I dunno, my mom wasn't/isn't extremely selfish or selfless, just kina in the middle. My father died when I was quite young, but from what I can remember, he was in the middle too. I think my mom was too caught up in raising two young girls to think about herself. And I know, compared to other people's parents that I know quite well, that, compared to them, she is not selfish in the least. From the opposite side, my grandmother is completely selfless, does everything for everyone, loves everyone, puts everyone first.
So I have to disagree, at least with my (immediate) family, there are no extremes when it comes to selfishness and unselfishness.