Charles Darwin was 22 years old when he first peeled a banana. “Maukish & sweet with little flavor,” he noted in his journal from Santiago, the main island in the Cape Verde archipelago off the coast of West Africa. He preferred oranges and tamarinds, feasting at every opportunity on tropical fruit after three awful weeks at sea.

Darwin was so seasick at the start of his five-year voyage aboard the HMS Beagle that the captain expected him to jump ship back to England as soon as they touched land. But he found his feet on the island he called St. Jago, where he spent his first hours strolling through coconut groves and “hearing the notes of unknown birds, & seeing new insects fluttering about still newer flowers.”

Most travelers questing after Darwin head to the Galápagos Islands, where an entire tourist industry has developed around his legacy. It was the Galápagos where Darwin, according to popular legend, “discovered” natural selection — though, in reality, it was only later in London that he grasped the significance of the finches and other animals he collected there. Still, by the time Darwin reached the Galápagos in 1835, he was a seasoned naturalist who had spent nearly four years on the Beagle.

The Darwin who arrived on Santiago on Jan. 16, 1832, was naïve and untested, with only European soil beneath his fingernails. Cape Verde, then a Portuguese colony, gave Darwin his first taste of his own scientific talent. “He caught a glimpse of his own powers and recognized a new kind of desire — the wish to make a contribution to the world of philosophical natural history,” wrote Janet Browne, his biographer.

An island’s inspiration

Today, Cape Verde is an independent nation of 10 islands and nearly 600,000 citizens speaking Creole and Portuguese. Tourists from Europe usually head to Sal and Boa Vista, where resorts partition white-sand beaches; adventurous visitors climb the active volcano on Fogo or celebrate Carnival on São Vicente.

More Cape Verdeans live on Santiago, though, than any other island. The architecture, music and cuisine blend West African and Portuguese influences: In the capital, Praia, you can snack on papaya from the market or pastel de nata, a Portuguese custard pastry, from a bakery.

Santiago stood out to me ever since I read Darwin’s life story. I wanted to see the island that inspired him to become the scientist we celebrate today. So, last March I checked into the Boutique Hotel Praia Maria, a simple hotel on Rua 5 de Julho, a pedestrian boulevard in the Plateau, Praia’s historic center.

Across from the hotel, an enormous mastiff paced on a red tile roof, barking at passers-by below: women selling strawberries and SIM cards, men in suits headed to government ministries, German cruise-ship passengers huddled around tour guides.

Eager to see where the Beagle docked, I made my way down the boulevard, past the cafes serving cachupa, a stew of corn, beans and root vegetables, and square sobrado townhouses with painted shutters and open doorways revealing shelves of groceries and souvenirs. The road led through the main square dominated by a colonial church to a cliff-top promenade with a statue of the Portuguese explorer Diogo Gomes presiding over the harbor.

A modern port operates now on the harbor’s eastern edge; the Beagle’s base was an islet in the center, which Darwin called Quail Island and is known today as Ilhéu Santa Maria. On the harbor beach, some fishermen agreed to take me to the islet by boat. While they cracked tiny clams with rocks and ate them raw, I gazed into tidal pools with carpets of pink and green coral. It was in pools like these that Darwin found octopuses that changed colors and seemed to glow at night. He wrote a mentor in England describing his first big discovery — only to learn later that the octopus’s powers of camouflage were already well-known.

A budding geologist?

For all of Darwin’s rhapsodizing about Santiago’s tropical fruits, the island is largely dry, brown and inhospitable outside a few irrigated valleys. “Nature is here sterile, nothing breaks the absolute stillness, nothing is seen to move,” Darwin wrote. The most common animals, he noted, were an endemic sparrow and a kingfisher with a gray head and bright-blue tail feathers — “the only brilliantly colored bird which I saw.” I observed the same birds nearly everywhere I went on Santiago, as well as cattle egrets, guinea fowl, brown-necked ravens and collared doves.

Santiago’s animals did not spark Darwin’s interest in the origin of species. He was more curious about the rocks. “Geology is at present my chief pursuit & this island gives full scope for its enjoyment,” he wrote in his diary.

In that spirit, I hired a local geologist named Jair Rodrigues as my guide. “I know every road of Cape Verde,” Mr. Rodrigues assured me. He picked me up at my hotel in a red pickup and we drove along the edge of the harbor on a road called Avenida Charles Darwin — one of the island’s few memorializations of his visit.

“Cape Verdeans don’t really know Darwin,” said Mr. Rodrigues, who carried a book by António Correia e Silva, an island historian who laid out a “Darwin trail,” of sorts, around Praia.

Our first stop, though, wasn’t on the map: an unfinished housing subdivision on the southeast tip of Santiago. The deserted neighborhood ended at a cliff with a bike lane beneath a string of lampposts, which could have been grafted from Amsterdam. We walked through scrubland and down a narrow trail on the face of the cliff, our footsteps unloosing gravel into the thrashing Atlantic.

“On entering the harbor, a perfectly horizontal white band in the face of the sea cliff, may be seen running for some miles along the coast,” Darwin recounted in “The Voyage of the Beagle.” His teachers believed the earth’s features had been formed by violent cataclysms, but on the Beagle Darwin had been reading “The Principles of Geology” by Charles Lyell, a Scotsman who argued that the earth was shaped by gradual processes unfolding constantly over long stretches of time.

Lyell’s work taught Darwin to see nature as the accumulation of tiny, incremental changes, a perspective that would inform his thinking later, as he studied the plants and animals he had collected on his journeys. When developing his theory on the origin of species, Darwin said he was merely “following the example of Lyell in Geology.”

Speculating on the origins of Santiago’s rocks was “like the pleasure of gambling,” he told a friend. That white band of limestone he noticed was sandwiched between two thicker layers of black basalt and became especially apparent on the sea cliff Mr. Rodrigues showed me. Darwin reasoned that the bottom layer must have flowed into the sea from the island after a volcanic eruption. The limestone accumulated on top as small aquatic creatures died and fell to the sea floor. Another eruption then sealed the limestone beneath a second layer of basalt, before the entire structure rose from the sea. Piecing this together, Darwin wrote later, “convinced me of the infinite superiority of Lyell’s views.”

An enormous baobab and a ‘wild song’

Mr. Rodrigues drove me along the southern coast of Santiago to Cidade Velha, the first European town in the tropics and a UNESCO World Heritage site. We sat on the veranda of a beach restaurant and watched spear fishermen haul in yellowfin tuna, which we ate from the grill.

In town, schoolchildren crowded into the main square around an obelisk memorializing the slave trade. The Portuguese arrived in Santiago in the 15th century and used the island as a waypoint between West Africa and Brazil. Darwin mentions slavery only briefly in his Santiago journals — he suspected a “very pretty schooner” in the harbor of being “a slaver in disguise” — but was repulsed by the cruelty he soon witnessed in South America.

The main road of Cidade Velha led uphill to the ruins of the oldest church south of the Sahara, where centuries-old tombstones are still legible in the rubble. Pirates ransacked Cidade Velha repeatedly, and in 1770 the Portuguese moved the capital to Praia, which was easier to defend. Traditional stone homes lined an old side street called Rua Banana, some of the houses hugging the curb so closely that you could practically knock on their wooden doors from the center of the road.

We continued to a village in the interior called São Domingos. On the way, Mr. Rodrigues turned into a narrow valley and parked beneath an enormous baobab tree on a dirt road between two fields of sugar cane. Baobabs bear leaves only a few months of the year, and the tree was bare except for some fuzzy brown fruits dangling from its branches. (Their juice, called calabaceira, is thick, velvety and slightly sour — and was my favorite part of breakfast in Praia.)

Visitors had carved their names into the gray bark of the baobab’s bloated trunk — a whim that, apparently, goes back centuries. When he passed by here, Darwin said the tree was “completely covered with initials & dates as any one in Kensington Gardens.” He measured the tree — 13 feet in diameter and no more than 30 feet tall — and felt that the numbers showed how “a faithful delineation of Nature does not give an accurate idea of it.”

In his journals, Darwin wrote that he got lost trying to hike to São Domingos in the barren, featureless land. When he finally found the village, he was delighted by the coconut, guava, sugar cane and coffee growing in the fields. “I can imagine no contrast more striking than that of its bright vegetation against the black precipices that surround it,” he wrote. After “a most substantial dinner of meat cooked with various sorts of herbs & spices & Orange Tart,” Darwin passed 20 young women dressed in bright turbans and shawls. The women broke into dance and “sung with great energy a wild song, beating time with their hands upon their legs.”

Later, Mr. Rodrigues took me to a restaurant and garden called Eco Centro. The kitchen was closed, but we wanted to admire the view from the patio overlooking the village’s corrugated metal rooftops and the jagged mountains across the valley.

The owner, an older man named Filomeno Soares, pointed to a fenced-in plot where he planned to cultivate some of the local species Darwin collected on the island. He was also preparing a new menu with orange tart and arranging performances of the dance Darwin had observed, called batuque, by village women.

He was developing the Darwin-themed attractions with a businesswoman in Praia named Marvela Rodrigues, who wanted to attract visitors to Santiago as an alternative to more touristy islands like Sal and Boa Vista. “We don’t have all-inclusive resorts on Santiago,” she told me. “We focus on culture and history.”

A few months after my trip, Ms. Rodrigues’s company, Sandymar, installed signboards at many of the locations along the “Darwin Way” mapped in Mr. Silva’s book. Perhaps Cape Verdeans would have new opportunities, after all, to learn about the curious Englishman who visited their capital all those years ago.

A second visit

After three weeks on Santiago, the Beagle’s captain no longer worried about Darwin’s resolve. “A child with a new toy could not have been more delighted than he was with St. Jago,” he wrote. Darwin, writing in his diary, was itching to forge ahead: “I am becoming rather impatient to see tropical Vegetation in greater luxuriance than can be seen here.”

When the Beagle returned to Santiago nearly five years later, at the end of his journey, Darwin devoted only a few paragraphs in his journal to the visit — including a mention of “our old friend the great Baobab tree.”

But years later, writing his autobiography as an old man, the island shined brightly in his memory: “How distinctly I can call to mind the low cliff of lava beneath which I rested, with the sun glaring hot, a few strange desert plants growing near, and with living corals in the tidal pools at my feet.”

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