Few voyages have had more impact on science than Charles Darwin's visit to the Galapagos Islands in 1835.
Chris Darwin with one of the islands' more famous animal inhabitants
It was, he wrote, "like giving to a blind man eyes - he is overwhelmed with what he sees and cannot justly comprehend it."
The archipelago of volcanic islands off Ecuador, with their unique diversity of plant and animal life, inspired Darwin's first ideas of evolution.
But what would he make of the islands today?
Despite efforts to protect one of the world's greatest natural history treasures, much has changed since HMS Beagle anchored at bays off the archipelago.
Charles Darwin's descendant Chris retraces part of the voyage for BBC Radio 4's It's My Story. He says the islands retain the sense of mystery and wonder that captivated his great, great grandfather.
"It's still got the innocence that really grabbed him 170 years ago," he told the BBC News website.
But he says the landscape would have looked very different then. The vast tracts of rainforest on the west coast of South America that Charles Darwin would have seen from HMS Beagle have been cleared, while wildlife on the islands has fallen prey to invasive species introduced by humans.
"There has definitely been damage in the sea," says Chris Darwin. "This is something I really noticed between the two trips I have taken. This time, I didn't see a single hammerhead shark and far fewer sea cucumbers."
The journey gave Chris Darwin, who was born in London but now lives in Australia, time to reflect on how his famous ancestry has shaped his life.
"I suppose I might describe myself as an amateur naturalist, or certainly a passionate naturalist," he tells the programme, "but I don't think I can claim to have many of Charles Darwin's genes because I failed my biology A level.
"Everybody was a bit worried because they didn't really mind me failing anything else but not biology. And I was doing badly and I got a tutor in for the summer holidays to teach me biology.
"And he introduced himself and I introduced myself and he said, 'You're Darwin,' he said. "'I can't teach you anything about biology', which I thought was really sweet. And then I went off and failed."
It's My Story: Beyond the Beagle is broadcast on BBC Radio 4 at 2000 BST on Thursday, and then available on the network's website for a short period afterwards.