Watch Now: You can watch the new CBSN Originals documentary, "Replacing Humans: Robots Among Us," in the video player above. It will also air on CBSN on Sunday at 8 p.m. and 11 p.m. ET, and at 2 a.m. ET Monday.

Dr. Hiroshi Ishiguro is known as the godfather of humanoids for his years of work developing uncannily lifelike robots. He's succeeded in creating robots that look and move like people, and not only that, he's giving them a full range of capabilities that help them behave and learn like we do.

But it's not the machines themselves that fascinate Ishiguro — it's us.

"People think my motivation is to build a robot. But it's not true. My motivation is to understand what a human is, by developing humanoid robots," he says in the new CBSN Originals documentary, "Replacing Humans: Robots Among Us."

He draws an analogy to athletes in the Paralympic Games with high-tech prosthetic limbs.

"They don't have arms and legs, but they are using prosthetic arms and legs. Are they 100 percent human, or 80 percent human or 70 percent human?"

He answers his own question. Of course they're fully human.

And then he takes a leap. "That means that a flesh body is not a requirement to be human. …They can be a new kind of human, right?"

It's a compelling idea, especially in Japan, where a rapidly aging population and declining birth rate is creating a workforce crisis. Without enough people to fill jobs and care for the elderly, could robots step up to fill the gap? Could they even become, as the robotics engineer Dylan Glaas put it, "better than people"?

CBS News' Adam Yamaguchi traveled to Japan to explore why that country is on the leading edge of robot development and the many different ways these increasingly intelligent creations are being incorporated into everyday life.