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| Duration: | 12:26 |
| Uploaded: | 2026-03-17 |
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| MLA Full: | "What Happens When Science Clashes with the Public?: Crash Course Scientific Thinking #7." YouTube, uploaded by CrashCourse, 17 March 2026, www.youtube.com/watch?v=NaMcw8_10Yg. |
| MLA Inline: | (CrashCourse, 2026) |
| APA Full: | CrashCourse. (2026, March 17). What Happens When Science Clashes with the Public?: Crash Course Scientific Thinking #7 [Video]. YouTube. https://youtube.com/watch?v=NaMcw8_10Yg |
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CrashCourse, "What Happens When Science Clashes with the Public?: Crash Course Scientific Thinking #7.", March 17, 2026, YouTube, 12:26, https://youtube.com/watch?v=NaMcw8_10Yg. |
We know smoking causes cancer. But the journey to that knowledge is way wilder than you think. In our last episode of Crash Course Scientific Thinking, we’ll explore what happens when scientific research clashes with public opinion, individual values, and corporate interests.
Introduction: Smoking Causes Cancer 00:00
Empirical Evidence 0:39
Researching Lung Cancer 1:54
Manufactured Doubt 4:15
The Fall of Tobacco 7:03
Individual Choice & Values 7:36
Takeaways from the War on Smoking 8:31
Review & Credits 10:43
Sources: https://docs.google.com/document/d/1Kv2_mFsDxQURuFDxpflD45dy-pCxlqnM9iPSNYxigmQ/edit?tab=t.0#heading=h.vk5i2fgqyumq
***
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Mike Cumings, Jr., NassauLinda, Chuck Smith, DexcilaDou, Martin G. Diller, Johnathan Williams, Allison Wood, Katrix , Jason Terpstra, Evan Nelson, Jennifer Wiggins-Lyndall, SpaceRangerWes, Dalton Williams, Chelsea S, Matthew Fredericksen, Michael Maher, AThirstyPhilosopher ., Mitch Gresko, Gina Mancuso, Roger Harms, Shruti S, Quinn Harden, Reed Spilmann, Stephen Akuffo, Andrew Woods, Kevin Knupp, UwU, David Fanska, oranjeez, Brandon Thomas, Toni Miles, Elizabeth LaBelle, Emily Beazley, Leah H., Rie Ohta, Barbara Pettersen, Ken Davidian, Tanner Hedrick, Trevin Beattie, Eric Koslow, Les Aker, Samantha, Laurel Stevens, Pietro Gagliardi, Alan Bridgeman, Stephen McCandless, Alex Hackman, Steve Segreto, Liz Wdow, Constance Urist, Thomas, Katie Dean, ClareG, Indija-ka Siriwardena, Jennifer Killen, Kristina D Knight, Nathan Taylor, John Lee, Evol Hong, Kyle & Katherine Callahan, Emily T, Breanna Bosso, Bernardo Garza, Rizwan Kassim, Jason Buster, Wai Jack Sin, Scott Harrison, Triad Terrace, Ian Dundore, Sarah & Nathan Catchings, Ken Penttinen, Barrett, Krystle Young, Duncan W Moore IV, Matt Curls, Erminio Di Lodovico, Perry Joyce, Siobhán, team dorsey, Joseph Ruf, Jason Rostoker, Luke Sluder, Caleb Weeks, Tandy Ratliff
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Introduction: Smoking Causes Cancer 00:00
Empirical Evidence 0:39
Researching Lung Cancer 1:54
Manufactured Doubt 4:15
The Fall of Tobacco 7:03
Individual Choice & Values 7:36
Takeaways from the War on Smoking 8:31
Review & Credits 10:43
Sources: https://docs.google.com/document/d/1Kv2_mFsDxQURuFDxpflD45dy-pCxlqnM9iPSNYxigmQ/edit?tab=t.0#heading=h.vk5i2fgqyumq
***
Support us for $5/month on Patreon to keep Crash Course free for everyone forever! https://www.patreon.com/crashcourse
Or support us directly: https://complexly.com/support
Join our Crash Course email list to get the latest news and highlights: https://mailchi.mp/crashcourse/email
Get our special Crash Course Educators newsletter: http://eepurl.com/iBgMhY
Thanks to the following patrons for their generous monthly contributions that help keep Crash Course free for everyone forever:
Mike Cumings, Jr., NassauLinda, Chuck Smith, DexcilaDou, Martin G. Diller, Johnathan Williams, Allison Wood, Katrix , Jason Terpstra, Evan Nelson, Jennifer Wiggins-Lyndall, SpaceRangerWes, Dalton Williams, Chelsea S, Matthew Fredericksen, Michael Maher, AThirstyPhilosopher ., Mitch Gresko, Gina Mancuso, Roger Harms, Shruti S, Quinn Harden, Reed Spilmann, Stephen Akuffo, Andrew Woods, Kevin Knupp, UwU, David Fanska, oranjeez, Brandon Thomas, Toni Miles, Elizabeth LaBelle, Emily Beazley, Leah H., Rie Ohta, Barbara Pettersen, Ken Davidian, Tanner Hedrick, Trevin Beattie, Eric Koslow, Les Aker, Samantha, Laurel Stevens, Pietro Gagliardi, Alan Bridgeman, Stephen McCandless, Alex Hackman, Steve Segreto, Liz Wdow, Constance Urist, Thomas, Katie Dean, ClareG, Indija-ka Siriwardena, Jennifer Killen, Kristina D Knight, Nathan Taylor, John Lee, Evol Hong, Kyle & Katherine Callahan, Emily T, Breanna Bosso, Bernardo Garza, Rizwan Kassim, Jason Buster, Wai Jack Sin, Scott Harrison, Triad Terrace, Ian Dundore, Sarah & Nathan Catchings, Ken Penttinen, Barrett, Krystle Young, Duncan W Moore IV, Matt Curls, Erminio Di Lodovico, Perry Joyce, Siobhán, team dorsey, Joseph Ruf, Jason Rostoker, Luke Sluder, Caleb Weeks, Tandy Ratliff
__
Want to find Crash Course elsewhere on the internet?
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Facebook - http://www.facebook.com/YouTubeCrashCourse
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CC Kids: http://www.youtube.com/crashcoursekids
(00:00) to (02:00)
Hank Green: Smoking causes cancer.
I know that, you know that, and the tobacco industry definitely knows that.
But not all that long ago, you couldn't even watch Saturday morning cartoons without being bombarded with messages that cigarettes aren't that bad for you.
Tobacco companies ran ads in magazines and periodicals saying that numerous scientists question smoking's risks, that there are many possible causes of lung cancer,and that there's no proof cigarette smoking is one of them.
So, if you had been there, how would you have figured out what was true?
Hi, I'm Hank Green, and this is Crash Course Scientific Thinking
[Theme music]
Before scientific knowledge reaches people like you and me, it takes a long arduous journey, and big stretches of it are dedicated to collecting, testing, and scrutinising empirical evidence, information collected through rigorous scientific methods that either support or refute an idea.
The vast majority of scientific progress hums along quietly, its evidence becoming widely accepted without much hullabaloo.
You won't hear pundits debate whether carbon has 6 protons, and there won't be dramatic headlines about the mating behaviour of sea slugs.
Though I, for one, definitely would and do read those articles.
But here's the thing, sometimes science produces a nugget of knowledge that resists the status quo. It challenges an economic system, or a hierarchy, or a choice people make in their lives. And when it lands with the public, tensions can flare.
Which is what happened in 1964 with smoking.
So, in this episode, we're going to do two things. First, we'll peel back the curtain on how the scientific process pieced together evidence about the risks of smoking, and then we'll unpack why that knowledge got so much pushback, and what we can learn from the tale about the public consumption of science news. [Drinks test tube contents]
At the beginning of the 20th century, lung cancer was so rare doctors treated cases of it like once-in-a-lifetime learning opportunities.
(02:00) to (04:00)
But then in the 1920s and 30s, lung cancer rates started to spike, and scientists began working to figure out why.
There were a lot of early ideas about the possible cause. Maybe it eas atmospheric pollution or newly paced roads. Maybe it was x-rays, poison gas from World War I, or the after-effects of the 1918 flu pandemic.
Those were all correlations, but as we learned in an earlier episode, correlation doesn't mean causation.
So over two decades, scientists tested different explanations and shared the results with each other. Each study was a pebble added to a pile of evidence.
Scientists had to weigh that evidence by examining each study sceptically and asking things like, "How well was the study designed?" "Did it find a strong or weak relationship to lung cancer?" and "How directly did the methods actually get at the question they were trying to answer?"
For some explanations, no evidence emerged. You're off the hook, flu.
But eventually, 4 main lines of evidence pointed to one suspect.
Exhibit A, observational studies, which had followed groups of people over a period of time showed that smokers developed lung cancer at higher rates than non-smokers.
But there were other factors in people's lives that could be affecting cancer rates, so these studies alone weren't enough.
Enter Exhibit B, experimental studies were done on mice, because you can better control conditions in a lab, and mice exposed to tobacco developed tumours
But how? What actually happens when lungs are exposed to smoke?
Exhibit C, further studies showed that cigarette smoke destroys cilia, the tiny structure in lungs that keep out bad stuff.
And finally, exhibit D, tobacco smoke itself contains a chemical compound that was previously shown to cause cancer in people exposed to tar.
All that evidence, when weighed collectively, began to tip the scales. By the late 1950s, scientists had reached a consensus, widespread agreement given all the evidence that smoking was the leading cause of lung cancer.
Scientists had to weigh that evidence by examining each study sceptically and asking things like, "How well was the study designed?" "Did it find a strong or weak relationship to lung cancer?" and "How directly did the methods actually get at the question they were trying to answer?"
For some explanations, no evidence emerged. You're off the hook, flu.
But eventually, 4 main lines of evidence pointed to one suspect.
Exhibit A, observational studies, which had followed groups of people over a period of time showed that smokers developed lung cancer at higher rates than non-smokers.
But there were other factors in people's lives that could be affecting cancer rates, so these studies alone weren't enough.
Enter Exhibit B, experimental studies were done on mice, because you can better control conditions in a lab, and mice exposed to tobacco developed tumours
But how? What actually happens when lungs are exposed to smoke?
Exhibit C, further studies showed that cigarette smoke destroys cilia, the tiny structure in lungs that keep out bad stuff.
And finally, exhibit D, tobacco smoke itself contains a chemical compound that was previously shown to cause cancer in people exposed to tar.
All that evidence, when weighed collectively, began to tip the scales. By the late 1950s, scientists had reached a consensus, widespread agreement given all the evidence that smoking was the leading cause of lung cancer.
(04:00) to (06:00)
So, in 2964, the US Surgeon General, himself a smoker, announced to reporters that cigarettes cause ling cancer.
But for the public, that message got drowned out by a lot noise. So, let's rewind the tape, and this time, let's look at what was going on in the public view.
Even in the 1930s, people suspected smoking wasn't exactly great for you, but tobacco companies worked to stay ahead of the narrative, boasting that their cigarettes were healthier, safer, gentler, fresh as mountain air. [Hank coughing smoke]
The RJ Reynolds Tobacco Company ran ads citing studies that claimed more doctors smoke Camels than any other cigarette.
And you want to know how they got that statistic? By giving doctors free Camel cigarettes and then asking then asking them what kind of cigarettes they smoked. I mean, come on.
By the 1950s, tobacco companies knew about the mounting scientific evidence, but they were still invested in selling their product, so they changed the message.
Instead of our cigarettes are better for you, the ads became we don't know yet if cigarettes are bad for you. And by doing so, they manufactured a controversy that didn't actually exist.
This is where things get wild. In 1954, a committee called the Tobacco Industry Research Committee, which was formed by the tobacco companies, released a statement claiming the link between smoking and lung cancer wasn't settled, and they would be researching the issue themselves.
These people would have thrived on social media.
This went on for decades, long after the scientific consensus had been settled.
The tobacco industry distracted from smoking's harms by funding and publicising research looking into alternative explanations for lung cancer.
They suppressed and criticised studies that found smoking was bad for you, and all the while, they publicly denied that smoking was risky or addictive, and blasted ads that made cigarettes seem as enticing as possible.
(06:00) to (08:00)
They did all of this knowingly and strategically to keep making money.
A 1969 internal memo at the tobacco company Brown & Williamson stated, "Doubt is our product, since it is the best means of competing with the 'body of fact' that exists in the mind of the general public. It is also the means of establishing a controversy."
Wow, they just said it.
And selling that doubt worked. The tobacco industry preyed upon people's cognitive biases, those predictable patterns our brains tend to take that can sway us away from accepting valid information, especially when it challenges something we already do or think.
The news that smoking causes cancer just didn't vibe with a world where smoking was common, widely accepted, and everybody did it. Doctors, astronauts, movie stars.
Plus, cigarettes are highly addictive. When you're addicted to something, you pay more attention to reasons to keep doing that thing, and the tobacco industry was willing to give smokers those reasons, even though the reasons were made up.
They systematically attacked the widely accepted scientific explanation in order to sow doubt among the public.
But here’s what finally turned the tide against smoking. In the 1990s, scientists uncovered evidence of exactly how cigarette smoke can trigger a normal cell to become a cancerous cell.
Then in 1998, a major settlement required the tobacco industry to pay up billions of dollars for the damage they had caused.
The writing was on the wall, but the tobacco industry still tried to spin the narrative. The message this time, they claimed they'd always been transparent about the risks of smoking, and said that it had always been an individual's choice to take those risks.
Which brings me to another common point of tension that can make scientific knowledge seem controversial.
Sometimes, scientific knowledge clashes with people's values. There's stuff science can tell us, like the precise mechanism that causes a cell to become cancerous, or how much smoking increases your individual risk of developing cancer.
But, science can't tell us what to do with that knowledge.
(08:00) to (10:00)
It's on us, as individuals and as societies, to decide what to do now that we know what we know.
For example, in the early 2000s, as the dangers of secondhand smoke became more widely known, many cities and states began banning smoking in public places.
Not everybody agreed with the move, but the disagreement wasn't over the science, it was about how that knowledge should mesh with the values.
What's more important, as person's freedom to make their own choices with their own body, or a person's freedom to protect their body from the choices someone else is making?
Science can't answer those questions, and I can't answer these questions for you.
So, you might be wondering, why did I even tell you all this?
You can think of the war over smoking as a kind of fable. It's a story that can teach us something, like the tortoise and the hare, or the boy who cried wolf, except it really happened.
And there are three lessons we can take away from this story that can help us navigate the wilderness where science and public opinion meet.
First, follow the scientific consensus. When a certain idea is backed by broad agreement among experts, it is already cleared an extraordinarily high bar of skepticism. I trust the experts for a reason.
Like, when I notice an electrical outlet is broken, I could try to fix it myself, but I will at best spend much more time and do a much shabbier job than an electrician would. At worst, I'll look like this. [Image of an electrocuted Hank]
The same is true with science. You'll have better information and get better outcomes when you trust the process of science.
So, when there is scientific consensus, pay attention to it.
Second, when there isn't yet consensus, we should be skeptical of science-related claims we encounter and keep in mind that a single study doesn't settle anything.
The studies we do hear about, the ones that make headlines, are the ones that have a surprising or attention-grabbing angle.
But a single study is just one pebble of evidence on the pile. You should look to what other experts say about it to understand how that study compares to the rest of the evidence, and how much it actually changes what we know.
Third, in science, challenging or debating an idea has a very different meaning than it often has in everyday life.
(10:00) to (12:00)
Even with a strong consensus, not every scientist agrees on every detail of an issue.
But scientists don't hold evidence back or try to keep other scientists from finding the flaws in their argument. They put it all on the table. They share everything they know, all of the evidence in good faith, so that their ideas can be challenged well.
That's the whole point.
Sage: See, kids, you like arguing. You can make a whole career of it
Hank: Sage, I don’t think you were scheduled for today.
Sage: I just had to say goodbye to the people, eh?
Hank: It's been a pleasure to have you along, Sage.
Sage: Oh, I'll be back.
Hsnk: Oh, is that a teaser?
Sage: Yeah, it might be. Bye, people! Hope you enjoyed your Sage advice.
Hank: Thanks, Sage.
There are times when scientific knowledge seems controversial to the public eye, but actually isn't controversial among the experts who know it best.
That's why the argument that smoking causes cancer wasn’t just an opinion among other opinions.
Often, when a scientific idea sparks controversy among the public, it's because it challenges our biases, our values, or powerful interests.
Scientific consensus is so impactful because it happens independent of those external considerations. And it's why science, the process, is so powerful at helping us become less wrong over time.
As we wrap up this series, I'll leave you with this.
When we recognise how science really works, the world makes so much more sense. We can be skeptical of individual studies, yet place trust in the collective process.
We can appreciate the long journey an idea takes before it becomes widely accepted knowledge, yet be open to ideas changing with new evidence. And we can know that if an idea is wrong, there's a good chance scientists will find out.
From all of us here at Crash Course, thanks for watching.
This episode of Crash Course Scientific Thinking was produced in partnership with HHMI BioInteractive, bringing real science stories to thousands of high school and undergrad life sciences classrooms.
(12:00) to (12:26)
If you're a teacher, visit their website for resources that explore the topics we discussed today in this video.
Thanks for watching this episode of Crash Course Scientific Thinking, which was filmed in Missoula, Montana, and was made with the help of all these nice people. If you want to keep Crash Course free for everyone forever, you can join our community on Patreon.