Once the shy academic in the rambling house on the edge of the village published his big book, the flood gates opened: there are accounts of the Downe village postman staggering under the sacks of mail he carried every day to the home of Charles Darwin.
In June 1873 the postman was bringing something special: a gift – on public display for the first time this week – from a fellow author of a book arguably as infamous and influential as On The Origin of Species. The copy of Das Kapital, Kritik der Politischen Oekonomie, was inscribed to Darwin from "his sincere admirer, Karl Marx".
It took Darwin over three months to compose a suitable response. He finally wrote in October: "Though our studies have been so different I believe that we both earnestly desire the extension of knowledge and that this in the long run is sure to add to the happiness of mankind."
The book in its original paper cover, on loan from a Darwin descendant, is part of a £1m exhibition which English Heritage has created at the scientist's home to celebrate the bicentenary this Thursday of his birth, and the 150th anniversary of publication of his theory of natural selection.
Sharp-eyed visitors may spot what Darwin didn't admit to Marx. The ivory paper knife which he used to cut the pages of new books is also on display: the uncut pages prove conclusively that he got less than a third of the way through Das Kapital.
There is an old story that Marx wished to dedicate Das Kapital to Darwin, but it turns out to be a myth. Edward Aveling wished to dedicate his The Students' Darwin and was declined by Darwin. The details are provided by "The Friends of Charles Darwin" here.