Purpose of the Moro Reflex?

[Hermitian]

Moro Reflex. I came about this term when reading fetal development literature.

Apparently it is good for checking motor system stuff after a baby is born.

But why? Why do babies do this? Is there some kind of benefit or is it completely worthless (to the baby)?

[groman]

There’s a chance it’s purposeless – an artifact of some other reflexes. I do not know what other animals show the moro reflex, so it could’ve made more sense in whoever developed it first (and then again, it might’ve been pointless then). This sort of thing wouldn’t necessarily get weeded out by selection because it looks fairly non-harmful, so it could’ve just stayed without providing a particular benefit.

Assuming it has some benefit, I’m going to throw a complete WAG out there and say that it roughly follows the correct sequence of things an infant should do if they were about to fall.

1. Spread out the arms to allow for more opportunities to be grasped by an adult before falling
2. Tuck in the arms to reduce injury from a fall
3. Cry, cause they just fell

[don_t_ask]

@groman

There’s a chance it’s purposeless – an artifact of some other reflexes. I do not know what other animals show the moro reflex, so it could’ve made more sense in whoever developed it first (and then again, it might’ve been pointless then). This sort of thing wouldn’t necessarily get weeded out by selection because it looks fairly non-harmful, so it could’ve just stayed without providing a particular benefit.

Assuming it has some benefit, I’m going to throw a complete WAG out there and say that it roughly follows the correct sequence of things an infant should do if they were about to fall.

1. Spread out the arms to allow for more opportunities to be grasped by an adult before falling
2. Tuck in the arms to reduce injury from a fall
3. Cry, cause they just fell

That makes a lot of sense. Many things that kids do now seem weird but presumably work like that.

When my son was about 3 or 4 he slipped off a rock and fell in to a river. I jumped in and grabbed him but what amazed me was that he was floating under water with his arms spread and his eyes open and seemed totally relaxed. As soon as I pulled him out he became active and began to cry.

I researched what had happened and discovered that it is the reason so many children drown in backyard pools. They don’t thrash around and attract attention, they just quietly drown.

[njtt]

Well, it is awfully cute… (That’s a survival advantage.;))

I am dubious about groman’s theory because they do it to a sudden loud noise (or, I think, anything that startles them) as well as to falling.

Anyway, I question the implication in the Wiki article that it disappears completely in normal older children and adults. It may get overlain by other behaviors, but it is recognizably akin to things adults do when startled. When I noticed that my baby daughter did it (at which time I had no idea that it was a scientifically recognized reflex) I dubbed it her “good gracious!” gesture, because it did indeed look like a stereotypical adult expression of surprise. (Once, when she was falling asleep in her high-chair and there was a sudden noise, she did it in slow motion.)

My WAG is that its function is communicative. They are telling the parent that they have been surprised rather than doing anything directly about it themselves. (In my experience with my children, it was by no means invariably followed by crying, which conveys a somewhat different message. Crying means they want you to do something to make them feel better. The Moro/startle gesture is simply telling you that they have been surprised.)

[njtt]

Incidentally, I discovered this on the Wiki article’s discussion page

Originally posted by Wikipedia editors:
“The origin of this reflex can be found in that fact that primate infants of our ancestors clung to their mother’s fur soon after birth…” [emphasis mine]

Is the infantile behaviour of our primate ancestors so conclusively known that it can be stated as a fact? Certainly existing primates exhibit this behaviour and we can infer that our ancestors behaved similarly, but is it known how our ancestors acted? Perhaps this should be reworded or at least a citation should be provided. Clayton Rumley 03:27, 2 March 2007 (UTC)
I agree, and I’m going to change it. - Paul

There is at least a hint of a plausible explanation there, even though the editors seem to have removed it for being too speculative. I suppose the idea is that the baby monkey, when startled, reflexively reaches out to grab onto its mother.

[Joey_P]

@don_t_ask

I researched what had happened and discovered that it is the reason so many children drown in backyard pools. They don’t thrash around and attract attention, they just quietly drown.

We had a thread on that not to long ago. Several people posted exactly that same thing. Parents expect to notice if their kids are drowning, and I don’t blame them, I didn’t know better until I read that thread. Seems like one of those things we could use some education on. Just a little snippet here and there on the news when pool season starts in summer.