There’s an immense world of tiny stuff within us and around us—but how do we know about it? In this episode of Crash Course Biology, we’ll discover how we see what we can’t see, thanks to the help of centuries-old tools and more recent...

This is a love letter to water, life’s solvent, and one of the most wonderful molecules around. In this episode of Crash Course Biology, we’ll learn about how water’s polarity and hydrogen bonding help it sustain life on a larger scale....

Despite the diverse appearance and characteristics of organisms on Earth, the chemicals that make up living things are remarkably similar, often identical. In this episode of Crash Course Biology, we’ll look at the building blocks of the...

Crocodiles, and birds, and dinosaurs—oh my! While classifying organisms is nothing new, phylogeny— or, grouping organisms by their evolutionary relationships—is helping us see life in a whole new light. In this episode of Crash Course...

Humans may have been around for a long time, but life has existed for way longer. In this episode of Crash Course Biology, we’ll journey through deep time to uncover the history of life on Earth. We’ll explore the big, game-changing...

How can you tell two species apart? It’s not always simple. In this episode of Crash Course Biology, we’ll learn about speciation—a process that can happen over millions of years, or within a single generation. Along the way, we’ll...

There are lots of ways that evolution happens, and natural selection is just one of them. In this episode of Crash Course Biology, we’ll find out how this process works and shapes traits in all living things —from ginkgo trees to howler...

Whether we’re talking about tigers, trees, or tarantulas, evolution happens at the level of the population. In this episode of Crash Course Biology, we’ll find out how natural selection, gene flow, genetic drift, and other processes...

Climate change shakes up all of Earth’s systems, including the living ones. In this episode of Crash Course Biology, we’ll see how climate change’s effects rattle the entire chain of life. Changes felt in one population ripple out to...

Life on Earth has weathered boiling-hot oceans and volcanic-ash-darkened skies—but that’s nothing like the climate change we’re experiencing now. In this episode of Crash Course Biology, we’ll talk about the greenhouse effect, learn why...

When the Bald Eagle population started to decline in the mid-20th century, scientists began to ask why. Population ecology, the study of organisms of the same species, played a big role in answering that question. In this episode of...

Community ecology is the study of interactions between different species of living things, and lets ecologists examine the effects of predator-prey relationships, parasites, and mutually beneficial interactions. In this episode of Crash...

Ecology is the study of the interactions of living things with each other and their environment. It’s a field that not only lets us explore the interconnections between living things, but also how our environment affects us, and how we...

Here on Earth, life is dizzyingly diverse—but it’s also surprisingly organized. A sense of order structures life and its processes, from the tiniest cell to the total sum of every living thing. In this episode of Crash Course Biology,...

We've been talking about the unavoidables recently. Last time, we covered Death. This time, it's taxes. So, what are taxes? Why do we pay taxes? What is all that tax money used for? This week, Adriene is going to cover all that and more....

Profit, revenue, income, assets, cash flow -- all these words mean money, but they all have specific uses. In business, money is important to us and we want to describe it as accurately as possible.

In which John Green teaches you about World War I and how it got started. Crash Course doesn't usually talk much about dates, but the way that things unfolded in July and August of 1914 are kind of important to understanding the Great...

So we have Weather and Climate... but are they the same thing? No, no they are not. But they are both super important to how the geosphere is shaped. In this episode of Crash Course Kids, Sabrina chats with us about the differences...

So, what's the difference between 'weather' and 'severe weather'? Is it just how hard the wind is blowing? Is it just thunder and lighting? Well, it can be some or all of those things. In this episode of Crash Course Kids, Sabrina talks...

Sex is complicated for different reasons in different cultures. But, it's the entire purpose of life, so there's no reason to blush. In this episode of Crash Course Psychology, Hank talks about Kinsey, Masters and Johnson, Sexuality,...

In which John Green teaches you WHY World War I started. Or tries to anyway. With this kind of thing, it's kind of hard to assign blame to any one of the nations involved. Did the fault lie with Austria-Hungary? Germany? Russia? Julius...

At the end of World War II, the nations of Europe were a shambles. Today we'll learn about how the various countries and blocs approached the problem of rebuilding their infrastructure and helping their residents recover. You'll learn...

How much should you get paid for your job? Well, that depends on a lot of factors. Your skill set, the demand for the skills you have, and what other people are getting paid around you all factor in. In a lot of ways, labor markets work...

There are several ways the world could end, and scientists have given a lot of thought to what the last living thing will be.