Romantic chemistry is all about warm, gooey feelings that gush from the deepest depths of the heart... right? Not quite. Actually, the real boss behind attraction is your brain, which runs through a very quick, very complex series of calculations when assessing a potential partner. Dawn Maslar explores how our five senses contribute to this mating game, citing some pretty wild studies along the way.

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.

Young black bears need to be careful when encountering the North American porcupine. Enjoy more footage from Alaska and Princess Royal Island in British Columbia, where young raccoons are also out and about.

"Help us to complete development of the Ocean Energy Turbine designed to replace Fossil Fuel and Nuclear Energy Dependence." Back this project and make the world a better place.

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!