As we put Thanksgiving well behind us, let's linger just a moment on a question about transcontinental migration: When Eurasians traveled west, why didn't they pick up plagues from the New World? Much of the New World was ravaged by Old World plagues, but the reverse just didn't happen—at least, not remotely to the level we might expect when two groups of people make first contact.

In 1997, Jared Diamond set out to address this question in his book Guns, Germs, and Steel: The Fates of Human Societies. (He also tackled various other questions, and in 1998 won a Pulitzer Prize for the book. It's well worth a read!) In the video below, YouTube explainmaestro CGP Grey takes on the topic inspired by Diamond, asking, in short, why was there no Americapox? Have a look:

For a transcript and further reading, check out Grey's website.