It's a question people have asked for as long as there have been people: are human beings inherently good? Are we born with a sense of morality or do we arrive blank slates, waiting for the world to teach us right from wrong? Or could it be worse: do we start out nasty, selfish devils, who need our parents, teachers, and religions to whip us into shape?

The only way to know for sure, of course, is to ask a baby. But until recently, it's been hard to persuade them to open up and share their secrets. Enter the baby lab.

This is the creature at the center of the greatest philosophical, moral, and religious debates about the nature of man: the human baby. They don't do much, can't talk, can't write, can't expound at length about their moral philosophies. But does that mean they don't have one? The philosopher Rousseau considered babies "perfect idiots...Knowing nothing," and Yale psychologist Karen Wynn, director of the Infant Cognition Center here, the baby lab, says for most of its history, her field agreed.

Lesley Stahl: Didn't we just think that these creatures at three months and even six months were basically just little blobs?

Karen Wynn: Oh, sure. I mean, if you look at them, they--

Lesley Stahl: Yeah.

Karen Wynn: They kinda look like little, I mean, cute little blobs. But they can't do all the things that an older child can. They can't even do the things that a dog or a pigeon or a rat can.

No pulling levers for treats or running mazes for these study subjects. But they can watch puppet shows. And Wynn is part of a new wave of researchers who have discovered seemingly simple ways to probe what's really going on in those adorable little heads. We watched as Wynn and her team asked a question that 20 years ago might have gotten her laughed out of her field. Does Wesley here, at the ripe old age of 5 months, know the difference between right and wrong?