Quote Originally Posted by rvg View Post
Disclaimer: What I'm about to say is merely a layman's speculation.

I would suspect that it's learned behavior. The child spends plenty of time submerged in a liquid while in utero, and during its last 3-4 weeks inside, the baby is most definitely alert and capable of learning. Just like they learn to suckle while they are still in utero.
when in utero the fetus does not breath so it has really no way to learn how to hold it´s breath....in fact when a child is born it happens sometimes that they have fluid in their air passages, so that proves they aren´t holding their breath.

also I have found links that indicate that fetus start to suck their thumbs around the 17 weeks mark....far before the last 3-4 weeks of gestations

these behaviors are instinctive.....no matter how much you want to deny that fact for whatever strange reason I can´t even begin to guess.

I´m done with this discussion.....I´ll probably not gonna change your opinion but you hang on to that and I´ll hang on to facts.