Born good? Babies help unlock the origins of morality

Can infants tell right from wrong? And if so, how would you know? Come to Yale's baby lab.

The youngest kids in the study will routinely choose to get fewer prizes for themselves just to get more than the other kid --

[Ainsley: I'll pick green.]

-- in some cases, a lot more.

Paul Bloom: The youngest children in the studies are obsessed with social comparison.

[Mark: So you get these seven. She doesn't get any.

Kendall: Yay!]

Paul Bloom: They don't care about fairness. What they want is they want relatively more.

But a funny thing happens as kids get older. Around age 8, they start choosing the equal, fair option more and more. And by 9 or 10, we saw kids doing something really crazy --

[Abby: Green.]

-- deliberately giving the other kid more.

Mark: Green or blue?

Maeve: Green.

They become generous. Chalk one up to society.

Lesley Stahl: They've already been educated?

Paul Bloom: They've been educated, they've been inculturated, they have their heads stuffed full of the virtues that we might want to have their heads stuffed with.

So we can learn to temper some of those nasty tendencies we're wired for -- the selfishness, the bias -- but he says the instinct is still there.

Paul Bloom: When we have these findings with the kids, the kids who choose this and not this, the kids in the baby studies who favor the one who is similar to them, the same taste and everything-- none of this goes away. I think as adults we can always see these and kind of nod.

Lesley Stahl: Yeah. It's still in us. We're fighting it.

Paul Bloom: And the truth is, when we're under pressure, when life is difficult, we regress to our younger selves and all of this elaborate stuff we have on top disappears.

But of course adversity can bring out the best in us too -- heroism, selfless sacrifice for strangers -- all of which may have its roots right here.

Paul Bloom: Great kindness, great altruism, a magnificent sense of impartial justice, have their seeds in the baby's mind. Both aspects of us, the good and the bad are the product I think of biological evolution.

And so it seems we're left where we all began: with a mix of altruism, selfishness, justice, bigotry, kindness. A lot more than any of us expected to discover in a blob.

Lesley Stahl: Well, I end my conversation with you with far more respect for babies. Who knew?