As early as last summer, before the Darwin commemoration caravan really got rolling, it was clear that this year was going to be one of the busiest ever for tourism in the Galapagos Islands. Visitor numbers, which rose from 40,000 in 1990 to more than 140,000 in 2006, are expected to reach 180,000.

The human population has risen similarly over the past 20 years, nearly fourfold, to 30,000. Many recent arrivals have been working illegally, and the Ecuadorean government has recently begun sending them back to the mainland.

Fruit flies have been carried on to two islands, threatening indigenous crops, a parasite has been discovered in penguins and Unesco has listed the Galapagos as one of the World Heritage sites it regards as endangered. Yet the islands are still recognisably the living laboratory that inspired Darwin, which is why so many want to visit them.

Andrew Marr is not saying that tourism should stop but that it “should be limited in some way” and “more high-end”. Tour operators would argue that it already is. The average cost of a seven-night cruise – excluding international flights and a stopover in Quito – is £2,500. Most boats take between 10 and 50 people and the biggest, with a capacity of 90, usually has half that number. The number of visitors per day on an island is restricted, tourists are guided at all times, kept to paths, warned to maintain their distance from animals and even told, while on their boat, to use biodegradable sun factor and shampoo.

Some visitors, though, returning after an interval of years, have been struck by both the weight of numbers of their fellow tourists and by wildlife that seems “tamer”. Mark Cawardine, writing in the travel magazine Wanderlust after his second visit, reported seeing a lone albatross on her nest surrounded by three tour groups – 48 people in all.

The Ecuadorean government is said to be considering raising the Galapagos National Park fee, paid by every tourist, from $100 to $135. Some tour operators believe it should be much higher. “In most Kenyan parks it’s $70 a day, nearly $500 a week,” said one. “That’s what it should be in the Galapagos, and they should spend it on education, jobs and conservation policing.” Some tour operators would also accept further limits on tourist numbers.

Andrew Marr says that, for him, the islands really were a once-in a lifetime experience; he has had his treat and won’t go again. If your environmental concerns outweigh your curiosity, perhaps you shouldn’t go at all.

Instead, try the Falkland Islands, where Darwin himself spent much time. Here you will see five different species of penguins, 20-foot-long elephant seals belching on the beaches, killer whales patrolling the shore – and colonies of albatrosses watched by tourist groups that will be closer in size to four than 40.