The new study built in 1877 now holds Charles Darwin's writing desk, chair and numerous objects connected with his work.
Darwin had the old study where The Origin was written converted into a smoking room.
Charles Darwin's home and neighbourhood at Downe, in Bromley, are being proposed as a World Heritage Site.
The Department of Culture, Media and Sport has put forward 'Darwin at Downe' as the UK's World Heritage Site nomination bid for 2006.
If the UNESCO World Heritage Committee inscribes the site in summer 2007, 'Darwin at Downe' will join the 26 other UK World Heritage sites, including the City of Bath, the Tower of London, Kew Gardens and Stonehenge, as well as international sites such as The Great Barrier Reef, the Pyramids of Giza and the Great Wall of China.