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.
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