Michelle Trudeau

Bears do it; bats do it. So do guinea pigs, dogs and humans. They all yawn. It's a common animal behavior, but one that is something of a mystery.

There's still no consensus on the purpose of a yawn, says Robert Provine, professor of psychology and neuroscience at the University of Maryland, Baltimore County. Provine has studied what he calls "yawn science" since the early 1980s, and he's published dozens of research articles on it. He says the simple yawn is not so simple.

When Samantha Deffler was young, her mother would often call her by her siblings' names — even the dog's name. "Rebecca, Jesse, Molly, Tucker, Samantha," she says.

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Transcript

RACHEL MARTIN, HOST:

When someone does something utterly selfless, you might think, oh, they're just a generous kind of soul. But new research suggests altruism may be hardwired in the brain. Reporter Michelle Trudeau has more.

Four years ago, Angela Stimpson agreed to donate a kidney to a complete stranger.

"The only thing I knew about my recipient was that she was a female and she lived in Bakersfield, Calif.," Stimpson says.

It was a true act of altruism — Stimpson risked pain and suffering to help another. So why did she do it? It involved major surgery, her donation was anonymous, and she wasn't paid.

"At that time in my life, I was 42 years old. I was single, I had no children," Stimpson says. "I loved my life, but I would often question what my purpose is."

"The lion and calf shall lie down together," Woody Allen once wrote, "but the calf won't get much sleep."

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