Genetics and The Modern Synthesis: Crash Course History of Science #35


By the end of World War Two and the beginning
of the Cold War, physics had been revolutionized—again. 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 biology—one 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, or “neo-Darwinism.” And even today, biologists mostly work within it. Basically, the Modern Synthesis uses Mendelian
inheritance—Mendel’s rules—to 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 Mendelism—such 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 the “change 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 species—along 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: human “races”
are 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 mammals—showing 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 establish—with Fisher and American geneticist Sewall Wright—population
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 trait—say, some
gene—within 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 problems—it might be a major source of them. And we have to shout-out their grandpa, Thomas
Henry Huxley, AKA “Darwin’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 production—capital
and technology—controls 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 applications— agriculture. 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 Union—all 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 political—saying
you’re “apolitical” just means you’re for the status quo—but 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 of “bourgeois” biology 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 time—another 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
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