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  • By the end of World War Two and the beginning of the Cold War, physics had been revolutionizedagain.

  • Much as Newton had done in 1666, Einstein did in 1905.

  • But once again, biology was late to the paradigm-shifting party.

  • Remember how Darwin and Mendel lived around the same time, but everyone forgot about Mendel

  • until 1900, and even then biologists saw Darwinism and Mendelism as two competing grand theories

  • about how life works?

  • The Darwin and Wallace people thought traits were blended, and they studied big populations

  • of different species, in the wild and in fossils. While the Mendelians studied roses or flies

  • in labs.

  • And they saw that some traits aren't blended, but jump around according to Mendel's laws.

  • And, meanwhile, the eugenicists studied variation in human populations, for creepy reasons.

  • Well, it's time to bring these threads together into a new paradigm for biologyone that

  • accounts for change over time in species through exacting quantitative analysis on different

  • real-world populations.

  • [Intro Music Plays]

  • Medicine changed a lot after 1900 due to the discovery of different therapies like antibiotics.

  • Likewise, biology changed a lot as scientists combined different ideas, from natural selection

  • to statistics, in new ways.

  • The result is a framework called the Modern Synthesis, orneo-Darwinism.” And even

  • today, biologists mostly work within it.

  • Basically, the Modern Synthesis uses Mendelian inheritanceMendel's rulesto explain

  • how Darwinian natural selection works in real time.

  • So Darwin and Wallace's big ideas about change over long epochs, across vast continents,

  • provided a solid theory for different researchers to use when designing studies in quantitative

  • and population genetics, and when trying to make sense of their results.

  • What did the Modern Synthesis look like as it happened? From 1928 to 1942, different

  • people applied one theory across a bunch of forms of empirical science, gluing them together.

  • Hence, “synthesis!”

  • They also published influential books that knit together Darwinism with Mendelismsuch

  • as English ecological geneticist E. B. Ford's 1931 classic, Mendelism and Evolution.

  • Now, there were too many Modern Synthesizers to shout out in one episode.

  • But you've met a couple of them before.

  • American geneticist and embryologist Thomas Hunt Morgan, for example, directed the Fly

  • Room at Columbia from 1911 to 1928—which we visited in Episode Twenty-Five.

  • Morgan trained a lot of biologists who contributed to the Modern Synthesis by exploring where

  • genes are physically located on the chromosomes of fruit flies

  • members of the species Drosophila melanogaster.

  • They Fly Boys also created databases of different alleles, or versions of a gene.

  • For example, they figured out that the dominant allele controlling the color of a fly's

  • eyes makes it red, but recessive alleles exist for brown or white eyes.

  • In fact, the Fly Room scientists could inbreed flies with specific traits until these mutants

  • were pretty much new species.

  • But this didn't prove how species were created in the wild.

  • Maybe, using artificial selection, the scientists were doing something that Darwin and Wallace's

  • proposed mechanism, natural selection didn't do, or did a different way.

  • One of Morgan's students, Ukrainian-American geneticist Theodosius Dobzhansky, resolved

  • this frustration by studying flies similar to the lab's Drosophila.

  • Traveling from Canada to Mexico, Dobzhansky demonstrated that natural groups of flies

  • have the same levels of genetic variation as mutants in labs.

  • In fact, Dobzhansky showed that, in the wild, variations are inherited pretty much as Darwin

  • would have predicted.

  • And most mutations aren't good or bad, which is why variation is so high! He joined the

  • worlds laboratory genetics, the realm of experimentation, and field naturalism, the realm of observation.

  • Dobzhansky published his landmark book, Genetics and the Origin of Species in 1937, which established

  • evolutionary genetics as a discipline.

  • In his book, Dobzhansky defined evolution as thechange in the frequency of an allele

  • within a gene pool.” Which is pretty much how we teach it today.

  • Darwin's natural selection, culling certain alleles from a population and allowing others

  • to reproduce, is one of the main drivers of the evolution of speciesalong with completely

  • random mutation and some other forces called gene flow and gene drift.

  • Dobzhansky also spent much of his career trying to convince people not to think of humans

  • like inbred mutant flies: humanracesare not genetically defined, but socially

  • constructed.

  • The biological features that people have associated with different races have changed over time,

  • and the boundaries between those races have been redrawn.

  • Dobzhansky was one of many scientists who hoped that people would read about human genetics

  • and suddenly change their views on human difference.

  • Turns out, we need more than just science.

  • Dobzhansky was not the only biologist to turn to statistics as a tool for describing variation

  • in living things.

  • Starting around 1918, English statistician Ronald A. Fisher made numerous contributions

  • to statistics and genetics, culminating in his banger, The Genetical Theory of Natural

  • Selection, in 1930.

  • He showed statistically that what looks like continuous natural selection is actually the

  • result of combined changes to many different genes.

  • Fisher's work provided much of the foundation for biostatistics, or how to apply statistics

  • to biology, including using statistical concepts to understand the results of experiments.

  • Unfortunately, Fisher was also a massive eugenicist who insisted that racial differences in humans

  • mattered scientifically.

  • Sort of the opposite of Dobzhansky.

  • English scientist, socialist organizer, and consummate natty dresser J. B. S. Haldane

  • also helped pioneer biostatistics, and a bunch of other stuff.

  • In a 1915 paper, Haldane published the first genetic linkage maps for mammalsshowing

  • the order and relative distances of genes in guinea pigs and mice, and later chickens.

  • This was a big step, moving from flies to mice!

  • Haldane's work, like his 1932 book The Causes of Evolution, helped establishwith Fisher

  • and American geneticist Sewall Wrightpopulation genetics.

  • This is the study of how genes vary in populations, including models of how different alleles

  • will change in a population over time.

  • Other scientists focused not on gene-by-gene change, but on whole species. German ornithologist

  • Ernst Mayr came up with the modern biological definition of a species:

  • not just a bunch of similar organisms, but a group that can only breed with each other.

  • Mayr published Systematics and the Origin of Species from the Viewpoint of a Zoologist

  • in 1942, helping establish evolutionary biology as distinct from genetics and the other life

  • sciences.

  • Finally, British evolutionary biologist and eugenicist Julian Huxley published Evolution:

  • The Modern Synthesis in 1942.

  • This one was kind of the capstone to the whole Modern Synthesis: it summarized the research

  • uniting evolution and genetics up to World War Two.

  • And Julian Huxley coined many terms still used by evolutionary biologists, such as cline,

  • or the gradient of some traitsay, some genewithin a population across a geographical

  • range.

  • Fun fact: Julian's little brother, Aldous Huxley wrote the dystopia Brave New World

  • in 1932, which argued that technology might not only not be the solution to the world's

  • problemsit might be a major source of them.

  • And we have to shout-out their grandpa, Thomas Henry Huxley, AKADarwin's Bulldog,”

  • who helped make Darwin the most famous scientist of the nineteenth century.

  • Just… a lot going on with the Huxley family.

  • So the Modern Synthesizers had links back to Darwin himself.

  • And with Julian Huxley's book, the work of figuring out the how of evolution was publicly

  • announced, a little less than a century after the Origin of Species.

  • In the public eye, biology gained credibility. After striving for decades to make their field

  • better resemble physics, biologists were finally using mathematics and massive data sets regularly

  • and convincingly.

  • It's important to note that the Synthesizers weren't really a clearly defined group,

  • and they didn't always agree with each other.

  • And while their work was transformative and still provides a basis for some of the day-to-day

  • work for biologists, not everyone was down with the Synthesis in the Forties, and new

  • ideas continue to reshape it today.

  • But still, by 1942, biology had become, by its own account, “modern.”

  • Notice, the Synthesizers were mostly English and American dudes. Dobzhansky was born in

  • the Ukraine, but he immigrated to the United States at age twenty seven.

  • While they were meticulously using Mendelian genetics to explain natural selection, their

  • counterparts in the newly powerful Soviet Union faced a different intellectual landscape.

  • Science and technology were strongly prized in the Soviet Union.

  • After all, the country had been founded on Marxist principles: there is only one, material

  • world, and whoever controls the means of productioncapital and technologycontrols that world.

  • After the World War Two, elite schools pumped out many highly skilled engineers every year,

  • and Soviet scientists began to win Nobel Prizes.

  • They had to catch up on the whole atomic bomb fad, for one.

  • But in the life sciences, instead of competing with the Modern Synthesizers, the Soviets

  • focused on applicationsagriculture.

  • The question facing Soviet geneticists was, how to improve varieties of wheat and other

  • staples so that they could grow longer, even in the harsh environments that made up a lot

  • of the Soviet Union?

  • ThoughtBubble, show us what happened next: Soviet agronomist Trofim Lysenko rose from

  • obscurity to become the director of the Soviet Union's Lenin All Union Academy of Agricultural Sciences.

  • all because he claimed that wheat subjected to cold would produce a next generation better

  • able to withstand even more cold.

  • This process was call vernalization, and it caught on, along with Lysenko's other ideas

  • for farming, faster than scientists could investigate whether they actually worked.

  • So now, promoted up to science boss, Lysenko focused on developing ideas similar to those

  • of Jean-Baptiste Lamarck,

  • the French evolutionary theorist who thought that organisms could inherit characteristics

  • based on their individual experiences.

  • This theory, in which experience mattered more than a competition among inherited genes,

  • was a better fit with Marxism.

  • Lysenko and his yes-men also made lots of unscientific claims about agriculture, including

  • that rye could transform into wheat.

  • He also used his power to destroy the careers of geneticists in the Soviet Unionall of

  • them.

  • He had the real scientists fired and replaced with his lackeys.

  • This system of science-purely-for-politics'-sake became known as Lysenkoism.

  • Now, all systems of science are politicalsaying you'reapoliticaljust means you're

  • for the status quobut Lysenkoism wasn't even science any more.

  • It was a pure power play.

  • So in 1940, the leading Soviet geneticist, Nikolai Vavilov , was arrested.

  • Lysenko took up his post as director of the Institute of Genetics.

  • In 1941, Vavilov was put through a sham trial and found guilty of sabotage. Imprisoned,

  • he died of malnutrition in 1943.

  • Thanks Thoughtbubble.

  • And then, in 1948, Lysenko talked Joseph Stalin into banning population genetics and other

  • types ofbourgeoisbiology entirely.

  • This meant no more artificial selection of crop varietals based on neo-Darwinian science.

  • The Soviet Union, already facing serious food shortages, lost an important tool for fighting

  • famine.

  • Lysenkoism only ended in the 1960s, after Lysenko's Stalin died, and three prominent

  • Soviet physicists spoke out against his pseudoscience and political manipulations.

  • But at least, thanks to scientists including Julian Huxley, Nikolai Vavilov's reputation

  • as a great geneticist was finally restored.

  • Next timeanother bridge from World War Two to the Cold War: it's time to meet Alan

  • Turing and invent the computer.

  • 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 Nature League, Sexplanations,

  • and Scishow.

  • 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 Crash Course possible with their continued

  • support.

By the end of World War Two and the beginning of the Cold War, physics had been revolutionizedagain.

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遺傳學與現代綜合》。科學史速成班#35 (Genetics and The Modern Synthesis: Crash Course History of Science #35)

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    林宜悉 發佈於 2021 年 01 月 14 日
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