Interactions between species are what define ecological communities, and community ecology studies these interactions anywhere they take place. Although interspecies interactions are mostly competitive, competition is pretty dangerous, so a lot of interactions are actually about side-stepping direct competition and instead finding ways to divvy up resources to let species get along. Feel the love?

Hank gets to the more violent part of community ecology by describing predation and the many ways prey organisms have developed to avoid it.

Hank introduces us to comparative anatomy, which studies the similarities and differences in animal anatomy to support the theory of evolution and the shared ancestry of living things.

Hank continues our exploration of animal phyla with the more complexly organized annelida and arthropoda, and a biolography on insects.

So last episode we talked about some basic file formats, but what we didn’t talk about is compression. Often files are way too large to be easily stored on hard drives or transferred over the Internet - the solution, unsurprisingly, is to make them smaller. Today, we’re going to talk about lossless compression, which will give you the exact same thing when reassembled, as well as lossy compression, which uses the limitations of human perception to remove less important data. From listening to music and sharing photos, to talking on the phone and even streaming this video right now the ways we use the Internet and our computing devices just wouldn’t be possible without the help of compression.

Today we start a three episode arc on the rise of a global telecommunications network that changed the world forever. We’re going to begin with computer networks, and how they grew from small groups of connected computers on LAN networks to eventually larger worldwide networks like the ARPANET and even the Internet we know today. We'll also discuss how many technologies like Ethernet, MAC addresses, IP Addresses, packet switching, network switches, and TCP/IP were implemented to new problems as our computers became ever-increasingly connected. Next week we’ll talk about the Internet, and the week after the World Wide Web!

Today we’re going to talk about how computers see. We’ve long known that our digital cameras and smartphones can take incredibly detailed images, but taking pictures is not quite the same thing. For the past half-century, computer scientists have been working to help our computing devices understand the imagery they capture, leading to advancements everywhere, from tracking hands and whole bodies, biometrics to unlock our phones, and eventually giving autonomous cars the ability to understand their surroundings.

Today we’re going to talk about confidence intervals. Confidence intervals allow us to quantify our uncertainty, by allowing us to define a range of values for our predictions and assigning a likelihood that something falls within that range. And confidence intervals come up a lot like when you get delivery windows for packages, during elections when pollsters cite margin of errors, and we use them instinctively in everyday decisions. But confidence intervals also demonstrate the tradeoff of accuracy for precision - the greater our confidence, usually the less useful our range.

In which John Green teaches you about conflict in Israel and Palestine. This conflict is often cast as a long-term beef going back thousands of years, and rooted in a clash between religions. Well, that's not quite true. What is true is that the conflict is immensely complicated, and just about everyone in the world has an opinion about it. John is going to try to get the facts across in under 13 minutes.

Hank wraps up the Crash Course on ecology by taking a look at the growing fields of conservation biology and restoration ecology, which use all the kung fu moves we've learned about in the past eleven weeks and apply them to protecting ecosystems and to cleaning up the messes that we've already made.

We may be living IN a simulation (according to Elon Musk and many others), but that doesn't mean we don't need to perform simulations ourselves. Today, we're going to talk about good experimental design and how we can create controlled experiments to minimize bias when collecting data. We'll also talk about single and double blind studies, randomized block design, and how placebos work.

This week, Stan Muller teaches you the basics of copyright in the United States. Copyright law is territorial, so we're going to cover the system we know the most about, and that's the US. Stan will talk about what kind of ideas can be copyrighted, who can get a copyright, and what protections the copyright grants. We'll also talk about the always contentious and seemingly ever-growing term of copyright. Stan will also teach you about the low bar for creativity, which means that original work doesn't have to be all that original, and he'll also touch on the problems with copyright in the modern world.

Stan Muller teaches you a few things about copyright enforcement, and talks about the exceptions to copyright enforcement. While there are several, the one you've probably heard of is Fair Use, and it's a pretty tricky one. We'll try to explain it, and teach you just why fair use is so loosey goosey.

Today we’re going to talk about data relationships and what we can learn from them. We’ll focus on correlation, which is a measure of how two variables move together, and we’ll also introduce some useful statistical terms you’ve probably heard of like regression coefficient, correlation coefficient (r), and r^2. But first, we’ll need to introduce a useful way to represent bivariate continuous data - the scatter plot. The scatter plot has been called “the most useful invention in the history of statistical graphics” but that doesn’t necessarily mean it can tell us everything. Just because two data sets move together doesn’t necessarily mean one CAUSES the other. This gives us one of the most important tenets of statistics: correlation does not imply causation.

Starting February 22nd, Carrie Anne Philbin will be hosting Crash Course Computer Science! In this series, we're going to trace the origins of our modern computers, take a closer look at the ideas that gave us our current hardware and software, discuss how and why our smart devices just keep getting smarter, and even look towards the future! Computers fill a crucial role in the function of our society, and it's our hope that over the course of this series you will gain a better understanding of how far computers have taken us and how far they may carry us into the future.

In our first episode of Crash Course Engineering, Shini explains what engineering is, and gives a brief overview of its four main branches (civil, mechanical, electrical, and chemical) as well as a look at some of the other fields of engineering.

CrashCourse offers many YouTube videos that support various historical topics, such as sociology, world history, and much more!

For as long as Hank has hosted Crash Course, he's wanted to host a series about the history of science. We've been asking big questions for a really long time and we've all wanted to explore how we've sought to answer those questions through the centuries. Questions like, "What is stuff?" and "Where are we?" have inspired people all over the world to investigate. So lets dive in and see how we, as a people, have tried to figure this stuff out.

Crash Course Kids combines the same engaging lecture-style content delivery with animated graphics that focus on grade school science.

Topics include Earth Science, Physical Science, Biology, Geography, Engineering, and Astronomy.

These videos are amazing!

Join Jay Smooth next week for the start of our next miniseries: Crash Course Media Literacy!