Humans didn’t find out about the Galapagos Islands in 1535, and even then, the discovery was accidental. While sailing to Panama from Peru, Dominican friar Fray Tomas de Berlanga found his ship set off course by the prevailing currents. He was the first person to document his arrival at the Galapagos Islands, where he was welcomed by giant tortoises – the likes of which he had never seen before. Berlanga wrote in his recounts that they were “such big tortoises that each could carry a man on top of himself.”
How did these land-dwelling reptiles – which spend up to sixteen hours a day resting – end up on a remote archipelago, 600 miles away from the closest mainland shore? Given this context, it’s truly a wonder to observe the diverse ecosystems which the Galapagos Islands are known to support today. They’re home not only to giant tortoises, but other endemic species such as marine iguanas, seals, and sea lions as well. Here’s what scientists think about the origin of the region’s remarkable wildlife.
Carried by the currents
Much like the first humans, it’s believed that some of the Galapagos Islands’ most renowned creatures were brought over by the ocean currents. The only difference is that they might have arrived as long as three million years ago.
This has given the animals sufficient time to evolve into entirely new species, which aren’t found anywhere else in the world. Observing this phenomenon – how animals developed features to adapt to life in the Galapagos Islands – helped inspire Charles Darwin’s theory of evolution.
Take Galapagos giant tortoises, for example. Their closest living relatives are the Chaco tortoises which live in Argentina, Paraguay, and Bolivia. On average, Chaco tortoises measure between six to ten inches in length. On the other hand, Galapagos tortoises can grow up to lengths of six feet (72 inches).
Scientists believe that when tortoises first got swept away by the currents, it’s more likely that the larger members would survive the long journey to the Galapagos Islands. They would be able to hold their heads higher above the water, and survive for longer without food, thanks to their fat reserves.
Even upon arriving, size would prove to be an advantage for the tortoises. Given the scarcity of food in the region, they would have to go long durations without a meal. Today, Galapagos tortoises have evolved to survive for up to a year without any food or water.
Galapagos’ land and marine iguanas – or rather, their evolutionary ancestors – are said to have made the long oceanic journey as well, albeit not all at once. It is believed that the iguanas island-hopped from South America to the Galapagos, using floating vegetation as their makeshift rafts.
After their arrival, the iguanas evolved – over the course of eight to ten million years – into the two different species of land and marine iguanas which exist today. It is believed that marine iguanas used to inhabit those islands in the Galapagos archipelago which are now submerged. Due to their reliance on water-based food sources such as algae, they developed useful features such as flattened tails which allow them to swim better.
Disproven theory: the giant land bridge
Although it is widely accepted today that the Galapagos Islands’ reptiles and mammals arrived via the ocean, this wasn’t always the case.
Back in the late-1800s and early 1900s, scientists hadn’t been able to prove that land-based animals could cross an ocean and live to tell the tale. Some believed that the Galapagos Islands’ giant tortoises had been brought over by sailors.
Others, such as German paleontologist Georg Baur, theorized that the Galapagos Islands were the remnants of a larger landmass which used to be connected to South America in the past. Baur believed that the native species made the journey to the archipelago by land and were left stranded once the surroundings submerged.
Naturalist William Beebe was one of the scientists who tried testing the ocean-crossing theory. He threw a tortoise off a yacht in an attempt to gauge the animal’s swimming abilities. Although the tortoise got off to a strong start, it wasn’t able to survive for longer than a week – not nearly long enough to travel from the South American mainland to the Galapagos Islands.
It would take another century before this theory came to be accepted. In the 1950s, research on plate tectonics confirmed that the Galapagos Islands were formed as a result of volcanic activity. This confirmed that the archipelago never used to be connected to South America by land.
Then, in 2004, an Asian Giant Tortoise – which is only found in countries in South Asia – was found walking on a shore in Tanzania, Africa. The tortoise would have had to swim around 750 kilometers to get there. This served as proof that it wasn’t impossible for giant tortoises and the rest of the Galapagos Islands’ terrestrial creatures to have made their way across the Pacific Ocean.