What Lives on the Galápagos Islands: The Animals of the "Laboratory of Evolution" and How the Islands Formed

In September 1835, the British naval vessel HMS Beagle dropped anchor at San Cristóbal Island, at the eastern edge of the archipelago. On board was a young Charles Darwin, who is said to have conceived the idea of evolution here.

According to the video, the prevailing view in the West at the time was that living things had been individually created from the start to suit the conditions of their particular lands, and that species were fixed. But the Galápagos Islands are relatively young islands formed by volcanic activity, which means every creature living there must have arrived later. Darwin would later point out that even similar organisms looked slightly different from one island to the next.

The video stresses, however, that Darwin did not suddenly realize "living things change" while he was on the islands. His work centered on collecting specimens, not building theories. Even so, aboard the ship as it left the islands and continued its voyage, Darwin wrote that "the assumption that species do not change may be shaken." It would be more than 20 years before he put forward his theory of evolution in On the Origin of Species.

Darwin's finches are a group of small birds living on the Galápagos Islands, and their appearance varies slightly from island to island. The most striking difference is the shape of the beak: some are thick and short, some long and slender, some sharply pointed. These differences correspond mainly to each island's environment and the food it provides. In an environment with a particular food source, individuals that can eat it efficiently are more likely to leave offspring, and among the next generation, which inherits those traits, even better-suited individuals survive. The video explains that this fits the mechanism of evolution very well.

On the other hand, Darwin himself apparently did not pay much attention to these birds, and it is known that he did not label his specimens by island. The finches only became linked to evolution after his return to England, following the classification of the specimens by ornithologist John Gould and Darwin's own reexamination. Still, the video says it would be a little harsh to blame Darwin, because the species differ greatly in diet and vary widely in both appearance and habits.

As examples of that diversity, the woodpecker finch holds a cactus spine in its beak to pry insects out of holes in trees. There is also a blood-drinking bird called the vampire finch, which perches on the backs of boobies, pecks at the base of their feathers, and sips their blood. It does not drink blood year-round, though: from January to early June, when food is plentiful, it eats seeds and insects like other finches, and relies on blood only from June to November, during the dry season. Its gut is rich in the same bacteria found in vampire bats, which are also known for drinking blood, and these are thought to help process the large amounts of sodium and iron contained in blood.

The video presents Darwin's finches as a textbook case of "adaptive radiation." Adaptive radiation is the phenomenon in which a common ancestor adapts to a variety of environments and splits, in a short period, into new species with diverse traits. On a vast continent, the roles of cracking hard seeds, digging out insects, and even drinking blood are already filled by other organisms. But on these islands, there was no one to fill them.

The video introduces two events to show that this process has continued in recent times.

In 1977, a severe drought struck Daphne Major. The small, soft seeds were eaten up, and only large seeds with hard shells remained. In just over two years, the island's medium ground finches fell from about 1,400 to a few hundred. Nearly all the survivors were individuals with large, thick beaks capable of cracking the hard shells, and when the generation born the following year was examined, average beak depth had increased by about 0.4 mm. The video says this meant the phenomenon of natural selection had been measured not in fossils but in the bodies of living birds, and within a single year.

In 1981, a single male flew to Daphne Major from Española Island, more than 100 km away. This bird mated with a female on the island, and their offspring had a distinctive song and a distinctive beak, so they stopped interbreeding with any of the three other species on the island. The video describes this as "humanity may have witnessed the birth of a new species." This lineage, which researchers call "Big Bird," still lives on the island today.

There are four species of mockingbird on the Galápagos Islands, and the most widespread is the Galápagos mockingbird. It is about 25 cm long, with a black band around its eyes and a thin, downward-curving beak. It is omnivorous with a broad diet: it walks around on the ground catching centipedes and lizards, but it is also fond of fruit, which makes up about a third of its diet. Because the seeds in its droppings sprout, it also serves to disperse plants. It has also been observed breaking open the eggs of red-footed boobies and large birds to eat the contents, picking food scraps from the teeth of sleeping sea lions, and pecking parasites and skin off land iguanas.

According to the video, what led Darwin, after he left the islands, to the idea that "species may change" is thought to have been not the finches but this mockingbird. Darwin, who had not labeled his finches, did label his mockingbirds. That is why he was able to notice that birds with different appearances turned up each time he moved to another island.

One characteristic of this bird is "cooperative breeding," in which grown offspring stay with their parents and help raise their younger siblings. The helpers are mostly sons, so the one bringing food to next year's chicks is an older brother from the same nest. In the islands' wildly fluctuating climate, this is thought to be a strategy for a family to defend a single territory.

The Galápagos giant tortoise is the largest living species of land tortoise in the world, with a shell length of over 1.3 m, a weight of 300 kg, and a lifespan of more than 100 years. This tortoise is also one of the creatures that contributed to the birth of the theory of evolution: on Floreana Island, Darwin heard from the vice-governor he met there that "you can tell which island a tortoise comes from by looking at its shell."

Their ancestors are thought to have drifted from South America about 2 to 3 million years ago. Tortoises cannot swim but can float, and the video speculates that individuals swept out to sea by storms rode the currents to the archipelago. Today's shells fall into two broad types: tortoises on high, humid islands have dome-shaped shells like an upturned bowl, while those on dry, low-lying islands have saddle-shaped shells that flare upward around the neck. Saddleback tortoises can stretch their necks far, allowing them to reach the pads of prickly pear cacti that grow in arid areas. Individuals able to reach high are thought to have survived more readily, spreading that trait.

However, a giant tortoise can survive for nearly a year in a ship's hold without food or water. For whalers and pirate ships, there was no more convenient food source: loaded aboard alive, they provided meat that would not spoil until the end of the voyage. More than 100,000 were taken over the course of the 19th century, and of the roughly 15 species thought to have once existed, 11 survive today.

The video also offers hope. The Española Island species had dwindled to just 14 animals in the wild: 12 females and 2 males. A breeding program was launched from there, including efforts such as bringing animals over from the San Diego Zoo to breed them, and the island's tortoises recovered to more than 2,000. The program completed its mission in January 2020, and in June, the 15 parent tortoises that had contributed to breeding were returned to their home island.

The marine iguana is the only lizard in the world that dives into the sea to feed. It grows up to 1.5 m long and is black, the same color as lava. Its snout is short and flat, suited to scraping algae off rocks. Its sharp claws let it grip the lava so it isn't swept away by waves, and it swings its tail side to side to move through the water.

Darwin, too, apparently found its appearance bizarre. He wrote in his diary that "large, most disgusting, clumsy lizards" prowled the black lava rocks, and went on to note that someone called them "imps of darkness." Another person recorded that they were so unsightly that no one on the ship would eat them. The video points out that, ironically, this "unappetizing" quality may have protected them from overexploitation.

Their black bodies are thought to be an adaptation to life at sea. They are reptiles that originally lived on land, and as cold-blooded animals they quickly lose body heat in the ocean, so they reportedly developed black bodies that absorb sunlight easily, allowing them to warm up quickly when they come ashore. They also occasionally blow a white mist from their heads as if sneezing. This is excess salt, swallowed along with seawater, that has been concentrated by glands deep in the nose and expelled; the accumulated salt sometimes forms something like a white crown on their heads.

Their most astonishing ability is shrinking their bodies. When an El Niño event raises sea temperatures, the green and red algae they prefer are replaced by hard-to-digest brown algae, and their food disappears. During such periods, the same adult individuals were reported to have shrunk by up to 20% over two years, or about 6.8 cm in snout-to-vent length. And this happened not just once or twice. Normally, a vertebrate's body length only ever increases, but these iguanas are thought to have made themselves smaller by reabsorbing not only soft tissue but even bone. A smaller body needs less energy, and a smaller mouth can scrape the scant remaining algae more efficiently. Data show that individuals that shrank by 2.1 cm or more lived nearly three years longer on average, and when food returns they grow back to their original size. Individuals that could not shrink died off in famine years, while those that could left offspring, and this accumulation is thought to have established the ability in the population. The video says that in places where the environment swings violently on a cycle of a few years, a body that can change may be more advantageous than a fixed one.

The Galápagos land iguana is a close relative of the marine iguana, descended from those that stayed on land rather than heading to sea. It grows to over 1 m long and is yellow to orange in color. It digs burrows in the ground for nests and lives about 50 to 60 years. With a tough oral lining and a sturdy digestive tract, it can eat its staple food, prickly pear cactus, whole without removing the spines. It also gets most of the water it needs from cacti, so it can survive even in lowlands where it almost never rains.

Its ties to its marine cousin have not been completely severed, however. On South Plaza Island there are hybrids whose fathers are marine iguanas and whose mothers are land iguanas. This is a cross between animals of different genera, an extremely rare case among reptiles; it was discovered in 1981 and confirmed by genetic analysis in 1997. Having inherited a body built for life on land from its mother and sharp, rock-gripping claws from its father, this hybrid can climb prickly pear cacti to feed—something neither parent can do. However, only about 20 had been confirmed as of 2003, and they are thought to be unable to produce a next generation, making them a one-generation existence.

Penguins on the equator may sound like a joke, but it is true, the video says. The Galápagos penguin is about 50 cm long and weighs 2.6 kg or less, and the video describes it as the smallest of the penguins. Because the northern part of Isabela Island lies north of the equator, it is also the only penguin in the world that breeds in the Northern Hemisphere.

The reason penguins live in the tropics lies in the ocean currents. On the western side of the archipelago, the eastward-flowing Equatorial Undercurrent collides with the slope of the seafloor, and the cold, nutrient-rich water, with nowhere else to go, is pushed up to the surface. As a result, plankton blooms in huge quantities even on the equator, drawing small fish to feed on it. That is reportedly why more than 95% of Galápagos penguins are concentrated on the western coasts of Fernandina and Isabela islands.

To adapt to the heat, their bodies became smaller. For a given shape, as a body gets smaller, its surface area shrinks less than its volume does, so the ratio of surface area to volume increases. Since heat production tends to depend on volume and heat loss on surface area, a small body is better suited for penguins—originally cold-climate animals—to live in the tropics. That is the explanation the video gives.

Even so, the equatorial sun is harsh, and with no soft soil to dig burrows in, they nest in lava crevices and caves. During the day, they spread their wings to shade their feet and open their mouths to release heat, and if they are still too hot, they go into the sea. Almost all of their behavior is devoted to keeping their body temperature from rising too high.

And the currents that have sustained them sometimes drive them to the brink. When El Niño raises sea temperatures, the nutrient-supplying current weakens and their food disappears. About 77% were lost in 1982–1983, and about 65% in 1997–1998. The current estimated population is about 1,200, and the species is listed as endangered. In recent years, researchers have also been installing artificial nest burrows in the lava, and it has been found that simply providing shade changes breeding success rates.

Of the roughly 40 cormorant species in the world, only one—the flightless cormorant—cannot fly. Its body is among the largest of any cormorant, with some reaching 5 kg, yet its wings are shorter than those of any other cormorant, clearly deviating from the general rule relating wing size to body weight. Its breastbone makes this even clearer: the keel, the ridge that anchors the flight muscles, has almost entirely disappeared. In other words, it discarded not just its wings but the very foundation for flying. With no predators on land, all its food on the seafloor right beneath it, and the cost of maintaining the ability, losing flight makes sense, the video says.

Its breeding is also unusual. Once the chicks have grown to a certain point, the female leaves the nest, pairs with another male, and lays eggs again, while the male left behind raises the young on his own. This breeding system is called "sequential polyandry," and this is reportedly the only cormorant species that has it. In courtship, too, the roles are reversed compared with typical birds: females take the lead in courting and compete aggressively over males. In years when food is plentiful, a female can breed up to three times a year, which makes males the object of competition.

The blue-footed booby's blue feet are produced by both structure and pigment. The blue tint comes from the arrangement of collagen, while the vividness is determined by carotenoids, pigments taken in from the fish it eats. Because carotenoids are also used in immune function, the blueness of the feet signals outwardly how well the bird is currently eating and how healthy it is. In fact, it has been reported that when males were deprived of food for 48 hours, their foot color clearly dulled, and when they were given fresh fish again it returned within about 24 hours. Furthermore, when a male's foot color was artificially dulled at the point when the female laid her first egg, the second egg she laid was noticeably smaller. The female was deciding how much to invest in this breeding attempt by looking at her partner's feet.

Blue-footed boobies do not build nests; they lay eggs directly on the ground and outline the area around them in white with their own droppings, marking the boundary of their territory. They usually lay two eggs, but because these hatch 4 to 5 days apart, the first chick grows larger, and in years when food is scarce the older chick apparently sometimes pushes the younger one out of the nest. And their numbers are now declining. According to a survey published in 2014, the estimated population as of 2012 was 6,423, less than a third of what it was in the 1960s, and only 134 chicks fledged during the survey period. The leading suspected cause is a sharp decline in sardines, their staple food.

The red-footed booby is the smallest of the boobies, about 70 cm long. Its feet are bright red, and its beak shades from pale blue to pink. Its most distinctive trait is that it is the only booby that nests in trees rather than on the ground. It has webbed feet yet long toes, with claws that can grip branches firmly—an unusual build for a seabird—and nesting in trees is thought to help it evade predators. It feeds on flying fish and squid offshore and prefers the dim hours of dawn and dusk. Its estimated population in the archipelago is about 30,000, many of them gathered on Genovesa Island at the northern end. Interestingly, when vampire finches drink its blood, it barely resists and stays still. It is speculated that the relationship may once have been one in which the finches removed parasites from its feathers.

The second half of the video introduces several islands and landforms while explaining how the archipelago formed.

Bartolomé Island, off the east coast of Santiago Island, is a small island of only about 1.2 km². Climb to its highest point, 114 m, and you can look down on Pinnacle Rock, a spear-like rock towering at the water's edge. Pinnacle Rock is said to be a remnant of an underwater eruption. When hot magma meets cold seawater, the water instantly flashes to steam and blasts the magma apart in what is called a phreatomagmatic eruption. The scattered volcanic fragments piled up and solidified, and over long ages the waves wore them away until only the hard core remained—or so it is thought. The slopes have almost no vegetation, only scattered plants that conserve water to the extreme, such as Tiquilia, with leaves covered in gray hairs. Even so, Galápagos penguins have been seen standing in the gaps between the rocks, and green sea turtles coming ashore on the beaches to lay eggs. The video describes it as a place where you can see, just as it is, the stage at which life takes its first steps on newborn land, and suggests that the newly formed Galápagos Islands may also have gone through such a scene.

Off the northeast of San Cristóbal Island rises a vertical wall about 148 m high. It is called León Dormido, Spanish for "sleeping lion," and in English, Kicker Rock, because it looks like a kicked-up shoe. It is actually a solidified volcano, and unlike Pinnacle Rock, the entire volcanic edifice is split in two; waves and wind eroded the weak parts to create a channel about 20 m wide. Because the wall continues vertically below the surface, when currents flowing at depth hit it, nutrient-rich water is pushed upward, plankton multiplies, small fish gather, and large fish gather in pursuit. In the narrow channel, you may see scalloped hammerheads, Galápagos sharks, green sea turtles, and schools of rays passing one another. Above the surface, too, blue-footed boobies, Nazca boobies, frigatebirds, and others nest on the rock ledges.

Rábida Island, south of Santiago Island, covers about 5 km². Its hallmark is a deep reddish-brown beach, and the reason is iron. The eruptions that built the island produced volcanic ejecta called scoria, and the lava was especially rich in iron. Iron exposed at the surface oxidizes on contact with the air. In other words, this island is slowly rusting—the same phenomenon that makes Mars red, the video explains. Behind the beach is a saltwater lagoon visited by American flamingos. Introduced goats and rats once pushed the island's plants to the brink, but the goats were removed, and the rats were eradicated by an elimination project that began in 2011. Today, on the red beach, which has regained its original ecosystem, you can see sea lions sleeping peacefully.

Isabela Island is the largest in the archipelago, with an area of about 4,600 to 4,700 km². This single island accounts for more than half of the archipelago's land area. It straddles the equator, with its northern part in the Northern Hemisphere and its southern part in the Southern Hemisphere. At its southeastern end is Sierra Negra volcano, 1,124 m high, whose summit opens into a huge caldera about 9.5 km east to west and about 7.5 km north to south; it is said to be one of the volcanoes that symbolize the archipelago's volcanic origins.

According to the video, the Galápagos Islands sit not on a plate boundary but directly above a hotspot, where hot rock rises from deep in the mantle. The hotspot barely moves, but the Nazca Plate on top of it moves about 5 cm per year toward the southeast. San Cristóbal and Española are islands 3 to 4 million years old, and erosion is already well advanced. Meanwhile, the youngest, Fernandina Island, formed only about 700,000 years ago. And the islands that exist today will eventually be carried east and sink.

The spotted eagle ray is a large ray with a black body densely covered in white spots; its width can approach 3 m, and its total length including the tail can reach 5 m. The tip of its head juts out like a duck's bill, and it has a venomous spine at the base of its tail. Despite its size, it is dexterous: crescent-shaped teeth line its upper and lower jaws in bands, and after digging up shellfish and crustaceans from the sand with its flat snout, it crushes them shell and all with these teeth. Then, using projections on the roof and floor of its mouth, it spits out only the shell fragments and swallows just the contents.

The Galápagos shark, despite its name, is not endemic; it reportedly got the name simply because it was described from specimens collected in the Galápagos. In reality, it is widely distributed in tropical to subtropical seas and prefers to gather around offshore islands and seamounts. It grows to about 3 m long, and like its close relatives it gives birth to live young rather than laying eggs; the pups, which receive nourishment from the mother through a placenta-like structure, are born at a length of several tens of centimeters. In the Galápagos, it reportedly sometimes attacks sea lion pups and marine iguanas coming out of the water.

The hammerhead shark's hammer-shaped head has eyes at both ends, and its nostrils are also set far apart. The meaning of this shape has long been debated. A commonly cited theory is that it gives them superior electrosensory ability, but in experiments comparing them with requiem sharks of similar size, there was no difference in their ability to detect electricity. The leading theories today are that spreading the electrosensory organs over a wide surface gives them a broad search area, and that the flat head allows them to turn at high speed. At Darwin and Wolf islands, hundreds of hammerheads can be seen schooling in a swirling mass. Why they congregate like this is unknown, but it is known that the adults that gather are not related to one another. The schools are not families but gatherings of complete strangers.

The whale shark is the largest living species of fish, reaching up to nearly 20 m long, with skin as thick as 10 cm in places. In the Galápagos, they are known to appear every year from July to December at Darwin Island at the northern end. Nearly all are females, and many have swollen bellies as if pregnant. Humans have almost never witnessed whale shark reproduction, so if they truly were pregnant, it would have been a major discovery. But closer investigation showed they were not pregnant, and why they come there is unknown. The reproduction of the world's largest fish remains a mystery, the video says.

The Sally Lightfoot crab is a crab commonly seen in the archipelago, with a shell about 8 cm wide and a vivid mottled pattern of red, orange, and yellow. It too is not endemic and is widely distributed along the coasts of the eastern Pacific, but in the Galápagos it has formed a symbiotic relationship with marine iguanas. Crabs have frequently been seen picking ticks off iguanas' bodies: the crab gets food, and the iguana gets rid of parasites. This is called "cleaning symbiosis" and is thought to benefit both sides.

At the end, the video sums up the archipelago as a whole. The new islands that emerged from submarine volcanic eruptions were places where living things had to start literally from zero. The only ones that made it were those that endured chance, by clinging to driftwood, being carried by the wind, or being transported by birds. They adapted to the peculiar environment of remote islands while also discarding what they no longer needed. In the modern era, this has in some respects led to fragility, as seen in the drastic declines in giant tortoise numbers and species caused by humans.

Still, hope remains, the video continues. In 1959, Ecuador designated 97% of the land area as a national park, and in 1978 the islands were inscribed as a UNESCO World Natural Heritage Site. The goats were removed, the rats eradicated, and the Española tortoises surpassed 2,000. The video concludes that the Galápagos Islands are called the "laboratory of evolution" not because answers are laid out there, but because it is a place where, just as Darwin did, someone is still asking questions today.