Facebook founder Mark Zuckerberg may have taken an extended paternity leave after the birth of his daughter, but generally, American men do not take more than a few days. Ninety-six percent of American men are back to work within two weeks of a baby's birth.

"There might be some stigma attached," says Gordon Dahl, an economist at the University of California, San Diego. " 'What if I take paternity leave, will I not get the next promotion? Or will people think I'm not as connected to the workplace? Am I kind of signaling that I don't care about work enough?' "

Dahl studied leave policies in Norway, where a generation ago men took long paternity leave at the same rate as American men. Then, in 1993, Norway changed the law. After every birth, working parents still got eight months of paid leave to split among themselves, but four weeks were added just for dad.

"Overnight, paternity leave take-up went from about 3 percent to 35 percent of fathers," Dahl says.

To continue reading this article, which goes into changes happening in California, go to: http://www.npr.org/2016/02/08/...ing-other-dads-do-it