[coretx]

Ehw,no. The ego ( the prime source of identity ) only enters existence when we first encounter another. And even then, it's nature constantly differs, instigated by it's surroundings. In a nutshell, your "Us" and "Them" usually differ from mine and often mutates. Essentially, this makes divide et impera & us versus them thinking even more stupid as we humans have "theory of mind" for a trait. Unlike many animals. https://en.wikipedia.org/wiki/Theory_of_mind

Edit: So it's a cultural rather than biological precondition. ( If a precondition at all. )

[bildung]

I'd say both you and pdamoc are right :)

For us being able to develop and change Ego and Alter, we need to have the mental capability for doing so. Which we obviously have, physically.

Both Ego and Alter can and do change heavily through life, and thus are strongly affected by culture, socialization etc. They can't change unbridled, though: There are multiple facettes of personality that are pretty stable over time (like in the Big Five model), ignoring traumata etc. And there are limits to our mental capabilities, just like there are for reasoning and other aspects of mind.

So, within the pysical borders our bodies give us, Ego and Alter can develop quite freely, heavily mediated by culture.