I'm walking around in the dark bumping into things, some sharp, some feathery...bah, already off track. I? "I" is a label for a remarkably complex system of systems, and no one knows what it is. But in defense of not knowing what "I" is, no one knows what anything is. Freud caricatured these systems as id, ego, and superego. Moving beyond that to things Freud didn't say, only the first of those also applies to non-human animals or to anything that happened before the appearance of human language.
The ego and the superego -- again, not what Freud said about them, just using his outline -- co-evolved with language. You could call them products of language or, simply, perhaps, language.
The ego is the product of the superego. The superego is the parent, the ego the child. The ego is a product of manipulation. The superego is parasitical. The child does as commanded, by language, and the parent gets what it wants. Power gets what it wants, in this case, by placing itself inside the host. The child's body does as the superego says, hence the term parasite.
The one that obeys survives. Girls are better at language acquisition. Coincidence? Maybe. Just speculating, but it would make sense.
Back to the first sentence...
The system of systems I call "I" is randomly colliding into other systems in the dark, formulating narratives as to what is what and what have you. Science is a system of the type we call method that helps us recognize patterns of colliding systems to which we are proximate, of which we are one, without ever understanding anything more. Every time pattern X, Y happens, but what is Y? "I" will never know.