something i found genuinely fascinating in one of my college linguistics classes (which i will preemptively note were all A While ago, so a) i may be misremembering the specifics and b) some of this may be out of date) is that infants literally aren’t equipped to speak before a certain age, and i don’t just mean in terms of brain development!
if i’m remembering correctly, at birth, baby’s noses, mouths, and throats are arranged and wired in a way that, loosely speaking, means that mouths are for eating, noses are for breathing, and the two functions don’t really cross over, in such a way that - crucially - makes it extremely difficult if not impossible for them to inhale their food. this is obviously really good news for infant survival - they don’t have the muscle control yet not to send food down the wrong pipes! the catch is that this comes at the expense of… call it some of the ‘machinery’ that allows for a lot of human speech, the stuff that’s more complex than what you can produce by, say, combinations of yelling and smacking your lips together, basically!
as baby gets a little older, this ‘machinery’ shifts around and starts settling into more adult forms, which gives them the literal physical tools to start making more complex speech sounds and lets them breathe through their mouth too, at the cost of now being more prone to inhaling something you’re trying to send to your stomach instead
fun side note that’s actually how this came up in class - this is actually one of the distinguishing features of humans as a species, and part of what set us apart from other early hominid relatives! if i’m remembering correctly, neanderthals didn’t actually have this machinery either, so while they would’ve been able to produce *some* speech, they would’ve been literally physically incapable of reproducing a lot of modern human speech! they also would’ve been very confused by how easy it is for us to breathe in at the wrong time and send water into our lungs, but, well, you win some, you lose some
basically, it’s not that babies only start communicating when they do because that’s when their higher functions come online and they learn how words and language work, it’s that that’s when the hardware to start using that knowledge comes online! if you give them other tools to communicate with, sign language or aac or what have you, you’ll generally find that they’re more than happy to use them to communicate their world to you a lot younger than you might expect!
(… mind, the underlying assumption that babies don’t speak before that point because that’s when their higher functions come online - that, to use the language of the post before me, that’s when their consciousness really comes online - definitely feeds into a lot of ableism around any number of speech-related and -adjacent disabilities, but that’s a whole other post)
