[dusted]

I don't agree entirely. Our physical bodies may not have changed much (also not entirely true but a different discussion). But the fabric of thought and knowledge has changed immensely. When a human is born today, to caring parents, they will have entirely different experiences, stories, teachings than their 1000 year old counterpart, and these shape their brain and mind immensely. What is "human nature" if not what we become as we grow? Even our instinct to survive has changed, and is very varied (from survivalist trump types to hippies and beyond probably).

There's no reason to debate "who would survive if the world was so-and-so" it's interesting, but not important in discussion what human nature means.

So, let's swap people from today and the earliest homo sapiens: Newborns with type 1 diabetes - Only the one from the past survives 5 year old healthy kids: - They'd probably do fine, assuming the one from today can adapt their immune system (and vice-versa). 10 year old healthy kids: - Probably already issues here, I'd not bet on the modern kid. 30 year old person: - Not betting on the modern one, might be they can integrate themselves into the group, but it might become apparat that they're not carrying their weight, and ousted. - The one from old, if they manage to learn our language, that'd be success, they'd probably end up in prison or an institution.