How the Galapagos changed Darwin’s thinking – and why mockingbirds, rather than the famous finches, provided an important early clue.
“The natural history of this archipelago is very remarkable: it seems to be a little world within itself” – Charles Darwin
No scientist is more closely associated with the Galapagos than Charles Darwin. His name can be found throughout the archipelago, from statues and street names to remote Darwin Island in the far north.
Yet the familiar story that Darwin looked at a few finches in the Galapagos and developed his theory of evolution there and then is not quite true. He spent just five weeks in the islands and, during that time, was at least as interested in volcanoes and rocks as he was in birds.
A far less conspicuous bird probably played a more important role in his early suspicions: the Galapagos mockingbird.
And Darwin was not ultimately the only person to arrive at the idea of natural selection. More than twenty years after his visit to the Galapagos, he received a letter from Alfred Russel Wallace that suddenly set events in motion.
Charles Robert Darwin was born in Shrewsbury, England, in 1809. He first studied medicine in Edinburgh and later attended Cambridge. Shortly after completing his studies, he was given the opportunity to sail aboard HMS Beagle under the command of Captain Robert FitzRoy.
The voyage began in December 1831 and would eventually last almost five years. The Beagle’s principal task was to conduct hydrographic surveys and improve the mapping of, among other areas, the coastlines of South America.
Darwin joined the voyage as a young gentleman-naturalist. He collected plants, animals, fossils and rocks, while keeping extensive notes on the natural world he encountered along the way.
On 15 September 1835, the Beagle reached the Galapagos.
Darwin could not yet have imagined how important these remote islands would later become to his scientific work.
During his stay, Darwin visited four islands: San Cristóbal, Floreana, Isabela and Santiago. The Beagle also sailed past several other islands without Darwin going ashore.
On San Cristóbal, he mainly studied the volcanic landscape. But a mockingbird also caught his attention. He began to wonder how the animals and plants of these isolated islands were related to those of the South American mainland.
On Floreana, he encountered another mockingbird and immediately noticed that it differed from the bird he had collected on San Cristóbal. Residents also told him that they could identify which island a giant tortoise came from simply by its appearance.
On Isabela, the Beagle anchored at Tagus Cove. Darwin once again studied the island’s geology and collected birds and other specimens.
His longest stay ashore was on Santiago. While the Beagle sailed elsewhere in the archipelago, Darwin remained there with several crew members. He encountered large numbers of giant tortoises and continued collecting plants and animals.
On 20 October 1835, the Beagle left the Galapagos behind.
Today, almost everyone has heard of Darwin’s finches. Their different beak shapes are frequently used to illustrate how species can adapt to different food sources and environmental conditions.
But while he was in the Galapagos, Darwin had not yet recognised the significance of these finches.
He collected a number of specimens, but did not carefully record the island of origin for every bird. This made it difficult to reconstruct their distribution across the archipelago afterwards.
The mockingbirds were different.
Darwin had collected specimens from different islands and noticed that they varied. It was intriguing. How could islands relatively close to one another, with similar climates and similar volcanic origins, be inhabited by their own distinct varieties of animals?
It was a question that extended far beyond the Galapagos.
After Darwin returned to England, his birds were examined by the renowned ornithologist John Gould. He showed that several birds Darwin had considered to be different kinds were, in fact, closely related finches. The differences between the mockingbirds also proved significant.
Gradually, a much bigger question began to emerge. Were species truly unchanging, as was widely believed? Or could they change over time and develop from common ancestors?
The Galapagos did not suddenly give Darwin his theory of evolution. They did, however, provide him with observations that would later help him think differently about species and their geographical distribution.
Darwin worked on his ideas for years without publishing his theory of natural selection.
Meanwhile, on the other side of the world, another British naturalist was considering a remarkably similar question.
Alfred Russel Wallace came from a very different background to Darwin. He was not born into a wealthy family and left formal education at a young age. Largely self-taught, he developed into an accomplished naturalist and collector.
He first travelled through the Amazon region and later spent years exploring the Malay Archipelago, in present-day Indonesia and surrounding areas. There, among other subjects, he studied the geographical distribution of animals.
Independently of Darwin, Wallace developed an idea strikingly similar to natural selection.
In 1858, he sent Darwin an essay outlining his theory.
For Darwin, reading it must have come as a shock. He had been developing similar ideas for around twenty years but had still not fully published his theory.
Geologist Charles Lyell and botanist Joseph Dalton Hooker helped find a solution that recognised the work of both naturalists. On 1 July 1858, writings by Wallace and Darwin were presented jointly at a meeting of the Linnean Society in London.
Neither man was present.
A year later, in November 1859, Darwin published On the Origin of Species. The book would change biology forever.
The basic principle of natural selection is surprisingly simple.
Individuals within a species vary. Some characteristics may provide an advantage for survival and reproduction in a particular environment. If these characteristics are inherited, they are more likely to be passed on to subsequent generations.
Over many generations, populations can therefore change. When groups remain isolated from one another for long periods and live under different conditions, those differences can eventually become so great that new species arise.
This is precisely what makes the Galapagos so remarkable.
The islands are isolated from the South American mainland, but the individual islands also form small worlds of their own. Populations could remain separated for long periods and develop under different conditions.
What Darwin observed in 1835 among mockingbirds, tortoises and other animals would therefore acquire a significance far greater than he could have imagined during his stay.
Travelling through the Galapagos today, you can still encounter much of what fascinated Darwin almost two centuries ago: black lava fields, giant tortoises, marine iguanas and birds found nowhere else on Earth.
But perhaps it is the inconspicuous mockingbird that tells the most fascinating story.
Not because a single bird suddenly led Darwin to discover the theory of evolution, but because the differences between seemingly similar birds on different islands helped him ask a far more fundamental question.
A question that would ultimately change our understanding of life on Earth forever.
