Very simplified version…

But the most wrong part is they describe in group bias as “people like us” in a way that makes it sound like it’s people who are like you on an individual level

In group bias sets with whomever you see as a toddler, even if that’s just on episodes of Barney although obviously to a lesser effect.

It can change later, but eventually old age makes you revert back to earlier in/out group definitions.

It’s why integration is such a big deal. Humans need socialized just like any other animal and it’s best done when young.