In a frock coat with sideburns pasted to his jowls, he poses at Darwin's microscope for TV programme, Blue Peter. "At last, my broad forehead comes into its own, " he says. "But I haven't had whiskers like these since the Seventies."
"Jolly good likeness," says Stephen Keynes, Darwin's great-great grandson, who is setting up an international educational charity for natural history on the estate. His advice to English Heritage was to keep the house shabby.
The timing of opening the house, on Good Friday, is brilliant. Darwin is back in fashion, with BBC2 running a week of programmes about him. "Science is sexy again," says Down House manager, Tracy Thursfield. "It's millennia fever."
At the house, Darwin produced 17 books, numerous scientific papers, and 10 children, seven of whom survived until adulthood. He and his wife, Emma, spent 40 years there, adding wings to the old parsonage, until it had 16 bedrooms and a giddying roof line.
The house was taken over by the Royal College of Physicians in 1927 and maintained as a museum to Darwin, but dry rot and woodworm began to get the better of the fabric of the house. The roof needed attention. So, in 1996, English Heritage acquired Down House through a donation from the Wellcome Trust and spent pounds 2.2m of lottery money on its restoration.
This was the first time English Heritage had restored a house without particular architectural significance, or period rooms that would pass the style trial. It used old photos and paintings to rebuild the five period rooms downstairs - the hall, billiard room, dining room and drawing room, and Darwin's study. Through paste and papers, wall-to-wall Axminster carpets and meticulous props, it has brought the family man and scientist to life. The challenge was to build around a celebrity the sort of house that Hello! would photograph if the Darwins were still alive.
Each room illustrates a different aspect of Darwin's personality, while remaining true to the original decor. In the biliously coloured billiard room are portraits of the playful Darwin, whose father cautioned: "You care for nothing but shooting, dogs and rat-catching and you will be a disgrace to yourself and all your family." On a patriarchal picture, taken late in life by Julia Margaret Cameron, he writes: "I like this photograph very much better than any other which has been taken of me."
The austere and dignified dining room shows his Anglican, Tory, establishment background, with late Regency mahogany furniture, family portraits of the Wedgwoods (his wife's family) and the Darwins, and his bust in marble on a plinth. A steamer chair by the bay window reveals his nostalgia for the five years he spent on HMS Beagle. So does his ship-shape study, in which Darwin labelled everything, including his slide rule by the pigeon bones. On his correspondence table lie log books, journals and post from scientific sleuths all over the world.
That dialogue continues after his death. This summer, a scientist from the Smithsonian Institute in the US, who discovered a blood stain in one of Darwin's books, will take a DNA sample to reveal whether Darwin really caught Chagas fever from a South American beetle. The sweatband from Darwin's top hat was rejected as unsuitable for this piece of forensic science. Whatever his ailment, Darwin was a chronic hypochondriac, as the spittoons, inhalers, knitted shawls and daily medical records reveal.
Darwin as a family man is depicted best in the drawing room. Standing on the piano are garden pots full of worms. Darwin's children would play the bassoon and piano to them while their father observed the effect of music on worms turning. Unlike most Victorian households, children were seen and heard here. His wife Emma's interest in natural history spills over into the decoration, with it cow parsley, wheat sheaves, poppies and butterflies - and that's just the curtains.
Clearly, the Darwins had execrable taste. A profusion of pattern and riot of colour set raspberry and cobalt blue, pea-green and magenta against each other in the same room. Worse, Darwin and his wife did not buy Arts and Crafts wallpapers and fabrics, but the cheaper high-street equivalent, which English Heritage had a hard job matching.
Working with classic English paint, paper, fabric, lino and Axminster carpet manufacturers, Mr Bryant researched the products available at the time. Then he sourced them from suppliers' archives, cross-matching colours and patterns like a true scientist. The task of decorating the rooms again was made harder by the Darwins' indifference to Art and Fashion. As Gwen Raverat wrote of her relatives in Period Piece: "When they bought an armchair, they thought first of whether it would be comfortable, and next of whether it would wear well. Then, a long way afterwards, whether they themselves happened to like the look of it. The result, though often dull and sometimes unfortunate, was on the whole pleasing because it was, at any rate, unpretentious."
Mr Bryant was undaunted. He saw his task as drawing a portrait of Darwin in everyday household things. "Their taste was a slight problem for me." he admits, but the only time he lost his nerve was in the drawing room, where he couldn't bring himself to have the cornices painted mauve and gold. So, they are magnolia.
Seven bedrooms upstairs have been turned into exhibition rooms to tell the story of a conventional Victorian who shocked the world. They show that his scientific knowledge got off to a slow start: the dunce at school, fossil collecting at Cambridge, years on the Beagle meticulously collecting flora and fauna from forays into South America. The Natural History museum has lent some stuffed animals, including a puffer fish, pangolins, a giant white fulmar spreading its wings, and a Galapagos turtle. No apes. In a clamorous room tapes of actors playing indignant bishops and politicians reviling On the Origin of Species takes us up to date with genetics, and the cloning of Dolly the sheep.
If visiting scientists complain that there isn't enough to inform the Cambridge undergrad here, Mr Bryant will tell them he didn't do up the house for them. Rather, it is to be a popular learning centre for the young. Nor did he reconstruct it for the style police, who want to know why there aren't piles of papers next to an unplumped chair. He dismisses this as "the chimpanzee approach to conservation", from which I presume he despises artificiality and, in particular, unnatural selection. Darwin would approve.
Down House, Luxted Road, Downe, near Bromley, Kent. Entry by timed ticket only, pre-booked one day in advance, call 0870 6030145