A Evolução de Darwin
Como habitualmente à sexta, comprei o Público e aproveitei a” oferta” do Livro sobre a Exposição de Darwin – Edição Gulbenkian -, por mais 15 euros, na compra do jornal.
Na manhã seguinte, encontrei o mesmo livro na loja da Gulbenkian, por 13,5 euros. Senti-me ludibriado e não gostei.
As primeiras pistas de Darwin
Comemora-se este ano o 150.º aniversário do livro mais incendiário da história da ciência e, coincidentemente, o 200.º aniversário do inglês de modos suaves que o escreveu. Charles Darwin não inventou a ideia da evolução, tal como Abraham Lincoln (que, por acaso, nasceu no mesmo dia, 12 de Fevereiro) não inventou a ideia da liberdade. O que Darwin ofereceu com “A Origem das Espécies” foi uma teoria consistente sobre a forma como a evolução pode ocorrer unicamente através de forças naturais, dando aos cientistas liberdade para explorar a gloriosa complexidade da vida em vez de a aceitar simplesmente como mistério impenetrável. “Nada em biologia faz sentido, excepto à luz da evolução”, escreveu há 36 anos o geneticista Theodosius Dobzhansky. Essa luz, que começou como um vislumbre na mente de um jovem naturalista a bordo do HMS Beagle, projecta actualmente raios tão fortes que podemos ler o texto da vida graças a ela. Darwin ficaria extasiado ao perceber quanto lhe ficara por saber e quanto nos resta ainda hoje por aprender. TEXTO DE David Quammen
O “erro” de Darwin
Fatigado por quase cinco anos de viagem, Darwin passou seis dias nos Açores em 1836, nada encontrando “que merecesse ser visto”. A omissão de Darwin foi lamentável, mas a ciência portuguesa pagou-lhe na mesma moeda e demorou alguns anos a interessar-se pela sua obra. TEXTO DE Luís Tirapicos
Ilha de Santiago, colónia portuguesa de Cabo Verde. Inverno de 1832. Na costa, a maré baixa deixou algumas poças onde um jovem britânico de 23 anos caminha. Divertido com a rapidez dos polvos, o naturalista Charles Darwin recolhe dados escrupulosamente. Como escreveu mais tarde, “estes polvos apresentavam o seu poder tipo-camaleão durante o acto de nadar e quando permaneciam no fundo.
Diverti-me imenso pelas várias artes para escapar à detecção usadas por um indivíduo, que parecia perfeitamente ciente de que o observava. Permanecendo imóvel por algum tempo, avançava vagarosamente uma ou duas polegadas, como um gato que persegue um rato; por vezes, alterava a sua cor: então prosseguiu até atingir uma região mais profunda, e precipitou–se, deixando um rasto de tinta para esconder o buraco para onde se arrastara.”
O HMS Beagle, com Darwin a bordo, partira de Devonport a 27 de Dezembro de 1831, ancorando na actual Cidade da Praia a 16 de Janeiro. O objectivo da viagem era concluir o levantamento topográfico da Patagónia e da Terra do Fogo, bem como realizar medições cronométricas em torno do globo. A circum-navegação duraria quase cinco anos.
Matt Ridley escreveu o livro “Francis Crick: Discoverer of the Genetic Code”
David Reznick, Biólogo
Constance Scharff, Bióloga
Neil Shubin, Paleontologista e Biólogo, Bolseiro da National Geographic Society
Hopi Hoekstra, Bióloga especializada em Evolução
Sean Carroll, Geneticista
COMO NOS TORNÁMOS HUMANOS?
Novos conceitos e poderosas ideias acompanharam o estabelecimento das sociedades modernas que hoje povoam a Europa, tais como o heliocentrismo (que Copérnico foi beber à Itália renascentista) implicando que o nosso planeta tenha uma origem comum – a poeira cósmica; o movimento uniforme como estado de equilíbrio no universo e não o do repouso (o princípio da relatividade de Galileu); a gravidade como explicação dos fenómenos nos céus e na Terra (a atracção universal de Newton); a origem comum das espécies vivas neste planeta (a teoria da evolução de Darwin); e a equivalência entre massa e energia que permitiu a Einstein unificar as causas e a dinâmica dos corpos em movimento.
Entre estes, aquele que provocou mais acesos e emocionados debates foi sem dúvida o da evolução dos seres vivos por selecção natural na luta pela sobrevivência. Perceberam as elites dirigentes, bem como os donos dos princípios éticos e morais da época, que a teoria de Charles Darwin vinha relegar para o infinito o último elo com o Além que ainda restava na natureza: o da origem divina dos seres humanos.
Os conceitos de evolução, de transformação e de adaptação, mostram como a mudança é omnipresente em tudo o que se relaciona com a nossa realidade – nas suas três vertentes: a exterior, a social e a interior.
A investigação científica em biologia mostra igualmente como a evolução e a selecção dos seres vivos está a acontecer todos os dias, em todos os instantes. É, assim, fundamental que encaremos o mundo segundo
uma perspectiva que acolha os ensinamentos da ciência. Só é possível mudar o mundo se mudarmos o modo como o olhamos – e tornarmos consequente essa mudança. É isso que fazem todos os povos que
apostam no seu futuro.
A Fundação Calouste Gulbenkian vai por este motivo realizar uma exposição intitulada “A Evolução de Darwin” entre 12 de Fevereiro e 24 de Maio de 2009, para comemorar os 200 anos do nascimento de Charles Darwin e, simultaneamente, a passagem de 150 anos sobre a publicação da sua obra seminal “A Origem das Espécies”.
O presente ciclo de conferências pretende que todos se iniciem ou (se já iniciados) prossigam “No Caminho da Evolução”, criando continuamente imagens construtivas e positivas de si próprios e dos outros, na interacção com a sociedade e o meio ambiente, preparando o clima de saudável circulação de ideias e de aprendizagem que a Exposição de 2009 certamente proporcionará.
João Caraça, Director do Serviço de Ciência
Vídeos Conferências DARWIN: No Caminho da Evolução
E. O. Wilson (1929 – )
Eugene Odum (1913-2002)
Ernst Haeckel (1834-1919)
Jean Jacques Audubon (1785-1851)
Albrecht von Haller (1708-1777)
Carl Linnaeus (1707-1778 )
Pedanius Dioscorides (40-90 D.C.)
Theophrastus (371-286 A.C.)
All About Darwin
Happiest at home with his notebooks and his microscope, he shunned the public eye. Controversy made him ill. This brilliant observer of nature kept his most original and revolutionary idea under wraps for decades. Yet today, two centuries after Charles Darwin’s birth, nearly everyone knows his name. What did Darwin do, and why does he still matter so much?
Keenly observing nature in all its forms—from fossil sloths to mockingbirds, primroses to children—Darwin saw that we all are related. Every living thing shares an ancestry, he concluded, and the vast diversity of life on Earth results from processes at work over millions of years and still at work today. Darwin’s explanation for this great unfolding of life through time—the theory of evolution by natural selection—transformed our understanding of the living world, much as the ideas of Galileo, Newton and Einstein revolutionized our understanding of the physical universe.
Darwin’s theory of evolution by natural selection underlies all modern biology. It enables us to decipher our genes and fight viruses, and to understand Earth’s fossil record and rich biodiversity. Simple yet at times controversial, misunderstood and misused for social goals, the theory remains unchallenged as the central concept of biology. Charles Darwin, reluctant revolutionary, profoundly altered our view of the natural world and our place in it.
Looking at Life
Charles Darwin looked closely at life. The vast and marvelous diversity of life on Earth, from barnacles to butterflies, ostriches to orchids, made him curious. Countless species, living and extinct—why so many? Some were only slightly different from one another-what could explain that? Each organism so beautifully adapted to its environment—how could it happen?
With persistence and passion, Darwin set out to find answers. He conducted experiments. He read widely and corresponded with fellow naturalists around the world. And he studied the evidence using simple tools, at times little more than a microscope or a magnifying glass. Darwin looked closely—and we saw the world in a new way.
The World Before Darwin
Before Darwin was born, most people in England accepted certain ideas about the natural world as given. Species were not linked in a single “family tree.” They were unconnected, unrelated and unchanged since the moment of their creation. And Earth itself was thought to be so young—perhaps only 6,000 years old—that there would not have been time for species to change. In any case, people were not part of the natural world; they were above and outside it.
These attitudes reflected a broader view of the world as stable and unchanging. There was a natural order to things. Most English people lived in farming communities and did not travel far from where they were born. Their lives were much like the lives of their parents. Soon the Industrial Revolution and democratic reforms would remake society—but before Darwin, it was still possible to see the world as timeless, eternal and unchanging.
Today, we know from radiometric dating that Earth is about 4.5 billion years old. Had naturalists in the 1700s and 1800s known Earth’s true age, early ideas about evolution might have been taken more seriously.
The Nature of Species
By 1800, European naturalists knew a great deal about plants and animals. They collected specimens, carefully studied them and even classified similar species in groups. But only a few bold thinkers, including Jean-Baptiste Lamarck and Erasmus Darwin, Charles’s grandfather, speculated that species had evolved—that is, that all life shared a common ancestor.
Why didn’t more people grasp that similarities in skeletal structures—so clearly visible—were a clue that species are related? In part, no one could convincingly explain how evolution worked. How could distinctive features, like the anteater’s long nose, have taken shape over time? How could new species arise? Few naturalists, however, were even asking such questions. Most were comfortable with the prevailing view that each species resulted from an act of special creation by a Creator.
Evolution Before Darwin
Early evolutionists like Jean-Baptiste Lamarck had difficulty explaining how new species arose. Lamarck saw that many animals seemed to have acquired useful adaptations. The giraffe’s long neck, for instance, was perfect for feeding on high leaves. But how did the giraffe get its neck? Lamarck thought it resulted from the constant effort of reaching for food. Constant use of a body part, he argued, made it larger and stronger.
But there was one key problem. Can changes produced during an animal’s lifetime be passed on to its offspring? Does a father lifting weights produce a muscular baby? Lamarck argued that such acquired traits could be inherited, but few others were persuaded. A convincing mechanism for evolution had yet to be discovered.
Not Just Another Animal
Before Darwin’s time, humans were not considered part of the natural world. People saw that we resembled other animals, especially other primates like the orangutan and the chimpanzee. Still, despite the undeniable similarities between “us” and “them,” only a handful of early naturalists classified humans, too, as animals.
In England during the 1700s and early 1800s, few questioned the Biblical story of creation. The prevailing view was that people were created to rule over animals, “over the fish of the sea and over the birds of the sky.” Naturalists could see that, particularly beneath the skin, a chimpanzee looks a lot like a human—but the idea that we might somehow be related to apes was almost unthinkable.
Birds’ eggs and sea shells, beetles and coins, moths and minerals—as a child, Charles Darwin collected all of these and more. Born in 1809 to a wealthy family in rural England, he spent hours watching birds and lying under the dining-room table, reading. He was an indifferent student, though, and school bored him. He despaired of learning Latin and memorizing verse, “for every verse was forgotten in 48 hours.” But he never tired of studying the details of the natural world.
As a teenager, Darwin was thrilled by chemistry, biology, botany and geology. Yet all the while he dutifully pursued the careers his father had selected for him: doctor and then clergyman. As he studied at the University of Cambridge, though, Darwin was singled out by an elite circle of academics who recognized his potential. Finally, his true talent for natural history blossomed.
The Wedgwood Family
The Charles Darwin’s mother, Susannah, was the daughter of Josiah Wedgwood, founder of England’s world-renowned Wedgwood pottery. Still widely admired today, Wedgwood pottery was a technical marvel in the 1700s, and Wedgwood’s factory was a leading example of Britain’s dawning Industrial Revolution. Wedgwood’s state-of-the-art factory, Etruria, included living quarters for his workers, a church and a school, which both of Charles’s parents attended as children.
Darwin’s parents represented the union of two prominent, wealthy families, the Darwins and the Wedgwoods. Though not aristocrats, both families embodied the emerging class of progressive, technology-minded entrepreneurs. The families were linked by friendship, business and multiple marriages: Charles’s father, his sister and eventually Charles himself all married Wedgwoods.
The Darwin Family
Charles Darwin’s paternal grandfather, Erasmus Darwin, made the Darwin name famous well before Charles was born. Erasmus was accomplished in many different fields. One of England’s leading medical authorities, he was asked to be the personal doctor of King George III. He was a prolific inventor whose achievements included a horizontal windmill to power the Wedgwood factory. He was also a popular poet and natural philosopher whose ideas were credited with inspiring Mary Shelley’s novel Frankenstein.
Erasmus’s radical views included opposition to slavery, support for women’s education, sympathy for the French and American revolutions and a theory of evolution that predated Charles Darwin’s by several decades.
Erasmus’s son Robert—Charles’s father—was also a physician. But unlike his outspoken father, Robert was sober and respectable. Charles accordingly grew up in a dignified, upstanding household.
Shooting, Dogs, and Rat-catching
Darwin’s mother, Susannah, died when Charles was only eight. Even before her death, she was a distant presence because sickness often kept her bedridden. Darwin claimed, “I can remember hardly anything about her.” The loss was cushioned by the attention of his three older sisters, who doted on the two youngest children, Charles and Catherine. Charles was also very close to his brother Erasmus all his life.
The year after his mother’s death, Darwin was sent to a local boarding school near his home in Shrewsbury. He hated the school’s stifling curriculum based on rote memorization of Greek and Latin. “Nothing could have been worse for the development of my mind than Dr. Butler’s school,” Darwin recalled.
Impatient with Charles’s lack of progress, Darwin’s father pulled him from the school and sent him to Edinburgh University in Scotland to study medicine, like his father and grandfather before him. When Charles showed no interest in becoming a doctor, Robert exploded, “You care for nothing but shooting, dogs, and rat-catching, and you will be a disgrace to yourself and all your family.” His father next sent Charles to the University of Cambridge to prepare for a career in the church. Charles had no objection. A quiet country parish might be just the place to pursue his interest in natural history.
A Lifelong Passion
Although bored at times by formal schooling, the young Charles Darwin poured enormous energy into his fascination with the natural world. As a boy, tired of Greek and Latin, he did chemistry experiments in a homemade lab with his brother Erasmus. At Edinburgh University, instead of studying medicine, he wrote his first scientific papers. And at Cambridge University, where he was sent to become a clergyman, he became so devoted to botany that he took the sole botany course three times.
One scientific hobby, however, stood out above all: collecting beetles. Darwin got into a heated rivalry with another Cambridge student, Charles “Beetles” Babington, over who would acquire a new species first. And when he wasn’t collecting beetles, he was writing excited letters to his cousin William Darwin Fox, confessing, “It is quite absurd how interested I am getting about the science.”
First Scientific Paper
While at Edinburgh University, Darwin was encouraged by a free-thinking professor and early evolutionist, Robert Grant, who was an admirer of the evolutionary writings of Jean-Baptiste Lamarck and Erasmus Darwin, Charles’s grandfather. Grant was especially interested in primitive sea life like sponges and bryozoans—literally, “moss animals”—because he believed all plants and animals shared a simple marine ancestor. Darwin, too, became interested in this idea and in 1827 presented a paper to a student group on a bryozoan called Flustra.
Revenge of the Beetles
Not all the beetles Darwin captured gave up without a fight. Many beetles, including the Brachinus crepitans and the Stenaptinus insignis, release irritating chemicals as a defense. Darwin experienced one such defense first-hand:
“One day, on tearing off some old bark, I saw two rare beetles, and seized one in each hand; then I saw a third and new kind, which I could not bear to lose, so that I popped the one which I held in my right hand into my mouth. Alas! it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as was the third one.”
A World of Change
When Charles Darwin was a student in the 1820s, no science exerted a stronger hold on the popular imagination than geology. The public followed the latest theories and discoveries in amazement. Thousands bought books on the subject, and debates on the history of the Earth and its formation raged among scientists.
By this time, geologists had shown that Earth was not static or fixed—clearly it had undergone sweeping changes over time and was, in fact, still changing. This idea had a huge influence on Darwin’s thought. Pondering the long, slow changes in Earth’s history would later help shape Darwin’s ideas about how plant and animal species, too, had changed over millions of years.
Shifting Layers of Rock
The exposed layers of rock at Siccar Point, Scotland, tell a dramatic story of the ever-shifting movement within the Earth. Beneath the nearly horizontal layers of red sandstone, one can see vertical layers of gray slate. In the late 1700s, Scottish geologist James Hutton realized that these cliffs revealed a long, slow process. The vertical layers were originally laid down horizontally, then lifted and tilted by forces within the Earth. After being worn down by erosion, they sank underwater and were covered by sediment. This sediment also became rock, forming the red upper layers. Later the whole structure emerged above the water.
Such insights changed the way people understood Earth’s history. Geology showed that Earth was much older than the Bible implied—processes like these would require millions of years. According to Hutton, Earth had been constantly changing for so long that there was “no vestige of a beginning, no prospect of an end.”
At the University of Cambridge, Darwin’s interest in natural history blossomed into far more than a hobby. An elite circle of prominent professors served as mentors and role models for Darwin. He became the particular protégé of the Reverend J. S. Henslow, a brilliant and charismatic botanist. Darwin called meeting Henslow the event “which influenced my career more than any other.”
Henslow was known for his popular botany lectures and field outings. “It was obvious that Darwin was Henslow’s favorite pupil,” a fellow student recalled. “Professor Henslow used to say ‘What a fellow that Darwin is for asking questions!'” The two became so close that Darwin was known as “the man who walks with Henslow.”
Encouraged by Henslow, Darwin developed a “burning zeal to add even the most humble contribution to the noble structure of natural science.” To help him brush up on his geology, Henslow introduced Darwin to Adam Sedgwick, one of Britain’s preeminent geologists. Reverend Sedgwick took Darwin on an eye-opening geological expedition through Wales. Darwin recalled, “This tour was of decided use in teaching me a little how to make out the geology of a country”—a skill Darwin would need much sooner than he imagined.
“A Tropical Glow”
After a flurry of studying over Christmas break, Darwin passed his degree exam in January 1831, finishing tenth on a list of 178. He remained at Cambridge two more terms, during which he became obsessed by a desire to travel and began planning a trip to the Canary Islands. “My head is running about the Tropics,” he wrote his sister Caroline. “My enthusiasm is so great that I cannot hardly sit still….I have written myself into a tropical glow.”
A Trip Around The World
In 1831, Charles Darwin received an astounding invitation: to join the HMS Beagle as ship’s naturalist for a trip around the world. For most of the next five years, the Beagle surveyed the coast of South America, leaving Darwin free to explore the continent and islands, including the Galápagos. He filled dozens of notebooks with careful observations on animals, plants and geology, and collected thousands of specimens, which he crated and sent home for further study.
Darwin later called the Beagle voyage “by far the most important event in my life,” saying it “determined my whole career.” When he set out, 22-year-old Darwin was a young university graduate, still planning a career as a clergyman. By the time he returned, he was an established naturalist, well-known in London for the astonishing collections he’d sent ahead. He had also grown from a promising observer into a probing theorist. The Beagle voyage would provide Darwin with a lifetime of experiences to ponder—and the seeds of a theory he would work on for the rest of his life.
A Very Small Vessel
Darwin knew that life would be cramped aboard the Beagle, but it was still a shock to see how small the ship was: just 90 feet long. The poop cabin Darwin would share with two other men during the day measured just 10 feet by 11 feet—and part of it was taken up by a mast. The ship’s library lined one wall, and a large table filled most of the remaining space.
To sleep, Darwin hung a hammock over the table. He lay just two feet from the ceiling, looking up at the stars through a skylight that Captain FitzRoy thoughtfully installed.
A Five-Year Journey
The captain and crew of the HMS Beagle originally planned to spend two years on their trip around the world. Instead, the voyage took nearly five years, from December 1831 to October 1836. The primary purpose of the trip, sponsored by the British government, was to survey the coastline and chart the harbors of South America, in order to make better maps and protect British interests in the Americas.
In addition to the ship’s official mission, however, it was understood that Darwin was to make scientific observations. So while the ship systematically measured ocean depths, Darwin went ashore to explore and collect specimens. In fact, two-thirds of Darwin’s time was spent on dry land, largely in the South American wilderness of Brazil, Argentina, Chile and remote areas such as the Galápagos Islands. By any measure, Darwin’s labors were hugely successful. He brought back specimens of more than 1,500 different species, hundreds of which had never before been seen in Europe.
December 27, 1831
After months of delays, the Beagle finally departs. “The misery I endured from sea-sickness is far beyond what I ever guessed at.”
Darwin has dreamed of visiting Tenerife for a year, but a cholera quarantine forces the Beagle to pass without stopping.
Cape Verde Islands
“It then first dawned on me that I might perhaps write a book on the geology of the various countries visited, and this made me thrill with delight.”
Darwin explores Brazilian rain forests for the first time. “Here I first saw a tropical forest in all its sublime grandeur.…I never experienced such intense delight.”
Rio de Janeiro
On a 150-mile trek inland, Darwin is appalled by the cruel treatment of slaves.
“I have been wonderfully lucky with fossil bones. Some of the animals must have been of great dimensions: I am almost sure that many of them are quite new.”
Tierra del Fuego
Captain Robert FitzRoy repatriates three native people he had brought to England on a previous voyage; he attempts to start a Christian mission, which fails disastrously.
Darwin collects distinctive island birds and fossils that offer a startling contrast to mainland species.
Darwin explores the Pampas with local gauchos.
“There is high enjoyment in the independence of the Gaucho life-—to be able at any moment to pull up your horse, and say, ‘Here we will pass the night.’ “
Strait of Magellan
Two and a half years into the voyage, the Beagle at last reaches the Pacific Ocean.
Darwin witnesses the eruption of Mount Osorno.
Darwin experiences an earthquake in Valdivia and later visits the leveled town of Concepción. He notes that the coast rose several feet.
Darwin climbs the Andes and finds petrified trees similar to those at sea level. He becomes certain the mountains rose “slowly and by little starts,” in a long series of earthquakes.
Darwin finds plants, birds and tortoises with many variations unique to the Galápagos Islands, but that seem mysteriously related to mainland species.
Marveling at marsupials, Darwin wonders why there is a whole different set of mammals in Australia.
Cocos Islands (aka Keeling Islands)
Darwin studies coral atolls to test his theory of reef formation. “I am glad we have visited these islands; such formations surely rank high amongst the wonderful objects of this world.”
“It’s a complete & very beautiful picture. But, there is no country which has now any attractions for us, without it is seen right astern, & the more distant & indistinct the better. We are all utterly home sick.”
Cape of Good Hope
Darwin visits the English scientist John Herschel, who like Darwin was curious about the origin of new species, which he called the “mystery of mysteries.”
Both homesick and seasick, Darwin is dismayed when the Beagle makes an unscheduled detour to South America for additional longitude measurements. “This zig-zag manner of proceeding is very grievous.…I loathe, I abhor the sea, & all ships which sail on it.”
October 2, 1836
“I reached home late last night. My head is quite confused with so much delight.”
But What To Bring?
With little time to prepare before the ship departed, Darwin hurriedly shopped for supplies. “It is such capital fun ordering things,” he wrote his friend Charles Whitley. Describing the same purchases to his family, however, he was careful to emphasize his frugality:
“I have procured a case of good strong pistols and an excellent rifle for 50 pounds, there is a saving; a good telescope, with compass, 5 pounds, and these are nearly the only expensive instruments I shall want.”
These are some of Darwin’s belongings from his Beagle voyage. He wouldn’t think of traveling without a Bible—after all, he still intended to become a clergyman when he returned. But he also needed weapons to survive on the rough-and-tumble South American frontier, including this a pistol and a “peacemaker,” or cosh, a small club to fend off robbers, rebels and revolutionaries.
His most important possessions, however, were his scientific instruments, such as his clinometer, a tool for measuring angles and elevations that he needed for geological observations. Just months before the voyage, Darwin had written to Sedgwick about his efforts to master the clinometer:
“I put all the tables in my bedroom, at every conceivable angle & direction. I will venture to say I have measured them as accurately as any Geologist going could do.”
An Emerging Mind
Darwin began the Beagle voyage green and inexperienced, but he finished a seasoned naturalist. And while he never lost his wonder and patience for close observation, on the Beagle he grew from a wide-eyed observer into a profound analytical thinker who increasingly found patterns in what he saw.
This gallery traces not a chronological journey but instead an internal one. It presents the development of the way Darwin saw the world—from delighted, detailed observations of individual species, to pondering the connections among them.
Here you will see clues that Darwin saw on the Beagle voyage, ultimately leading him to three insights about how living species are connected: to extinct species, to similar species living nearby and to others isolated on islands. In the years to come, all these initially puzzling relationships would eventually lead Darwin to a single conclusion—that all species are, in fact, related.
From his very first stop in South America, Darwin was overwhelmed by the splendors of the Brazilian jungle. Among the marvels he saw there were large green iguanas peering down at him from tree branches. Extremely common in South America, the green iguana can grow up to two meters (6½ feet) and can live 15 years. These animals are great climbers and spend most of their time in trees, eating leaves or sunning themselves.
“A Chaos of Delight”
In the year before his voyage, tantalizing pictures of lush South American jungles and the thrilling writing of Alexander von Humboldt had instilled in Darwin a longing to travel. But even the most vivid descriptions could not match his ecstasy at seeing the rain forest for himself:
“The delight one experiences in such times bewilders the mind,-if the eye attempts to follow the flight of a gaudy butter-fly, it is arrested by some strange tree or fruit; if watching an insect one forgets it in the stranger flower it is crawling over….The mind is a chaos of delight.”
Darwin’s first stop on the Beagle was in the Cape Verde Islands, where he was “overwhelmed” by seeing tropical plants and animals for the first time. “A child with a new toy could not have been more delighted,” Captain FitzRoy noted. Filled with excitement, Darwin wrote Henslow about an octopus that could change color, saying, “This fact appears to be new, as far as I can find out,” he told Henslow.
In fact, however, this species of octopus was already well known to other naturalists. Darwin was acutely aware of his youth and inexperience—in the same letter to Henslow, he added,
“One great source of perplexity to me is an utter ignorance whether I note the right facts, and whether they are of sufficient importance to interest others.”
An Amazing Octopus
At the first stop on his Beagle voyage, Darwin was amazed and enthralled to observe octopuses emit clouds of dark ink, squeeze into crevices, glow in the dark, squirt water at him, and change color like a chameleon.
“I was much interested, on several occasions, by watching the habits of an Octopus….By means of their long arms and suckers, they could drag their bodies into very narrow crevices; and when thus fixed, it required great force to remove them.”
Strange New World
Some of the most extraordinary animals Darwin encountered were those living on isolated islands like the Galápagos. Having lived for generations in a land free from hunters, many had no fear of humans. This made them easy prey. Darwin, who as a student at Cambridge had formed a club dedicated to eating animals “unknown to human palate,” cheerfully sampled the iguanas. He concluded,
“These lizards, when cooked, yield a white meat, which is liked by those whose stomachs soar above all prejudices.”
Many Galápagos animals were as strange as their surroundings, and they tended to blend with the lava around them. A few, though, such as the blue-footed booby and Sally lightfoot crab, had bright coloring; these were typically migrants from the mainland.
Named for a word meaning “foolish person,” boobies are known for their complete absence of defensive behavior. Though awkward when walking, blue-footed boobies are swift-flying seabirds that can dive from 80 feet and snatch a flying fish out of mid-air.
Black on Black
Of all the exotic new worlds that Darwin saw on his travels, none was more alien than the Galápagos Islands:
“Nothing could be less inviting than the first appearance. A broken field of black basaltic lava, thrown into the most rugged waves, and crossed by great fissures, is everywhere covered by stunted, sunburnt brushwood, which shows little signs of life.”
Darwin noticed that many species seemed a perfect match for their environment, even down to their coloring. Describing “most disgusting clumsy Lizards” that were “as black as the porous lava rocks over which they crawl,” Darwin mused, “They assuredly well become the land they inhabit.”
Though iguanas were common throughout South America, two species from the Galápagos Islands especially interested Darwin. These strange creatures appeared specially adapted for life there—and indeed could be found nowhere else. The marine iguana was especially distinctive: No other iguana swims or feeds in the ocean. Intrigued, Darwin opened the stomachs of several and found nothing but seaweed.
The other Galápagos iguana, Darwin observed, lived on land. It ate prickly pear cactus, spines and all. He was told it could go a year without drinking, getting all its water from the cactus plant. Darwin broke off a cactus branch and threw it to a small group, observing, “It was amusing enough to see them trying to seize and carry it away in their mouths, like so many hungry dogs with a bone.”
A Tree-Sized Cactus
On the Galápagos, Darwin found that normally smaller plants could be found in enormous sizes. The stems of some prickly pear cactus, Darwin noted, grew six to ten feet high and one foot in diameter.
The Galápagos marine iguana is well adapted to feeding in the ocean. It can stay underwater for an hour or more, and with its legs at its sides uses its flattened tail to swim like a crocodile.
Darwin engaged in a curious experiment with one of these iguanas. He repeatedly tossed it into the water, but instead of staying safely in the sea, it always returned and let him do it again. Marveling at this “apparent stupidity,” Darwin came up with an explanation: given the complete lack of natural predators on land, and the danger of sharks at sea, it instinctively fled to dry land whenever threatened.
Encounter with an Iguana
“Their limbs and strong claws are admirably adapted for crawling over the rugged and fissured masses of lava, which everywhere form the coast.”
Galápagos land iguanas often sit in the sun or bury themselves to hide or stay cool. Darwin wrote,
“I watched one for a long time, till half its body was buried; I then walked up and pulled it by the tail; at this it was greatly astonished, and soon shuffled up to see what was the matter; and then stared me in the face, as much as to say, ‘What made you pull my tail?'”
An Ever-Changing Earth
Throughout his trip, Darwin saw ample evidence that Earth had undergone vast changes. Mountains had risen from the sea. Climates had changed. Many species had gone extinct, leaving fossils as evidence. But how, Darwin wondered, had these changes occurred?
Darwin’s geological studies left him increasingly convinced that most of these changes had happened over a very long time. He climbed high into the Andes and found his proof: fossil tree trunks, still upright. Long ago, a forest must have been buried and slowly petrified. Then, in a long series of earthquakes, the land had been uplifted to form the Andes Mountains. As a result of the Beagle voyage Darwin would wonder: if mountains had taken shape over millions of years, was it possible that the same was true of species?
The Moving Earth
A turning point in Darwin’s thinking came when he experienced an earthquake that leveled the Chilean town of Concepción. To his amazement, the earthquake had elevated a bank of mussels about eight feet above the sea. If that could happen in one day, Darwin wondered, why couldn’t the same process, repeated over millions of years, raise entire mountains?
Darwin was fascinated by fossils, such as these pieces of petrified wood collected on his Beagle voyage. Petrified wood forms when trees are buried and over many years minerals seep in, slowly turning them to stone while preserving the structure of the ancient wood.
Darwin was especially interested in where he found each fossil. Studying the geology of the rocks, shells and fossils around it could reveal when the fossilized plant or animal lived. Fossils could also reveal how an environment had changed over time. For example, petrified wood had to start as living trees in a forest habitat, then spend time buried and later rise to its present elevation. Thus a single fossil could tell the story of a slowly changing landscape.
Even after the original material has been replaced by stony minerals, fine details of petrified wood are sometimes minutely preserved, down to the structure of individual cells.
One of the remarkable animals Darwin found and sent back to England was the ornate horned frog (Ceratophrys ornata). This pillow-shaped frog has been called a “mouth on legs.” It buries itself in leaves or loose soil and lies in wait, ready to gulp down whatever walks by—even animals larger than itself. The ornate horned frog lives in eastern Brazil and Argentina; similar, related frogs live in neighboring areas.
Collected by Charles Darwin
- Oxycara cribratum, Cape Verde Islands—1832
- Longitarsus sp. Bahia, Brazil—1832
- Canthidium trinodosum, Rio de Janeiro, Brazil—1832
- Prox pilularius, off Montevideo, Uruguay—1832
- Neobrachypterus darwini, Bahia Blanca, Argentina—1832
- Nyctelia rugosa, Bahia Blanca, Argentina—1832
- Brachinus platensis, Maldonado, Uruguay—1833
- Chanopterus brevipennis, Tierra del Fuego—1833
- Nyctelia fitzroyi, Port Desire, Argentina—1834
- Lathrididae, Concepción, Chile—1835
- Oedionychus fairmairei, Valparaíso, Chile—1835
- Parahelops darwini, Valparaíso, Chile—1835
- Scymnus galapagoensis, Charles I, Galápagos Islands—1835
- Oemona humilis, Bay of Islands, New Zealand—1835
- Allelidea ctenostomoides, Sydney, Australia—1836
- Anthicus strictus, Hobart, Tasmania—1836
- Phalacrus corruscans, King George’s Sound, Australia—1836
- Meligethes splendidulus, Cape of Good Hope, South Africa—1836
- Oxytelus alutaceifrons, St. Helena, Mid-Atlantic—1836
Collected by Charles Darwin
- Tatochila theodice gymnodice, Tierra del Fuego, Port Famine—1834
Collected by Charles Darwin
- Arctiidae South America—1834
- Arctiidae South America—1834
- Utetheisa pulchelloides darwini Keeling Islands—1836
- Utetheisa pulchelloides darwini Keeling Islands—1836
Collected by Charles Darwin
- Chloropidae, Chiloé, Chile—1834
- Paractora trichosterna, Falkland Islands—1834
- Prosopantium aequiseta, Falkland Islands—1834
- Anisopodidae, Tierra del Fuego, Port Famine—1834
- Hippoboscidae, St. Paul Rocks, Brazil—1832
Collected by Charles Darwin Specimen numbers: 31–33
- Kaapia darwini, Cape of Good Hope, South Africa—1834
- Caffrolix cyclopia, Cape of Good Hope, South Africa—1834
- Cephalelus sp., King George’s Sound, Australia—1834
While exploring the Falkland Islands, Darwin was interested to observe the behavior of the upland goose. Like birds on the Galápagos Islands, this goose had no instinctive fear of humans, and a hunter could kill “more of the upland geese in one day than he can carry home.” On the mainland, however, where it had been hunted for generations, Darwin noted that the same species was wary of hunters and avoided people. Clearly, a species could change over time in response to its environment, at least in its instinctive behavior.
The most extreme example of specialization Darwin saw in the Falklands was the Falkland Island steamer duck. Its beak is powerful enough to crush shellfish, its primary food, and its wings are used only as paddles. Darwin wrote,
“Their wings are too small and weak to allow of flight, but by their aid, partly swimming and partly flapping the surface of the water, they move very quickly. The manner is something like that by which the common house-duck escapes when pursued by a dog.”
A Ship and Its Captain
Captain Robert FitzRoy had extremely high standards for any ship he intended to command—and the money to back up his wishes. What the Admiralty wouldn’t pay for, he bought out of his own pocket. He claimed, with justification, “Perhaps no vessel ever quitted her own country with better or more ample supply (in proportion to her probable necessities) of every kind of useful provision.” The newly built cabins were outfitted in mahogany, the deck was raised to make more room to walk below and the hull was covered in copper.
FitzRoy was especially demanding about scientific instruments. To prevent the ship’s iron cannons from interfering with his precision compasses, he replaced them with brass cannons at his own expense. And after the Admiralty provided more than a dozen timepieces, which were used to measure longitude, FitzRoy insisted on buying six more, which only he and one other man were allowed to touch.
Crossing the Line
Tradition called for a raucous ceremony when crossing the equator. The tight ship’s discipline was eased for one day, as sailors “crossed the line.” Captain FitzRoy, dressed as Father Neptune, summoned the first-time equator-crossers for an alarming initiation. Darwin was blindfolded, flipped into a sail filled with water and roughly “shaved” with a piece of iron for a razor, and tar for shaving cream. Soon water was “flying about in every direction,” and “not one person, even the Captain, got clear of being wet through.”
The Beagle in the Strait of Magellan
A primary purpose of the Beagle’s mission was to chart the treacherous channels of the Strait of Magellan, on South America’s southern tip. Rough weather, high winds, and a maze of winding, rocky waterways made for dangerous sailing—one reason the Admiralty wanted more accurate maps.
Robert FitzRoy was a wealthy nobleman, a descendant of the Duke of Grafton and the Marquis of Londonderry. He was widely admired for his tight command of his men but had a fiery temper. Darwin felt FitzRoy’s wrath himself when he disagreed with him over slavery. Darwin detested slavery, and though usually diplomatic around the captain, he refused to accept FitzRoy’s opinion that Brazilian slaves were “happy.” FitzRoy became so angry that Darwin prepared to leave the ship, but the dispute blew over when FitzRoy apologized.
Evidence for Evolution: Fossils and Living Species
Fossils raised many questions about the origin of species—and not just for Darwin. Discoveries in geology had already challenged the idea that the world and all its species had been created at the same time a few thousand years ago. Fossils clearly showed that in past ages, the world had been inhabited by different species from those existing today. Old species had died out, and new species had appeared at many different times in Earth’s history.
Fossils also revealed another intriguing pattern: new species tended to appear where similar species had previously lived. Why would one species replace a similar one in the same location? Or perhaps, Darwin would eventually wonder, had the older species somehow given rise to the new ones? Back in London, the relationship between old and new species, as shown in fossils, would become one of the main lines of evidence leading to Darwin’s theory of evolution.
Darwin found the barren, windswept Falkland Islands “desolate and wretched.” Little grew there except “withered grass” and “a few very small shrubs.” But Darwin perked up when he cracked some “primitive looking rocks” with his hammer and found fossils. The Falklands were full of brachiopods—two-shelled animals that were once among the most abundant species on Earth. Excited about finding these clues to life in the distant past, Darwin wrote to Henslow describing his “high good fortune.”
Links to the Past
With 35,000 species living at different times over the past 570 million years, brachiopods are excellent for dating the rocks they are found in: Since rocks from different eras contain their characteristic species of brachiopods, one can determine the age of a rock layer by the type of brachiopod fossils found in it. Modern dating methods confirm the accuracy of this technique.
“I think the comparison of these impressions with those of the oldest fossiliferous rocks of Europe will be preeminently interesting.”
Darwin was delighted by the armadillos he saw scurrying about in Argentina. But most intriguing was the striking similarity of these small, armored mammals to some of the fossils he was unearthing. Among Darwin’s most dramatic finds was the “armour of a gigantic armadillo-like animal, the inside of which…was like a great cauldron.” This immense animal is called a glyptodont. To Darwin, many ancient, extinct species seemed to be giant versions of living species.
Darwin tried to figure out each fossil’s age from the age of the rocks and shells around it, and his new quest topped even his former passion:
“There is nothing like geology. The pleasure of the first days partridge shooting … cannot be compared to finding a fine group of fossil bones, which tell their story of former times with almost a living tongue.”
Why, Darwin wondered, had so many species gone extinct, only to be replaced by similar ones? And not just once, but again and again? Perhaps the newer species were better suited to the changing environment, he reasoned. All around him, he was seeing evidence of slow, gradual, geological changes. But if Earth’s changes were slow and gradual, what did that mean for the changes in species? Back in England, Darwin would ask himself: Over long periods of time, could older species have evolved into new ones?
Armadillos for Breakfast
Though Darwin was charmed by the armadillos’ behavior, he was equally interested in having a fine meal.
“In the morning we had caught an armadillo, which, although a most excellent dish when roasted in its shell, did not make a very substantial breakfast and dinner for two hungry men.”
Darwin’s search for fossils brought him back again and again to Punta Alta, on the coast of Argentina, where countless bones could be picked from the cliffs. His first visit produced a treasure trove of skulls and armor plates from six different animals. “I have been wonderfully lucky,” he wrote to Henslow; “many of them are quite new.” On a later visit he found “nearly an entire skeleton” of a giant ground sloth called Megatherium.
After two years of collecting, however, Darwin still had not heard whether any of his prized fossils had reached England. For all he knew, they were lying on the bottom of the ocean. Finally a letter arrived from Henslow. His fossils were safe in England, and Henslow urged Darwin to send back “every scrap of Megatherium skull you can set your eyes upon.- & all fossils.” Darwin resumed collecting with renewed vigor, and with confidence that he was on the right track.
Sloths the Size of Elephants
The three-toed sloth lives in the forests of South America. Sloths spend most of their time in the treetops, hanging from their curved claws and eating leaves. Extinct ground sloths like the ones Darwin collected were far too big to climb trees—some were the size of elephants. Darwin assumed the giant ground sloths instead used their curved claws to pull leafy branches down to them.
“This wonderful relationship in the same continent between the dead and the living, will, I do not doubt, hereafter throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.”
A Long Way From Home
All through the voyage, Darwin kept in touch by letter, writing to his father, sisters, brother, cousins, colleagues and school friends about his adventures. From his family he received regular updates on local politics and gossip. One by one, his cousins were marrying and settling down. News of the marriage of his old girlfriend, Fanny Owen, left him “melting with tenderness.” Later, his sisters reported that Fanny’s husband was “desperately selfish” and that she had been asking “prettily & coquettishly” about Charles—but it was too late. For the time being, Darwin threw himself into work.
Along with the personal connections, his letters cemented his professional ties to British scientists. Darwin sent crates of specimens and detailed letters to J. S. Henslow, his Cambridge mentor, describing plants, animals and geological observations. Far from isolating him from the scientific community, the voyage helped Darwin move into their circle. By his return, he was ready to take his place among them, not just as an accomplished observer and collector, but as a theorist.
Darwin sent numerous letters and specimens home by boat throughout the voyage. England was a thriving colonial power at the time, with a network of ships that literally spanned the globe, so Darwin could send and receive mail from almost anywhere in the world.
Letter: Charles Darwin to Robert Darwin
February 8-March 1, 1832
Page 4 of 11
Darwin’s lengthy letters home are filled with detailed, enthusiastic observations. As his father noted, “There is a natural good-humoured energy in his letters just like himself.” Early in the voyage, Darwin wrote his father an 11-page letter about the almost indescribable wonders of the tropics.
“Nobody but a person fond of Nat: history can imagine the pleasure of strolling under Cocoa nuts in a thicket of Bananas & Coffee plants, & an endless number of wild flowers.- And this Island that has given me so much instruction & delight, is reckoned the most uninteresting place, that we perhaps shall touch at during our voyage.…
It is utterly useless to say anything about the Scenery.-it would be as profitable to explain to a blind man colours….”
Despite his seasickness, which was far worse than anything he’d predicted, Darwin found that he liked living and working on a ship.
“I find to my great surprise that a ship is singularly comfortable for all sorts of work.- Everything is so close at hand.…if it was not for sea-sickness the whole world would be sailors.”
English Heritage (Down House)
Letter: Charles Darwin to J. S. Henslow
“Red-Hot with Spiders”
May 18-June 16, 1832
Page 4 of 6
In a letter to J. S. Henslow, Darwin describes his vast beetle collections, joking, “I tell Entomologists to look out & have their pens ready for describing.”
“I am at present red-hot with Spiders, they are very interesting, & if I am not mistaken, I have already taken some new genera.-I shall have a large box to send very soon to Cambridge…”
Darwin’s relationship with Henslow went well beyond business. Later in the letter he confides some personal feelings, including his longing for family and friends left behind and his gratitude for the help he received:
“I am sometimes afraid I shall never be able to hold out for the whole voyage. I believe 5 years is the shortest period it will consume.-The mind requires a little case-hardening, before it can calmly look at such an interval of separation from all friends.…
Tell Prof: Sedgwick he does not know how much I am indebted to him for the Welch expedition.-it has given me an interest in geology, which I would not give up for any consideration.”
Courtesy of the Archives of the Royal Botanic Gardens, Kew Folio 12; in volume of letters from Charles Darwin to Prof. Henslow
Charles Darwin’s “Beagle Notebooks,”
Cape Verde Islands to Rio de Janeiro;
Buenos Aires to the Chilean Andes
Date: ca. January-April 1832; ca. October 1833-August 1834
During his voyage, Darwin filled numerous notebooks with detailed observations on geology, plants and animals. These notebooks contain his notes from the Cape Verde Islands to Rio de Janeiro, Brazil, and from Buenos Aires, Argentina, to the Chilean Andes. Darwin was a precise and patient observer of animals, but his main interest at the time was geology. Over the course of the voyage, he made 368 pages of notes about animals but filled 1,383 pages with geology.
The raw observations Darwin put in his notebooks were just the starting point. Later he painstakingly transcribed them by topic into new notebooks, crossing out completed pages as he went—which is why most pages in his Beagle notebooks have a line through them.
Darwin mulled over his data on the trip back, puzzling out mysteries and searching for patterns. By the time he returned he had several books planned on geology and zoology—and some private lines of inquiry he intended to keep to himself.
Evidence for Evolution: Neighboring Species
The puzzling distribution of plants and animals in South America and the Galápagos would later make Darwin question how species originated. If each plant and animal was created to match its habitat, why didn’t the same species appear in similar environments? Why create the ostrich in Africa and a different running bird, the rhea, in America?
And why, within each continent, were there so many variations? One rhea might have been sufficient in South America—yet there were two distinct species, living in adjacent regions.
As Darwin would later come to realize, if the two species had arisen from a single common ancestor, it would make sense for them to live close together. When Darwin returned to England and began to examine the origin of species in earnest, the distribution of species would provide some of his more persuasive evidence. The pattern of geographic separation he observed was exactly what one would predict if new species evolved from existing ones.
Two of a Kind
While exploring the hot, dry “devil’s country” near Bahia Blanca, on the coast of Patagonia, Darwin roamed for days on horseback with local cowboys, or gauchos. With spurs clanking and daggers at their waists, the gauchos smoked, drank and ate whatever they could shoot. A popular meal was the greater rhea, a large, flightless bird Darwin compared to an ostrich. But the gauchos also told Darwin of a second, smaller rhea, which turned out to be not just a smaller variety, but a distinct species, with different coloring, shorter, more feathery legs and blue-tinted eggs.
Darwin was anxious to find this lesser rhea, particularly since a rival French naturalist was searching for it as well. But only after the Beagle sailed several hundred miles down the coast did he finally find one. He later learned that that the lesser rhea lived primarily south of the Rio Negro, and the greater rhea to the north. Why, Darwin wondered, did two such similar species live in neighboring regions? Why was there more than one rhea? In the months and years to come, Darwin eventually would ask himself: could the two rheas perhaps have originated from a common ancestor?
Harder Than It Looks
Darwin was impressed by how the gauchos hunted rhea by throwing bolas—two balls connected by a cord:
“The Gauchos pursued at a reckless pace, twisting their horses about with the most admirable command, and each man whirling the balls round his head. At length the foremost threw them, revolving through the air: in an instant the ostrich rolled over and over, its legs fairly lashed together by the thong.”
When Darwin tried to do the same, however, he ended up entangling the legs of his own horse.
“The Gauchos roared with laughter; they cried they had seen every sort of animal caught, but had never before seen a man caught by himself.”
A Christmas Surprise
After leaving Bahia Blanca, where Darwin hunted greater rheas with the gauchos, the Beagle sailed south for 17 days. The next stop was Port Desire, about 700 miles down the coast. A few days after Christmas, Conrad Martens, the ship’s artist, shot a rhea for dinner. It was rather small, but Darwin assumed it was just a young greater rhea. Halfway through the feast, Darwin realized his mistake: the elusive lesser rhea he had been searching for was sitting half-eaten on his plate.
“It was cooked and eaten before my memory returned. Fortunately the head, neck, legs, wings, many of the larger feathers, and a large part of the skin, had been preserved. From these a very nearly perfect specimen has been put together.”
Evidence for Evolution: Island Species
The strange plants and animals of the Galápagos Islands puzzled Darwin. Many lived only on the Galápagos—and sometimes only on one specific island. How had these species gotten there? And why weren’t they the same as those on similar islands around the world?
Instead, in countless details, they were more like species from the mainland of South America. That would make sense if they were migrants. But while many birds, plants, insects, reptiles, and even mollusks on the Galápagos resembled South American species, they were also slightly different.
Before the Beagle reached home, Darwin began to wonder if species from the mainland had reached the Galápagos, and then changed—as they adapted to this new environment. Was it possible? Over time, could species change?
Different On Each Island
Of all the unusual creatures on the Galápagos Islands, the most impressive are the huge Galápagos tortoises. They were once so plentiful that ships stopped by to load up as many as 700 live animals. Since one tortoise could provide 200 pounds of meat, this living cargo ensured fresh meat for months. Unfortunately, even in Darwin’s day the heavy harvest was taking its toll, and their numbers had already been greatly reduced.
Darwin was startled to discover that each Galápagos island was “inhabited by a different set of beings.” For example, the tortoises on each island were slightly different. Darwin reported that by looking at a tortoise’s shell, the colony’s vice governor “could at once tell from which island any one was brought.”
Go To It, Charlie!
Darwin was fascinated and amused by the “immense” Galápagos tortoises. They were so large that he could not resist climbing on top for a ride.
“I frequently got on their backs, and then giving a few raps on the hinder part of their shells, they would rise up and walk away;-but I found it very difficult to keep my balance”.
Separated by the Sea
Minor differences distinguish the Galápagos tortoises on each island. But there are also two basic types, adapted for different feeding habits.
Tortoises from Pinzón (formerly Duncan Island) are “saddle-backed,” meaning that their shells rise in the front, like a saddle. This adaptation makes it easier for them to lift their necks and feed on taller cactus.
Tortoises from Santa Cruz (formerly Indefatigable Island) have “dome-shaped” shells. Animals with these shells live on islands where most of the vegetation is close to the ground, making it unnecessary to raise their heads to feed.
On the Galápagos, Darwin found plants that were related to daisies and sunflowers—but grew to the size of trees. Like the marine iguanas, these island residents seemed to have adapted to their environment: with plenty of sun and little competition, daisies and cactuses could grow to the size of trees.
Darwin noticed another “truly wonderful fact” about these giant daisy relatives. He had found six species, now classified in the genus Scalesia, and remarkably, “not one of these six species grows on any two islands.” It was not enough that they were found only on the Galápagos—each species was found on only one island. The same was true of dozens of other plants. What could account for this diversity?
Birds of a Feather
Darwin was intrigued that almost all the birds on the Galápagos resembled birds from the mainland. The chief difference was in their coloring. Most tropical birds have bright plumage, but on the grim Galápagos islands, the birds were “generally more dusky colored.” Like the iguanas, they seemed to have adapted to match the dark lava around them.
A rare exception was the brightly colored vermilion flycatcher. Perhaps it was not a true Galápagos bird, Darwin thought: “It is worthy of remark, that the only land-bird with bright colours, is that species of tyrant-flycatcher, which seems to be a wanderer from the continent.” It appeared that only species found solely on the Galápagos were colored to match its lava backdrop.
Though it is related to the 35 other cormorant species around the world, the flightless cormorant lives only the Galápagos Islands. And while all other cormorants can fly, this one cannot. Its wings are, however, perfectly suited to swimming—much more useful than flying when searching for octopus, its favorite food.
Before humans arrived on the Galápagos, the cormorant had no natural predators, so it had no need to fly. It was wonderfully adapted to its isolated environment. But when people came, bringing dogs, cats and pigs with them, the defenseless birds were at their mercy. Their numbers have dropped dramatically, and now they are rare.
When most people think of penguins, they think of Antarctica, where these flightless seabirds waddle over the ice and dive for fish and krill. But some penguins live on the coast of South America, thanks to a cold, north-flowing ocean current, and one tiny penguin lives in the tropics. Instead of huddling for warmth, it must battle the blazing heat of the sunbaked Galápagos Islands.
The Galápagos penguin is not only the smallest penguin, and the only one found near the equator, but it is probably the only penguin that has to hold its wings outstretched over its webbed feet to prevent sunburn. Once again, Darwin had found an example of a unique species that lived only in the Galápagos, but which seemed to be a modified version of a species from somewhere else—as if it had somehow become specially adapted to its island environment.
Shortly after leaving the Galápagos, Darwin noticed for the first time that the mockingbirds he had collected from different islands were not all alike. He would later find examples of birds that differed even more from island to island, such as the Galápagos finches, but it was the mockingbirds that “first thoroughly aroused” Darwin’s attention to the peculiar distribution of species on the Galápagos.
A Lost Opportunity
Darwin’s plant collections were all clearly marked and documented, as Henslow had taught him. But Darwin did not always record the exact island where he found each Galápagos bird.
“It never occurred to me, that the productions of islands only a few miles apart, and placed under the same physical conditions, would be dissimilar.”
Too late, he realized that many organisms were unique to each island-a fact confirmed by his mockingbird specimens. Darwin sorely regretted the lost opportunity to do a systematic study of each island, writing,
“It is the fate of every voyager, when he has just discovered what object in any place is more particularly worthy of his attention, to be hurried from it.”
Solving a Mystery
Many corals form rocky reefs that rise from hundreds of feet beneath the sea. Before Darwin, how these large reefs formed remained a mystery. The animals that build coral reefs live only near the sunlit surface. They cannot survive in the dark water at the base of the reef—making it impossible to build a large reef from the bottom up. But clearly they could not build from the top down! So how did they do it? Ironically, the answer occurred to Darwin while he was thinking about the rise of the Andes Mountains.
If land could slowly rise over millions of years, as geologist Charles Lyell argued, it could also sink. Suppose a coral reef was growing in shallow water. What if the sea floor began to sink? The reef would grow upward to stay near the sunny surface. The more the sea floor lowered, the taller the reef would grow. Eventually, a huge reef would form, with the bottom anchored in the dark depths—even though the entire reef was built by animals living near the surface.
Reaching for the Sun
Coral reefs are made by living animals. The main reef-builders are colonies of tiny coral polyps, which secrete layer after layer of limestone. Over many years, this limestone can form an immense reef.
Reef-building corals live only in clear, shallow water, because their bodies contain living, photosynthetic algae that need light to grow. The coral cannot survive without these algae. So like plants spreading their leaves, they grow up and out to capture more sunlight.
An Idea Takes Hold
Near the end of his voyage, Darwin pored over his notes and began to compile them. In a set of notes on birds, written while still on the Beagle, Darwin first began speculating about evolution in writing.
Darwin wondered: Were the different mockingbirds he had seen in the Galápagos just varieties of one species, or were they distinct species? Or might they even be varieties on the way to becoming different species? It would take years of thinking about the idea of evolution, and a great deal more evidence, for Darwin to convince himself his suspicions were correct. But once raised, the question would not go away. Could species evolve?
First Notes on Evolution
Document: Charles Darwin’s “Ornithological Notes”
Date: June 1836; Page: 74 of 85
The Syndics of Cambridge University Library
Pondering the Galápagos mockingbirds raised troubling questions for Darwin about the very nature of species. At first Darwin suspected that all the different mockingbirds were just varieties of a single species. Later he speculated on whether these varieties might represent the early stages of the appearance of new species. In the Ornithological Notes, Darwin writes,
“When I see these islands in sight of each other…tenanted by these birds, but slightly differing in structure & filling the same place in Nature, I must suspect they are only varieties.”
But what if some time ago a single mockingbird species had migrated from the mainland, spread through the archipelago, and then begun to vary on the different islands? What if these varieties grew to be so different that they actually became separate species-that is, they could no longer breed together? The implications were enormous. As Darwin wrote,
“If there is the slightest foundation for these remarks the zoology of Archipelagoes-will be well worth examining; for such facts [would] undermine the stability of Species.”
If species were not stable, but could give rise to new species, everything in natural history would be seen in a new light.”
A New Perspective
At the beginning of his voyage, Darwin saw animals like the green iguana as unique marvels. But by the end, he was looking at species in a different way: He was becoming interested in how species might be related to one another.
Green iguanas were common on the mainland, but they were absent on the Galápagos; instead these islands had their own unique species. Why? Where had these species come from? Eventually Darwin would wonder: Could species from the mainland have reached the Galápagos and somehow changed into the species he found there?
An Island Relative
The Galápagos is not the only place where new species have arisen on isolated islands. If Darwin had visited the Caribbean, for example, he would have found another intriguing iguana to ponder.
The lesser Antilles iguana looks very similar to its larger relative, the green iguana, but it has no tail bars. Once its ancestors became separated from the mainland, it became a distinct species. Yet unlike the Galápagos, where iguanas had to adapt to a rocky, volcanic environment, the forests of the Antilles were similar to the mainland, so fewer new adaptations evolved there.
Within months of stepping off the deck of the Beagle, Darwin settled in London, the nerve center of Britain. Now on fire with the ambition to join the “real naturalists,” Darwin plunged into the work of writing up his Beagle research. Meanwhile, a huge idea was taking shape in his mind. Had those first shipboard insights been right? Could new species arise from old? If they could, how did it happen?
Darwin’s London years were intensely, feverishly creative. Here he would make a name for himself in science. Here he would marry and have his first two children. And here he would begin another voyage—this one inside his mind. It was in London that Darwin brilliantly put together the pieces of his theory of evolution by natural selection. And then, within just five years, he abandoned the smoky city for his beloved English countryside—still keeping his revolutionary thinking largely to himself.
A Man to Watch
Darwin was something of a scientific celebrity when he got back to England. The strange fossils and unfamiliar animals he had shipped home gained him entry into London’s learned circles. Mere months after he left the Beagle, Darwin presented his first paper—on the uplift of the Andes—at the Geological Society.
Determined to earn the respect of the men he called the “great guns,” Darwin threw himself into work. Sorting his Beagle specimens and arranging for experts to analyze them were his first priority. What these authorities told him about his specimens—particularly the fossils and the birds—would profoundly affect his developing theories.
Darwin never claimed to be a botanist. “I knew no more about the plants I had collected than the Man in the Moon,” he wrote his old Cambridge mentor, John Henslow—humorously overstating his ignorance, as he often did. In fact, Henslow had taught him well, and Darwin was a very systematic plant collector. He plucked, pressed and brought back to England a specimen of every species he found in flower on the Galápagos.
Darwin suspected that many of his specimens were “peculiar” to the Galápagos—that is, existed nowhere else—and he was anxious for Henslow’s analysis. Close study of the plants might have provided a clue that they were related to those on the mainland and that their differences were a product of geographic isolation. But Henslow was absorbed in the responsibilities of his family and his country parish—and despite Darwin’s pleas, Henslow studied very few Galápagos plants.
Darwin’s Galápagos birds told an amazing story—but it was one Darwin fully understood only when he heard it from the experts. For instance, Darwin was stunned to learn, back in London, that a group of Galápagos specimens he had thought included many different birds were actually all finches. They were just finches that looked remarkably different from one another—almost as if, he would later write, “one species had been taken and modified for different ends.” And there was more news. Ornithologist James Gould told Darwin that he had brought home three entirely new species of mockingbird, two of the three confined to different islands.
Darwin quickly saw what this meant for evolution. Did islands—and isolation—somehow give rise to new species? Had all these diverse-looking finches, and these species of mockingbirds, diversified from South American ancestors? Darwin hadn’t kept track of where he collected each finch, so although he hastily got finches from other Beagle crewmembers and gave them to Gould, the finch evidence remained shaky. Still, the birds were part of an evolutionary puzzle beginning to fall into place. Seeing this kind of variation among birds of the same kind made Darwin question the idea that species are fixed and unchanging.
Darwin Wonders About Rheas
Unaware that the Rhea pennata already had a name, bird expert John Gould named this rare South American ostrich Rhea darwinii in honor of its collector. Gould’s confirmation that the lesser rhea was indeed a distinct species fueled the fire of Darwin’s curiosity. Darwin knew a larger rhea was common in an adjacent region: were the two derived from a common ancestor?
The skull of an enormous extinct mammal called Toxodon was one of the many spectacular fossils Darwin sent home from South America. Some boys in a remote village in Uruguay had used the skull for target practice and knocked a tooth out with a stone. Darwin bought it from them and was pleased to find a “perfect tooth, which exactly fitted one of the sockets in this skull,” 200 miles away.
This particular animal belongs to a group without modern descendants, but many of Darwin’s fossils seemed to be huge variants of the same general kind of animal he had seen roaming the landscape during his explorations. This led him to wonder if the fossils might be evidence of ancestral forms. In later years Darwin would write that the South American fossils were essential to the “origin of all my views.”
Darwin Wonders about Fossils
Paleontologist Richard Owen analyzed the fossil mammals from the Beagle voyage. A life-sized lithograph of the Toxodon skull by artist George Scharf was part of the Zoology of the Voyage of H.M.S. Beagle, edited by Darwin. In it the young naturalist described the habitats and behaviors of the living species he had collected, and the localities from which his fossils had come.
This book was only part of Darwin’s scientific output during the London years. He also wrote a treatise on coral reef formation and the wildly popular Journal of Researches, based on his shipboard journals.
Darwin relied on his notebooks. In them, he jotted private ideas, questions and fragments of conversations related to his thinking on “transmutation”—what we now call “evolution.” The notebooks reveal a great mind homing in on a great idea: plants and animals are not fixed and unchanging. Instead, all species are related through common ancestry, and they change over time.
Once Darwin started thinking seriously about evolution, he grasped its essentials with astonishing speed. Only a month or so elapsed between the time he opened the first full transmutation notebook, in about July 1837, and the time he drew a crude—but unmistakable—evolutionary tree. This drawing, with the most ancient forms at the bottom and their descendants branching off irregularly along the trunk, reveals that Darwin understood all plants and animals are related. Above his tree Darwin wrote firmly, “I think.”
Darwin’s Evidence: Structure
Limbs that look very different and serve different functions—“the hand to clasp, the bat’s wing to fly . . . the porpoise to swim” —are often much alike in skeletal design. For Darwin, this resemblance was further evidence that large classes of organisms, such as mammals, shared a common ancestry. Each of the bones in a bat wing, for example, has a counterpart in the bones of a human hand.
A Wife, That Most interesting Specimen
After a year or so in London, the 29-year-old Darwin began to think seriously about marrying. But like many an ambitious scientist, he was torn between determination to make a mark and desire to have a family. Would supporting a wife and children mean abandoning his scientific career? A methodical man, Darwin drew up a list of the pros and cons of marriage—and what he called the “nice wife on a sofa” won out. He soon proposed to a woman he had known since childhood, first cousin Emma Wedgwood. Both parties—and both families—agreed it would be the perfect match.
The prediction turned out to be true. Bonds of real affection linked Emma and Charles throughout their long lives, and they would establish a warm, lively and loving family. Yet two troubling issues surfaced in those early years. Darwin’s growing skepticism about religion caused Emma great pain, which in turn caused her husband deep sadness. And Darwin began to suffer increasingly severe and mysterious bouts of illness that would plague his entire working life.
TO WED OR NOT TO WED?
List made by Charles Darwin
July 1838 – Page 1 and 2 of 3
By the time Darwin drew up a list of the pros and cons of marriage, his father had assured him of a generous living allowance. Still, the issue of freedom to work dominated Darwin’s internal debate. Was he willing to give up the “conversation of clever men at clubs,” or risk being forced into a time-consuming and frivolous social life? Could he tolerate “less money for books”? A negative even slips in, unnoticed, among the positives: “terrible loss of time.”
Darwin may not have had a candidate in mind when he wrote this list, but Emma was a logical choice. The Darwins and Wedgwoods were linked by several generations of matrimony, and Emma was the only Wedgwood daughter of marriageable age.
“Children-(if it Please God)—Constant companion, (& friend in old age) who will feel interested in one,—object to be beloved and played with.-better than a dog anyhow.—Home, & someone to take care of house-charms of music and female chit-chat.—These things good for one’s health.-but terrible loss of time.—.”
“TEARS OF JOY”
Letter from Emma Wedgwood to Jesse Sisimondi
November 15, 1838
The brief courtship of Emma and Charles had nearly enough twists and turns to qualify as romantic comedy. “I knew how much I liked him,” says Emma in a letter to her favorite aunt, written four days after her engagement. But Charles was “so fond of Maer and all of us” that she assumed he thought of her as just another cousin.
Charles finally summoned the nerve to propose, but the effort left him with such a headache—and left Emma so startled by the unexpected question—that “we both looked very dismal.” So dismal did they look, in fact, that several aunts went to bed assuming the proposal had somehow misfired. But all turned out well in the end. When the couple spoke to Emma’s father—the same “Uncle Jos” who had argued in favor of Charles’ Beagle voyage-he wept “tears of joy.”
Emma’s letter tells her aunt of her fiancé’s many virtues:
“He is the most open, transparent man I ever saw, and every word expresses his real thoughts. He is particularly affectionate . . . and possesses some minor qualities that add particularly to one’s happiness, such as not being fastidious, and being humane to animals.”
“MY OWN DEAR FUTURE WIFE”
Letter from Charles Darwin to Emma Wedgwood
January 20, 1839 – Page 3 of 4
Charles was by turns charming, boyish and thoughtful during his three-month engagement. In high spirits, he wrote a letter to Emma describing his adventures on the train to London from Emma’s home at Maer, the arrival of a curious wedding present—which turned out to be asparagus tongs—and a shopping spree to buy odds and ends for the house Charles had rented for the couple in London.
He then turns serious, and after confessing that his solitary time on the Beagle was “the commencement of my real life,” he confides his hopes for a future life with Emma:
“I think you will humanize me, & soon teach me there is greater happiness, than building theories, & accumulating facts in silence & solitude. My own dearest Emma, I earnestly pray, you may never regret the great, & I will add very good, deed, you are to perform on the Tuesday: my own dear future wife, God bless you.”
“EVERY THING THAT CONCERNS YOU CONCERNS ME”
Letter from Emma Darwin to Charles Darwin
February 1839 – Page 2 of 4
Dr. Darwin had advised Charles to keep his spiritual doubts to himself—“some women suffered miserably” if they thought their husbands were not going to heaven, he told his son. But a letter that Emma wrote soon after their marriage shows Charles must have ignored his father’s advice.
Emma took a much more literal view of resurrection and salvation than did her husband. She believed Charles tended to apply scientific standards of proof to questions of faith, and—as revealed in her letter—his skepticism worried her deeply.
“May not the habit in scientific pursuits of believing nothing till it is proved, influence your mind too much in other things which cannot be proved in the same way, & which if true are likely to be above our comprehension.”
At the bottom of this letter is a poignant note in Darwin’s hand. “When I am dead, know that many times, I have kissed & cryed over this. C. D.”
Darwin knew that starlings looked like other starlings, of course, and moles like other moles. And Darwin also knew that within a nest or a litter, no two individuals look exactly alike. But Darwin, unlike anyone else, was absorbed in thinking about evolution, and he started to wonder about the small differences between individuals of the same kind. Why did they exist? Could they be useful?
A country gentleman by birth, Charles knew a lot about domesticated animals. He was aware that people often bred animals with desirable traits, and that over time such breeding exaggerated small differences. Horses were horses, but one bred for hunting looked very different from one bred to pull heavy loads. Dogs were dogs, but a tiny lap dog and a large, lean greyhound looked nothing alike. Somehow, Darwin thought, variation is the key to understanding how species change.
A Theory by Which to Work
Darwin always read widely, on the lookout for new ideas. In late September 1838 he found himself reading—“for amusement,” he later recalled—the “Essay on Population” by political economist Reverend Thomas Malthus. In this essay, Malthus argued that human population could quickly outstrip the food supply: competition for food or space was a constant force keeping population in check.
Darwin immediately saw how the idea could be applied to the natural world. More animals were born than could survive. They constantly struggled against one another for food or room to grow, he thought. That meant any plant or animal with a competitive edge—drought tolerance, a thicker-than-average coat—could live longer and leave more offspring than its fellows. The presence of such adaptations controlled, in effect, which individuals would represent the species in the next generation.
Now Darwin could see how variation could make a difference: individuals with useful traits would, on average, survive to reproduce and pass along those traits. “It is a contest, “ he wrote, and “a grain of sand turns the balance.”
The E Notebook is fourth and last in the series of transmutation notebooks. In it Darwin considers such subjects as adaptation—the fit between organisms and their place in nature—and the pace of geological change. Perhaps most important, in this notebook he spells out the theory of natural selection.
“Three principles will account for all
(1) Grandchildren. like. grandfathers
(2) Tendency to small change. . especially with physical change
(3) Great fertility in proportion to support of parents”
Darwin’s last principle refers to Malthusian population pressure. He wrote this entry sometime between late November and early December 1838.
Adding it Up
By the late summer of 1842 Darwin felt ready to commit an outline of his theory to paper. The main points were clear: plants and animals with useful—and heritable—variations were likely to live longer. That meant they could leave more offspring, some of which would carry the new trait. Over time, species could change through this process of “natural selection,” a term Darwin first uses in this outline.
Darwin’s rough sketch of his argument is almost a miniature version of his future masterwork, the Origin of Species. Yet he kept his ideas under wraps for nearly two decades more. Why? For one thing, Darwin wasn’t finished thinking: some critical details were still to come. And he knew he needed to amass a great deal of evidence to convince others of such a radical idea. But equally important, the time wasn’t right. Still establishing his career, Darwin feared the ridicule of respected scientists such as Charles Lyell and Richard Owen. And he knew his ideas would be seen as an attack on religion and established society. It was better to wait.
Putting It All Together
In the summer of 1842, Darwin and his wife Emma spent several months visiting their families in the quiet English countryside. While at Emma’s family estate, Darwin took up a pencil and covered 35 sheets of rough paper with an outline of his theory. This draft, which Darwin revised and expanded until its ideas found a home in the Origin, was for his eyes only.
Darwin wrote in a quick, intense burst: as one of his sons would later write, his outline is “more like a hasty memoranda of what is clear to himself, than material for the convincing of others.”
In this passage Darwin considers the connection between geographic isolation and the formation of species.
“. . .barriers of every kind seem to separate regions in a greater degree than proportionally to the difference of climates on each side. Thus great chains of mountains, spaces of sea between islands and continents, even great rivers and deserts.”
He is emphasizing the importance of physical barriers—“spaces of sea between islands” like the Galápagos—in the origin of new species.
Men and Apes
An orangutan called Jenny was the first ape Darwin ever saw—and one of the first ever to appear in the London Zoo. Zookeepers often enhanced the humanlike qualities of these popular exhibits by dressing the animals in children’s clothes and teaching them human habits. But Darwin would have seen a resemblance between Jenny and his own offspring without the costuming. When Jenny was angry at her keeper, he wrote, the animal “threw itself down on its back & kicked & cryed like a naughty child.—Do monkeys cry?-they whine like children.”
Almost as soon as he started thinking about evolution, Darwin understood this: what applied to plants and animals also applied to people. We had evolved, too. “It is absurd to talk of one animal being higher than another,” he wrote in one notebook; in another, “Monkeys make men.” At a time when most of his fellow citizens took for granted that we had been created in the image of the divine, such thinking was outrageous—the most radical of Darwin’s many radical ideas.
Brothers under the skin
Biologist and teacher Thomas Huxley was known as “Darwin’s bulldog.” The illustration below is from his book on human evolution, published eight years before Darwin’s Descent of Man. A gifted and provocative speaker, Huxley often lectured on evolution with his arm draped affectionately over a gorilla skeleton.
A LIFES`S WORK
But for nearly two decades Darwin kept his secret from the world. It took a letter from the Malay Archipelago—a letter outlining another man’s version of natural selection—to push him into print. Shutting himself in his study, working feverishly, Darwin finally produced the Origin of Species. In 1842 Charles Darwin and his family fled London in search of peace and quiet. They found it in a tiny village 16 miles outside the city, and for the next 40 years their home—called Down House—was Darwin’s retreat, research station and the hub of his vast scientific network. Working in his study, greenhouse and garden, corresponding with scientists around the world, Darwin patiently completed the puzzle of evolution by natural selection.
That book—and its companion volume, the Descent of Man – would spark a revolution. They would also make Darwin the most revered, and controversial, scientist of his time.
“Like Confessing a Murder”
Once settled at Down House, Darwin wrote a fuller version of his theory of evolution by natural selection. Yet he didn’t publish it—why?
There are several reasons. Darwin’s theory was still incomplete; he wanted to think more, gather more evidence. Other writers, with other evolutionary schemes, were being ridiculed, and Darwin was determined to avoid that fate. His own ill health and family tragedy interfered with work. Imagining the reaction of the public and the established church filled him with dread.
Yet gradually, over a decade or so, Darwin began letting a few trusted friends in on the secret. It was “like confessing a murder,” he wrote. But private confession was one thing; telling the world, quite another. Darwin intended to work at his own pace, until his theory was solid enough to satisfy his severest critic—himself.
A Step Closer
This landmark manuscript on evolution by natural selection dates from early 1844. Writing it took Darwin one giant step closer to what he called his “big book on species.” In this essay Darwin tackles the same topics he had covered in his brief outline two years earlier, but the treatment is much fuller. As his son Francis later noted, “In the 1844 Essay there is an air of freedom, as if the author was letting himself go.” Darwin may have felt liberated because he never intended the Essay to be published in his lifetime—and indeed, it wasn’t. But with it, Darwin crossed a threshold: almost all of his major thinking was in place.
In the page on display, Darwin discusses something he saw as a difficulty with his theory. Natural selection depended on variation, but Darwin was having a hard time determining how much variation actually existed in nature.
“Lamarck has observed that, as long as we confine our attention to one limited country, there is seldom much difficulty in deciding what forms to call species and what varieties; and that it is when collections flow in from all parts of the world that naturalists often feel at a loss to decide the limits of variation.”
As the years passed, the sprawling house at Down filled up with children—the Darwins would have ten in all—and a series of governesses, nurses and pets. Charles and his wife Emma were relaxed and affectionate parents whose children, daughter Henrietta later wrote, felt like “creatures whose opinions and thoughts were important.”
Since London days Darwin’s health had been fragile. Breaks in the regular routine—even an interesting talk with a visitor—could provoke spells of vomiting and dizziness. But he doggedly pursued his research program, and on some days his work could be an exciting household adventure. Children tracked the flight paths of bumblebees, a governess joined in counting the plant species in a meadow, a longtime servant helped Darwin boil carcasses of small mice and birds to “skeletonise” them for study.
Yet Down House was full of ordinary life as well. Family friend Joseph Hooker recalled “long walks, romps with the children on hands and knees, and music that haunts me still.”
Father And Son
Above is the only known daguerreotype of Darwin with a family member. Done in 1842, it shows Darwin with his first son, William. In the mid-1800s boys often wore dresses until the age of four or five.
When Darwin looked at the expressions on people’s faces—and at the body language of dogs and cats—he saw evidence for evolution. These pictures, some posed and some candid, appeared in his Expression of the Emotions in Man and Animals (1872). What Darwin himself observed, and what he learned from scientists studying cultures worldwide, convinced him that all humans have the same feelings. What’s more, they show them on their faces in similar ways.
Similarly, Darwin thought, animals had recognizable emotions. Chimpanzees could feel disappointment. When they were disappointed, they sulked; and when they sulked, they stuck out their lips like pouting children. Experts of the time believed, wrongly, that we humans had special muscles in our faces so we could express what they called our “exquisite feelings.” Darwin’s work contradicts this. Our emotions, and the way we express them, connect us with the rest of life on Earth.
From Pigeons to Potatoes
All the research Darwin undertook in 40 years at Down revolved around a single grand theme: evolution by natural selection. In at least 16 books and many papers, Darwin explored variation and adaptation. He worked tirelessly to figure out how natural selection had acted on variation to produce the marvelous adaptations he saw.
But in many cases he couldn’t do this directly. Extended studies of wild nature—measuring and tracking minute changes in fur, feather or flower over generations—were unimagined by any naturalist of the period. So instead Darwin often turned to domesticated species—manageable and well-documented groups that he, or the experts he knew, could breed and shape. Pigeons, rabbits, cabbages, gooseberries—these would be a major object of study and his window into the workings of selection.
Charles Darwin, Pigeon Fancier
The birds on display are all types of fancy pigeons Darwin raised at Down House. Raising the animals—all these breeds are descended from the rock dove—was a popular hobby of the day. Breeders competed to produce varieties with a particular color or beak shape, and Darwin did the same. At one point his flock grew to 90 birds.
But Darwin was interested in evolution, not pigeon shows. He wanted a sense of how much variation existed within a single type of animal in nature. Breeding animals—selecting and perpetuating desired traits—was a sped-up version of the process that gave rise to new species in nature, he thought. Much more than a hobby, Darwin’s pigeon work was a way to demonstrate how dramatic the effects of selection could be.
A Special Group
“Believing that it is always best to study some special group, I have . . . taken up domestic pigeons,” Darwin wrote. There are about 200 named breeds; those Darwin raised provided him insight into the workings of selection.
Plant a Cabbage, Get a Brussels Sprout?
Variability in the cabbage family interested Darwin. The wild cabbage, he knew, had given rise to very different-looking varieties, including Brussels sprouts, broccoli and kale. What accounted for this diversity? “The explanation is obvious,” Darwin wrote. Because we humans eat the leaves of these plants, farmers had been selecting the “many useful variations in their leaves and stems” since prehistoric times. Such strong selective pressure produced those distinct shapes.
Birds of a Feather
Darwin was always ready to learn from experts, both amateurs and scientists. He belonged to several workingman’s pigeon clubs as well as the exclusive Philoperisteron Club, whose members were voted in.
More Than Skin Deep
Darwin included these diagrams of pigeon skulls in his major work on domestication. The color, shape and placement of feathers are the obvious markers of pigeon breeds, but the skeletons underneath differ, too. Had these skulls belonged to wild birds, Darwin thought, they would be considered different species. And if artificial selection could produce such diversity over decades, what might natural selection produce over millions of years?