When wolves were reintroduced to Yellowstone National Park in the United States after being absent nearly 70 years, the most remarkable "trophic cascade" occurred. What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains the process.

Seattle artist Matt Sellars shows off the Clovis Point, a skateboard of his own design. Check out a few scenes from its construction and test drive!

David and Ben Crystal explain why Shakespeare verses read with Original Pronunciation convey very different emotions and open up another level of understanding.

Several boats converge near the largest of the Farallon Islands when killer whales are spotted. But what they think is a young killer whale turns out to be a great white shark.

The great white shark and killer whale are both infamous marine predators. Normally they leave each other alone, but one day, biologists off the cost of California witness something unprecedented.

Rozalia Project knows all about marine debris. Do you? Take a look at their wrap-up video from Expedition CLEAN on the Gulf of Maine in August of 2014.

Within a deep and narrow cave in South Africa, paleoanthropologist Lee Berger and his team found fossil remains belonging to the newest member of our human family. The Homo naledi discovery adds another exciting chapter to the human evolution story by introducing an ancestor that was primitive, but shared physical characteristics with modern humans.

In this final installment of the series, a white Kermode bear encounters a black bear while fishing. Observe their behavior. Look and see for yourself what ensues!

The salmon that make it upstream mate and then die of exhaustion. Meanwhile, many other animals are lurking and waiting to feed.

In this episode, we see how the bears coexist with other creatures in their environment, and also learn about the role of the bear in Tsimshian lore. Enjoy!

In order to fatten up before winter sets in, brown bears feast upon salmon migrating upstream to spawn. Enjoy!.

Catch glimpses of sockeye salmon, also called red salmon, as they make their way upstream in a migration known as the "red flood." Also included is footage of dippers, which are some of the only songbirds that search for food on the bottom of a body of water.

In summer, mother bears and their young cubs can be spotted on the plains near Hallo Bay in Alaska's Katmai National Park.

Observe more stunning footage from Alaska of the bald eagle and the black bear. And finally catch a first glimpse of the rare glacier bear. Enjoy!

More stunning footage from Alaska shows, up close and personal, the brown bears in action - hunting for salmon and caring for their young. Enjoy!