Robert Sapolsky, a Stanford biologist, is currently one of the most publicly accessible science writers in the country, perhaps best known for his book on stress, Why Zebras Don't Get Ulcers. In the lecture above, Sapolsky takes a hard look at depression. The topic is a little heavy. I'll grant that. But, it's also important. As Sapolsky is quick to point out, depression is pervasive and getting worse. Currently, it's the 4th greatest cause of disability worldwide, and it will soon become the 2nd. For Sapolsky, depression is deeply biological; it is rooted in biology, just like, say, diabetes. Here, you will see how depression changes the body. When depressed, our brains function differently while sleeping, our stress response goes way up 24/7, our biochemistry levels change, etc. Given the pervasiveness of depression, this video is well worth a watch.