Extras

Video thumbnail: Nature Hard-Wired?

Nature

Hard-Wired?

Genetics and brain physiology can affect a dog's personality and behavior.

Hard-Wired?

Video thumbnail: Nature Dogs That Changed the World (Part 2) - Preview

Nature

Dogs That Changed the World (Part 2) - Preview

Airs Wednesday, October 9, 2011 at 8:00 p.m. ET/PT. Check your local listings.

Dogs That Changed the World (Part 2) - Preview