Being with your dog makes you feel good. Dr. Barker is trying to find out why. She studies what happens inside our bodies when we interact with therapy dogs.

Their brains of these robots are still no more advanced than that of a one-year-old, but scientists want to bring them up to the level of a teenager. At least.

Astronauts in space can lose about as much bone in a month as a senior citizen loses in a year on Earth, said Bateman. Read more on bone loss therapy.

How does the 2010 U.S. Census count homeless people and immigrants who might be afraid of being deported? Read the answer here.

Susan Burns, CEO of Global Footprint Network, explains how the 'ecological footprint' can make businesses - and the world - more sustainable.

My Earth Day guilt trip through the Ecological Footprint quiz, and out the other side.

The U.S. census it a great resource to look at population change," said Mather, "not only at the national level, but the regional level, state level, and to see what's happening in local communities all the way down to the city block level."

Use of wind power is on the rise, Sawyer said, as governments all over the world consider how to generate more electricity and emit fewer of the greenhouse gases thought to be warming the planet.

"Creativity is critically important for sustainable business," said Robert Epstein, "in part because sustainability is a goal that has a deadline." Read more.

Marvin Odum, president of Shell Oil, gives Shell’s perspective on the most immediate solutions to climate change and the role the U.S. should take.