Certainly, a large part of our identity is socially created. Yet, at the same time, there is a pretty large kernel that's there whether or not we're in our usual social circles, whether or not we change our career, location, etc. And, for some, that kernel is more important than the socially-dependent aspects.
I'd add that some parts of that kernel override whatever environment we're in. A gentleman is still a gentleman in the gutter, as they say. Just because you're in the company of thugs doesn't mean you're going to define yourself as a thug.
So, while we certainly do adapt our behaviour to the role that we're presenting, it is ultimately just a role - not our identity.
Whether we decide to act like those around us, or different than them, is irrelevant. The article is saying that just having someone around us to interact with in some way is vital for our brain to even function.
Introverts still have plenty of social interaction -- maybe not in the small area of recreational socialization that gets so much attention from extroverts, but our society is still made up of a bunch of people. You have to interact with them to do much of anything.
This drew my attention in particular. Is this true for all people, truly, including devout introverts, or is it merely a generalization? Does it perhaps have varying degrees of applicability based on how intro- or extroverted someone is?