The Making of a Theory: Darwin, Wallace, and Natural Selection — HHMI BioInteractive Video

[Music] after four arduous years of collecting animals in the Amazon jungle Alfred Russell Wallace is finally heading back to [Music] England sailing with him are the rewards of a long journey thousands of specimens he will sell to museums and collectors exhausted from his travels Wallace is looking forward to the Comforts of home [Music] I'm afraid the ship's on fire [Music] [Music] every one of Wallace's specimens is destroyed [Music] his hard-earned records of which animals live where in South America are also lost these notes contain Clues to the question that Wallace risked so much to answer

it was the greatest scientific mystery of his time where do species come from but now Wallace's thoughts must turn to a more urgent concern survival his hands are burned raw from sliding down a [Music] rope his Lifeboat is leaking badly The Castaways have little food or water and are 700 mil from the nearest shore Wallace vows that if he survives he will never sail again [Music] this is the story of the search for the Origin of Species and of the Epic Adventures of the two explorers who found the answer [Music] Alfred Wallace might have avoided

his predicament had someone else not been keeping a secret another British naturalist had already answered the question of the Origin of Species years earlier but he had dared to share his ideas with only a few trusted friends Charles Darwin set sail on his own Voyage 20 years before Wallace's [Music] shipwreck he he was an unlikely revolutionary he lived in a time when most scientists believe that each species was specially created by God in its present form and constant and not somehow the product of natural laws and changeable at the age of 22 Darwin also believed

in special creation he was even planning to become a clergyman but then he got a surprising offer Darwin jumped at the chance to sail around the world on a British Naval vessel the Beagle the offer was more about his pedigree than his resume Darwin could be cheerful upper class company for the captain no small task given that the beagle's previous Captain became despondent and shot himself The lure for Darwin he was a passionate amateur naturalist and now he'd have the chance to see and collect animals plants and rocks around the globe early in the voyage

he examined plankton with his stateof the-art microscope an instrument that only the son of a wealthy family could have [Music] afforded Darwin was perplexed why was there so so much Beauty in the middle of the ocean where no one was around to enjoy it why were these forms created for so little a parent purpose but for every moment of Joy or Discovery Darwin experienced a hundred of suffering he was often seasick not merely Que but desperately violently ill his Adventure came at a high [Music] [Music] price Darwin's curiosity was not limited to science on the

coast of Argentina he sampled a local delicacy roast armadillo he thought it tasted like Duck not far from this barbecue Darwin found an interesting fossil it was a small piece of an extinct creature called glyptodon it was part of its protective covering Darwin had seen a similar bony shell on the armadillo he had just eaten but this fossil came from a giant the animal he discovered would have been dinner for a thousand Darwin found several more fossils nearby including ground sloths like this one they were all enormous compared to living species Darwin would Ponder the

GE logical relationship between the extinct and the living Darwin didn't yet understand why fossil of extinct animals turn up where similar animals live [Music] today after nearly 4 years at Sea twice as long as Darwin had signed up for the Beagle arrived in a remote Spanish colony the Galapagos it would have been the dream of most any naturalist to explore these [Music] [Music] islands but when Darwin arrived he was more exhausted than excited if hell had a garden he thought this is what it would look [Music] like the black volcanic rocks felt as if they'd

been baked in an oven the plants stank he didn't see a single beautiful flower the Darwin that arrived here was not the great theorist that we know today he was a 26-year-old collector collecting really almost at random any kind of plants any kind of animals any kind of rocks he didn't even know the meaning of what he was collecting until much [Music] later he thought the island seagoing iguanas look dimwitted and hideous but he did like a different galpagos reptile the tortoises he even took a ride on one you magnificent Beast [Music] when Darwin was

here in the Galapagos he was given an important clue the Spaniard told him that they could tell which island of ttis came from just from the shape of its [Music] shell why would tortoises on nearby Islands look so different from one another the Island's mocking birds also caught Darwin's attention he focused on their subtle [Music] differences one kind of Mocking Bird had smudges on its breast another had a large dark patch under each eye a third had a pure white [Music] breast Darwin was astonished when he realized that just like the tortoise each kind of

Mocking Bird lived on a different Island so even though he stayed here just 5 weeks out of the whole fiveyear Voyage is what he saw here in these five weeks that left the greatest impression on Darwin and would lead him to his greatest ideas after stops in Australia and Africa and as the Beagle turned home to England Darwin had the chance to reflect on what he'd been seeing in his cabin Darwin puzzled over the galpagos animals it was remarkable that similar but distinct creatures lived on such nearby [Music] Islands what would explain this fact according

to special creation God made a different species for each island but another possibility occurred to Darwin perhaps one species might have come from the mainland and then changed in different ways on different Islands the galpagos animalss were raising a radical idea species might change after Darwin returned to England he starts thinking about everything he saw on this 5-year voyage and he's sticking back to the geology the fossils the animals that he'd seen he's in this process he calls mental rioting just letting every thought stream to him until finally he has his big idea rioting was

the right word his ideas were doing violence to the established [Music] order the best explanation for what Darwin saw in the galpagos was that species changed into new species over time one kind of Mockingbird somehow became three tortoises multiplied into different forms and what did it mean that armadillos and sloth live today were extinct giant versions once roamed maybe Darwin thought today's species are descended from older extinct types if so then all species are connected to one another in a family tree it is a simple crude sketch but Darwin's drawing is a radical new picture

of Life any species can give rise to new and slightly different species as Generations pass Grand species arise and then great grand [Music] species Darwin's bold idea was that species come from other species just as naturally as children come from parents there was a word for this kind of [Music] thinking [Music] heresy so the Origin of Species was natural not Divine it was a revolutionary idea that overthrew special creation it ran against Church teachings and what most Europeans believed including most scientists still a young man Darwin couldn't reveal his great idea he would be attacked

and [Music] ruined many years later Darwin's popular account of his voyage is a big success he's published six books and has become England's most prominent naturalist [Music] but he is still keeping his biggest idea [Music] secret Darwin is gathering yet more evidence for his theory when at a museum Al W he encounters an Earnest young man I've read your work Voyage with the Beagle it is excellent inspiring thank you very much Wallace had survived his ordeal at Sea to do some research after 10 miserable days in a Lifeboat he had been rescued by a passing

ship bothast to my notes before I leave ah Wallace and Darwin are meeting for the first time the two explorers share a great passion for nature but they are in very different situations I'm headed to the Malay archipelago to do some research oh excellent I'm Wallace is single he has to collect for a living and he has yet to make his Mark yeah so no have I've never been there are you are you collecting what yes I'm Darwin is married and has a family he is financially well off and has a scientific reputation to protect

Wallace is as open as Darwin is secretive about his interest in the Origin of Species Museum and I'm very interested little does Darwin know that this young man will soon Force his hand I could send you back some specimens if you'd like oh very much so yes uh thank you but please no Barnacles I've just finished a work on bonac coret and Wallace doesn't have a clue that Darwin has already scooped him um have you written anything yourself believing that the question of the Origin of Species is still wide open and despite having nearly lost

his life at Sea Wallace sets out on a new voyage he travels to the region between the Pacific and Indian oceans the Malay archipelago for the next 8 years he will collect and study animals as he hops from Island to Island in a 14,000 mile Journey [Applause] Wallace is captivated by butterflies his favorite group is called bird wings after their shape and large [Music] size they command a high price for their striking colors [Music] [Music] he finds Birdwing butterflies throughout the archipelago he identifies new species some that are slightly different from those on nearby Islands

the melee butterflies suggest to Wallace what the Galapagos animals revealed to Darwin species change but Wallace too seeks to understand the bigger picture having explored jungles on opposite sides of the globe he can compare where different groups of animals live and ask why they are found where they [Music] are Wallace The Collector now becomes Wallace the theorist bird wings occur near other species of bird wings in the melee archipelago across the globe in the Amazon live different families of butterflies bird families also cluster geographically katus live only in the melee archipelago and Australia whereas the

Americas are home to maau and hummingbirds around the globe the more similar two species are the closer they tend to live why is this so Wallace formulates a new law of nature it's about where new species arise they don't appear in random places they arise near similar species he realizes the profound implic a that species are connected to one another like the branches of a tree on his own Wallace arrives at Darwin's still secret Tree of [Music] Life Wallace finds more evidence that all species are related by considering some intriguing creatures manatees are mammals that

live entirely in the [Music] sea but inside their flippers are finger bones similar apparently useless bones are inside whale flippers too if God had created these animals from scratch wouldn't he have skip the fingers imperfections such as these vestigal structures make it clear that every species is a modified form of an older species zigzagging across the Malay archipelago Wallace gathers critical evidence for his law on the island of Borneo he sees monkeys and orangutans but elsewhere in the archipelago in New Guinea the mammals are strikingly different No Monkeys here instead up in the branches are

tree kangaroos are supul whose young grow up in [Music] pouches Island by Island Wallace notes which of the two groups of mammals lives there those with pouches and those without animals on the Eastern Islands resemble those of Australia animals to the West those of Asia it's as if a line splits The Arc of pelo it will be dubbed The Wallace Line why would God draw a boundary through these islands and put monkeys in the trees on one side and put kangaroos in the trees on the other side this made no sense special creation couldn't explain

the line but Wallace's earlier law could that species come from pre-existing nearby species the Eastern islands of the Malay archipelago Wallace surmised were once connected by land to New Guinea and Australia so animals like kangaroos could hop on [Music] over the Western Islands were never connected to the Eastern ones but they were connected to Asia so the West had different mammals ones with placentas instead of pouches it's the history of the planet not special creation that explains the distribution of species in Wallace's time geologists understood that natural processes such as volcanism and erosion could change

the shape of islands and continents but what about species how do they change that is Wallace's next [Music] question as a collector he has a great eye for detail as he chooses specimens to sell to his [Music] customers he knows that among all living things from butterflies to snails individuals within a given species usually vary in small ways but what does that variation have to do with how species [Music] change the answer comes to Wallace during a high fever he must have been thinking about the very real chance that he would die he recalled the

English Economist Thomas malus who noted that human populations are held in check by famine disease and death Wallace realized that was even more the case in nature without death any species would quickly overrun Earth but animal populations tend to Hold Steady that's because huge numbers of Young die every generation two facts now snap together massive death plus [Music] variation Wallace now sees how species could change [Music] those individuals with variations that give them even a slight Edge Will Survive reproduce and in time outnumber those without the advantage his is a fundamentally new picture of nature

of intense even violent competition [Music] Wallace thinks he might have an important new idea but he wants a second opinion before [Music] publishing he knows just the right person to ask thousands of miles away in England [Music] excuse me sir this just came for you ah yes thank you [Music] [Music] Darwin is shocked he couldn't have written a better summary of his own theory of how species change he called it natural selection than what had just arrived from Wallace how could this happen both men had observed slightly different species on nearby Islands and concluded that

species could change over time both had collected huge numbers of specimens and realized that individuals vary within species and both had witnessed nature up close and realized it was a battlefield with massive casualties same fact patterns same explanation great minds think alike Darwin now worries that he will lose all the credit for his original idea Darwin turned Wallace's manuscript over to two close colleagues who have been privy to Darwin's ideas on natural selection they decided that Wallace's manuscript and some excerpts from Darwin should be read aloud together on the same day in London the idea

was to share the credit although everyone involved including Wallace agreed that Darwin got there first Darwin published his own masterful full length account in 1859 On the Origin of Species became one of the most influential books ever published it was an instant Sensation that signaled the birth of Modern Biology Wallace eventually wrote a book on Evolution he gave it the title Darwinism Darwin and Wallace who framed a new view of Life driven by competition did not compete themselves instead they became lifelong friends Bound by their shared hard-earned insight into how Evolution shaped the living world

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