Hank takes us through the bowels of the human digestive system and explains why it's all about surface area.

In which John Green teaches you about disease, and the effects that disease has had in human history. Disease has been with man since the beginning, and it has shaped the way humans operate in a lot of ways. John will teach you about the Black Death, the Great Dying, and the modern medical revolution that has changed the world.

In which John Green teaches you a little bit about drought, which is a natural weather phenomenon, and famine, which is almost always the result of human activity. Throughout human history, when food shortages strike humanity, there was food around. There was just a failure to connect those people with the food that would keep them alive. There are a lot of reasons that food distribution breaks down, and John is going to teach you about them in the context of the late-19th century famines that struck British India.

Today we’re talking about mass transfer. It doesn’t just apply to objects and fluids as a whole, but also to the individual molecules and components that make them up. We’ll see that transfers of mass need their own driving force, discuss diffusion, and use Fick’s Law to help us model mass transfer.

We’re continuing our exploration of conflict theories with W.E.B. Dubois, who is one of the founders of sociological thought more broadly and the founder of race-conflict theory. We’ll discuss shifting ideas about race, Dubois’ idea of ‘double-consciousness’, and the modern day field of racial identity. We’ll explore the idea racial formation and discuss Dubois’ survey of African Americans in Philadelphia to look at how economic, political, and social structures affect how we perceive different races – and vice versa. We’ll also discuss the activist side of Dubois’ life as co-founder of the NAACP and editor of the Crisis, and how modern day sociologists study racial politics and racial resistance.

It's Earth Science time!!!! In this field, natural philosophers were asking questions like, what’s up with fossils? Are they the remains of extinct organisms? Or are they so-called “sports of nature”—rocks that just happen to look like living things but don’t /mean/ anything? And most importantly, how old is… everything?

In the world of ecology, the only constant is change - but change can be good. Today Hank explains ecological succession and how ecological communities change over time to become beautiful, biodiverse mosaics.

Hank introduces us to ecology - the study of the rules of engagement for all of us earthlings - which seeks to explain why the world looks and acts the way it does. The world is crammed with things, both animate and not, that have been interacting with each other all the time, every day, since life on this planet began, and these interactions depend mostly on just two things... Learn what they are as Crash Course Biology takes its final voyage outside the body and into the entire world.

This week we’ll see how economies can be broken down into the primary, secondary, and tertiary sectors. We’ll look at the three stages of economic revolution that brought us to the modern post-industrial era. We’ll also explore two types of economic models: capitalism and socialism.

Hank brings us to the next level of ecological study with ecosystem ecology, which looks at how energy, nutrients, and materials are getting shuffled around within an ecosystem (a collection of living and nonliving things interacting in a specific place), and which basically comes down to who is eating who.

Today we’ll explore the history of education as a social institution, with a specific focus on how the US organizes its educational system. We’ll look at education through the lenses of some sociological paradigms: structural functionalist approaches (including some of the manifest and latent functions associated with education), and a symbolic interactionist approach to education that shows us how self-fulfilling prophecies in educational settings contribute to differences in academic outcomes for students.

Today we’re going to go a little meta and talk about how computer science can support learning with educational technology. We here at Crash Course are big fans of interactive in-class learning and hands-on experiences, but we also believe in the additive power of educational technology inside and outside the classroom from the Internet itself and Massive Open Online Courses, or MOOCs to AI driven intelligent tutoring systems and virtual reality.

There was physics before Einstein in the same way that there was biology before Darwin. Einstein didn’t just add some new ideas to physics. And he didn’t just add a unifying framework for doing physics, like Newton. Einstein took what people thought was physics, turned it upside down, then turned it inside out.

Today, we'll explore the materials electrical engineers work with. We'll look at high-conductors, insulators, and how low-conductivity conductors can be used to generate light and heat.

The study of electricity goes all the way back to antiquity. But, by the time electricity started to become more well known, a few familiar names started to appear. Edison, Galvani, and a few others really changed the way the world worked.

So we ended last episode at the start of the 20th century with special purpose computing devices such as Herman Hollerith’s tabulating machines. But as the scale of human civilization continued to grow as did the demand for more sophisticated and powerful devices. Soon these cabinet-sized electro-mechanical computers would grow into room-sized behemoths that were prone to errors. But is was these computers that would help usher in a new era of computation - electronic computing.

In which John Green teaches you about the Bronze Age civilization in what we today call the middle east, and how the vast, interconnected civilization that encompassed Egypt, The Levant, and Mesopotamia came to an end. What's that you say? There was no such civilization? Your word against ours. John will argue that through a complex network of trade and alliances, there was a loosely confederated and relatively continuous civilization in the region. Why it all fell apart was a mystery. Was it the invasion of the Sea People? An earthquake storm? Or just a general collapse, to which complex systems are prone? We'll look into a few of these possibilities. As usual with Crash Course, we may not come up with a definitive answer, but it sure is a lot of fun to think about.

This week we are looking at renewable energy sources and why we need them. We’ll explore hydropower, wind, geothermal, and solar power, as well as some of the challenges, and how engineers are working to make their use more widespread.

We’ve talked about many important concepts for engineers, but today we’re going to discuss a hugely important one that you might not even realize is an engineering concept: ethics. We’ll talk about what a Code of Ethics is. We’ll explore engineering ethics and the ethical theories of utilitarianism, rights ethics, and duty ethics. We’ll also take a look at a few different real life examples of ethical problems in engineering.

This week, we're headed back to England to learn about Sentimental Comedies. They weren't that funny, but they were definitely sentimental. The people of England were shaking off the Restoration hangover, and bawdy plays no longer had a place. In fact, there wasn't a place for much of any drama, as only two theaters were licensed to present plays. Rules and regulations everywhere, y'all.