a Sotheby's auction next month.

The document contains a passage from the famous 1859 work On the Origin of Species, in which Darwin put forth his theory of evolution by natural selection.

The document was once thought to be a discarded page from an earlier manuscript of the work. But experts now understand the manuscript was written in 1865 and sent to Hermann Kindt, the editor of the Autographic Mirror who had requested a signed writing sample from Darwin.

"While some of Darwin's notes and manuscript leaves have survived over the last hundred or more years, he was known to obsessively revise his publications, often discarding pages from working drafts and treating them as scrap paper, making any autograph manuscript extremely rare," Sotheby's said in a statement.

On the Origin of Species was voted the most influential academic book of all time in a public poll held during Academic Book Week in 2015, beating out other seminal works including The Communist Manifesto by Karl Marx and Friedrich Engels, The Republic by Plato, and the complete works of William Shakespeare.

The book offers Darwin's revolutionary idea that species evolve incrementally over generations via the process of natural selection.

"I have now recapitulated the chief facts and considerations which have thoroughly convinced me that species have been modified, during a long course of descent, by the preservation or the natural selection of many successive slight favorable variations," the document reads.

Darwin backed up his theory with evidence collected during his 1831-1836 voyage on the HMS Beagle, during which he observed and collected specimens from a number of species. One major observation occurred on the Galapagos Islands off the coast of Ecuador. Darwin noted that the finches on the island were similar to finches on the mainland, however, the availability of different foods in each area had led to discrepancies in beak anatomy.

"I cannot believe that a false theory would explain, as it seems to me that the theory of natural selection does explain, the several large classes of facts above specified," the excerpt adds. "It is no valid objection that science as yet throws no light on the far higher problem of the essence or origin of life."

The manuscript will be placed on display at Sotheby's in New York between Nov 30 and Dec 8, and online bids will be accepted between Nov 25 and Dec 8. The auction house estimates that the document will fetch between $600,000 and $790,000.

The auction, which is titled Age of Wonder, will also include a first edition of On the Origin of Species and a copy of On the Tendency of Species to form Varieties, which is a scientific paper written by Darwin and Welsh naturalist Alfred Russel Wallace.