If you only remember one name in the entire
history of modern biology, it should be… two names. Because the first biologists were a pair of
freaky intellectual twins, just like Newton and Leibniz. But with more barnacles and monkeys. Let’s meet Charles Darwin and Alfred Russel
Wallace. [INTRO MUSIC PLAYS] In the early 1800s, England was already moving away from the traditional way of thinking
about life, which was then called “natural theology.” In this belief system, the living world was
created by a kindly but hands-off God. And there were four aspects of Creation:
One, there was a divine Creator. But simply believing in God didn’t prevent
you from asking how life works. Two, there were species that didn’t change,
ever. This idea was known as the fixity of species. But keep in mind, the French had already worked
out that species do change over time and go extinct. They just hadn’t figured out how. The third aspect of natural theology was a
short creation, in which the world was only about six thousand years old. But geologists had pushed the age of the earth
back to millions of years. And the fourth idea was the one that was still
contentious in 1800—a perfect design for each species. The idea went: if God made, say, a turtle,
he knew what he was doing. Even if that turtle was stupid or ugly, it
was still a designed-by-God original, and there wasn’t too much sense trying to understand
the mechanism, the how, of that design process. (Note: we here at Crash Course love turtles! There are no stupid ugly turtles!) Today, natural theology is associated with
philosopher William Paley, perhaps because he wrote a book in 1802 called... Natural Theology. This book influenced a young scholar named
Charles Darwin. But wanted to understand the “how.” Young Chuck originally wanted to become a
physician, but he hated the sight of blood. So he went to Cambridge to study beetles but
skipped a lot of lectures. He earned Gentleman’s Cs and graduated at
twenty two with no direction in life, just a huge collection of beetles. Which, to be honest, is more than I had. So Chuck’s family did what any rich family
with a beetle-obsessed son would do: they sent him to South America on a ship with a
cute name: The HMS Beagle. Chuck was seasick the entire five years. But the voyage was more than worth the lost
lunches: it turned Darwin from a mere collector into an extraordinary theorist. For one, the voyage gave Darwin time to read
the geological theories of Charles Lyell and think about gradual change over long ages. Wouldn’t it be nice to like get on a boat
with a couple of books and just think for 5 years, and puke a lot? Near Concepción,
Chile, Darwin saw a volcano and felt an earthquake: he got to live through Lyell’s theory of
how geological changes happen! The voyage also gave him lots of opportunity
to collect and compare fossils. For instance, Darwin found fossils of a species
that looked like a giant sloth, one like a giant capybara, and
one like a giant armadillo. And Darwin thought, what if these giant creatures
did not just coincidentally look like modern animals, like sloths, rodents, and armored
mammals, but were actually ancestors of them? But the main thing the voyage did was give
Chuck access to hundreds of specimens from similar-looking species that lived close to
each other, but in slightly different environments. The most famous examples, of course, come
from the Galapagos Islands off the coast of Ecuador, home to land and marine iguanas,
diverse mockingbirds and thrushes, tortoises by the dozen, and—say it with me—finches! Like beetles before and barnacles later, finches
became an absolute obsession for Chuck. He had to catch them all. Lucky for him, the people who lived near the
Galapagos even explained to him that the different species seemed to vary according to island. This turned out to be one in a number of clues
that would lead Chuck to developing the theory of evolution by natural selection. When he got back to London, Darwin wrote up
his meticulous fieldnotes. He published the Zoology of the Voyage of
HMS Beagle in volumes from 1838 to 1843. This alone made Darwin a serious naturalist. His generous sharing of specimens made him
not only a member of the London scientific world, but a leader in it. He sent specimens to naturalists including
John Gould, who helped Darwin confirm that his finches were actually different species,
and not just varieties of one species. Major clue! And then Darwin read the Essay on the Principle
of Population by a cranky reverend named Thomas Robert Malthus. Malthus argued that population increases geometrically,
but food only increases arithmetically: the logical result must be famine. This was the final clue—a relationship between
the environment and the reproduction of populations. Darwin reasoned that living beings compete
over resources, and only the most fit for a given region survive. It’s as if nature selects them. Hence his choice of the term “natural selection,”
for the primary mechanism of evolution. Compare this to natural theology: there’s
no Creator involved. Species aren’t fixed. The process takes aeons. And design—what design? Useful traits emerge over time. At the same time that he was solving the biggest
problem facing the study of “what is life?”, Darwin was also busy performing Victorian
gentleman-ness: he married his cousin, Emma Wedgwood, in 1839. He had babies and moved to a manor in Kent. He got REALLY into billiards. But, what Darwin was not doing? Publishing a complete theory of evolution. What was Darwin’s next move? Pigeon fancying. He bred pigeons in order to understand artificial
selection, or how humans design organisms. Because breeding pigeons is a lot faster than
watching finches change over millennia. And then? Eight years studying barnacles. He worked on his theory, writing to his friends
for advice about it. But he didn’t publish it. Darwin wanted to wait until he had incontrovertible
proof. Then in 1858, Darwin received a letter from
one Alfred Russel Wallace. Wallace had also discovered natural selection. He sincerely wrote to Darwin for advice: would
he be interested in, uh, an evidence-based theory explaining how organisms evolve? Darwin’s mentor, Lyell, told him that he
had no choice now. So Darwin and Wallace published a joint letter
in the Journal of the Proceedings of the Linnean Society of London. And then Darwin wrote a compelling, five hundred-page
book detailing his theory. In one year. In 1859, On the Origin of Species by Means
of Natural Selection, or just “the Origin,” debuted as a modest edition of twelve hundred
copies but soon became a smash hit. It was a scientific bestseller, intended for
a wide audience. No footnotes! The book explained how “descent with modification”
or “transformism” actually works. In any population of the same species, you
can see a natural variation in traits: some finches have longer beaks; some have shorter
beaks. Over time, small changes in the environment
add up, favoring some traits over others. Natural selection modifies the population:
the fittest survive and reproduce, passing on their traits. Say, the long beaks get to more food and survive
when food becomes scarce. Unfit species die out. Populations diverge into new species! Darwin’s writing, influenced by Malthus,
shifted away from a harmony of nature and toward a competition for resources—a war. But Darwin’s theory wasn’t perfect. In fact, he included a chapter on the “difficulties”
facing natural selection. These included a lack of transitional forms
in the fossil record: how do we get from fish to amphibians? Even more basically, where do variations come
from? How are they passed on from one generation
to the next? We have answers to these questions today—stayed
tuned!—but Darwin didn’t, and he admitted as much. This was… refreshing. He didn’t claim to be a genius. He didn’t bash earlier theories. The Origin didn’t even mention God, much
less where humans come from. Instead, Darwin focused on what he knew: variation
in beetles, finches, pigeons, barnacles, and fossil animals. His theory, backed by so much evidence, accounted
for how new species evolve. Even more importantly, Darwin united many
branches of natural history into a single synthetic theory and proposed a bunch of clear
and important questions for future research. In fact, Origin marks a kind of evolution
of natural history, which was focused on observation and description, into biology, which is more
focused on testing theories about living things. Darwin’s skill as a writer is one reason
his name eclipsed Wallace’s. Another is that my dude was rich! Like, born rich, invested well, married rich… He was doing all right. And Wallace? Introduce him, ThoughtBubble: Al was born to a family with money problems. He quit school at sixteen to work surveying
canals with his brother. And at twenty, he quit surveying to teach. Wallace read Malthus. He also read Darwin’s details of his American
voyage and became a lifelong fan. Wallace met Henry Walter Bates in 1844. They became science besties and decided to
figure out how evolution works in order to apply that knowledge to human society and
save people from greed and individualism. Wallace and Bates went to the Amazon from
1848 to 1852 to collect specimens for museums in London. And he was super successful… until he set
off back to England. His boat, brimming with specimens, caught
fire and sank. Wallace watched from his lifeboat as all of
his hard work—his carefully trapped and cataloged monkeys and his parrots—sank into
the dark waves. He was not rescued for ten days. But, like Galileo after his trial by the Inquisition,
Wallace never gave up. In debt, Wallace decided to continue collecting
more specimens to pay the bills, this time in Southeast Asia in 1854. He sent specimens back regularly, developing
a brilliant reputation. And Wallace was doing a more than collecting:
traveling from island to island across what is now Indonesia, Malaysia, and Singapore,
he observed that different environments seem to produce different populations of organisms…
perhaps even new species. While sick in bed in 1858, Wallace suddenly
recalled the essay on populations by Malthus, and an entire theory clicked into place. In his words: A “self-acting process”
meant that, for any species, “the fittest would survive.” The colleague he thought would most appreciate
this wild new theory? A slightly older naturalist in London… Thanks ThoughtBubble.
After the joint paper with Darwin, Wallace continued working in Southeast Asia until
1862. He published his major work, The Malay Archipelago,
in 1869. Wallace observed that there is a sort of invisible
line—“Wallace’s line”—in Indonesia: to the west, species resemble those in Asia. To the east, they resemble those in Australia. In fact, Wallace invented the discipline of
biogeography, or the study of plants, animals, and geological formations together. So, between them, Darwin and Wallace were
reaching a lot of people with their ideas. And it’s true that some people with conservative
religious values were outraged at the public acceptance of a Creation that had no elegant
design, just random variation. But the reaction to natural selection was
mostly acceptance. Darwin’s writing, and the depth of his and
Wallace’s evidence, settled the matter for many readers. In fact, in some ways, Darwinism was accepted
too easily. Darwinism quickly became equated with the
term “survival of the fittest,” which was coined in 1864 by biologist Herbert Spencer
and appeared in the fifth edition of Origin. This term isn’t a bad summary of natural
selection, in terms of animals and plants. But it was increasingly applied to human society,
as “social Darwinism,” in a way that Darwin and Wallace would not have approved of. An Industrial Revolution has just brought
radical change to England. A new class of capitalists saw themselves
as more “fit” to govern the world than the nobles they replaced or the workers they
controlled. Next time—Darwin’s cousin, Frank Galton,
will try to apply Chuck and Al’s theory to society. Yes, it becomes strange, and even tragic. So be sure to come back. Crash Course History of Science is filmed
in the Dr. Cheryl C. Kinney studio in Missoula, Montana and it’s made with the help of all
this nice people and our animation team is Thought Cafe. Crash Course is a Complexly production. If you wanna keep imagining the world complexly
with us, you can check out some of our other channels like Scishow, Eons, and Sexplanations. And, if you’d like to keep Crash Course
free for everybody, forever, you can support the series at Patreon; a crowdfunding platform
that allows you to support the content you love. Thank you to all of our patrons for making
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