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Somewhere out there was a turtle and a mockingbird that changed human understanding of how life on Earth evolved.

The Galapagos Islands are unique, thanks to their isolation from the mainland, proximity to the Equator, competing ocean currents, and volcanic composition. As a result they’re both tropical and temperate, with a delightfully weird variety of flora and fauna. (All of which arrived from somewhere else after the islands formed millions of years ago, by swimming, floating, flying, or otherwise hitchin’ a ride. Today, most of these species are endemic.)

But on this day in 1835, we didn’t know any of that. Ecuador had just claimed the archipelago, and colonization was on the horizon. Whaling and sealing—which would soon decimate island species—were in full swing. Giant tortoises were plentiful. And a 26-year-old naturalist named Charles Darwin arrived aboard the British Royal Navy ship HMS Beagle, which had sailed from England nearly four years earlier on a mission to chart South America.

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Darwin wrote to his sister that he expected the geology and zoology of the islands to be interesting. He hoped to discover species new to science. At the time, most people believed in the independent creation of species, so he didn’t expect to discover species that were similar but distinct from island to island—while also resembling those he’d seen on the South American mainland.

Fun Fact

The crew took small tortoises aboard the ship to keep as pets.

Darwin took pages of notes on the landscape and its flora and fauna, including mockingbirds, tortoises, finches, and swimming iguanas. He also collected specimens—“every plant which I could see in flower,” he later wrote—plus insects and animals, including a tame mockingbird that bore such similarity to ones in Chile and Peru that it raised questions for him about species distribution. He also learned that shells of tortoises varied between the islands.

(TL;DR: The guy caught a lot of birds.)

The specimens and observations he collected tugged at him for the next few years. The result would turn up more than 20 years later as On the Origin of Species, Darwin’s seminal work explaining the theory of evolution through natural selection.

He showed how species could remain similar while developing adaptations for their particular environments. In doing so, he put the Galapagos Islands on the map—and gave the world a new way of understanding how life adapts.

By the Numbers
  • 5 weeks: Time Darwin spent in the Galapagos
  • 13: Major islands in the Galapagos chain
  • 97 percent: Reptiles and land animals in the Galapagos found nowhere else on Earth
Also on This Day
  • 1514: Cardinal Thomas Wolsey becomes archbishop of York
  • 1821: Central American countries, including Costa Rica, Guatemala, Nicaragua, gain their independence from Spain (more on Latin American independence tomorrow!)
  • 1952: Per the UN, British rule ends in Eritrea