Heh… I don’t know if you’ve seen this, but if you want to spend some time,,, https://waitbutwhy.com/2019/08/story-of-us.html is going through a similar journey right now.
You are kind of overselling the fictiveness of lineage. Its true that I don’t know if I will have any heirs or descendants. I don’t know that I will every find someone to make more people with. However, I do know that my ancestors existed. If they didn’t exist, then How did I get to exist? People don’t just jump out of the ground fully formed.
That you have ancestors, sure, that’s an empirical fact. That they are who they say they are… well, “fiction” is a strong word, but it’s a matter of faith. There’s plenty of stories about people who complicate “family lineage” by raising siblings’ and childrens’ and neighbors’ children as their own, or just outright lying about parentage. Or look at the idea of “combining families through marriage.” And if you go beyond the family unit, there’s plenty of examples of people who complicate group identities through travel and migration and conquest and flight, or again outright passing.
Most of us can have a lot of faith that at least the generations we met told us the truth, especially in the modern world where we leave a lot of records. But go back 100 years, or 1000, and we’re often just accepting family stories.
I actually came here to say that this is what those over-the-counter DNA surveillance database companies are selling (you know, “23 And Subpoena Me” and all them). They offer a picture of scientific truth behind (or instead of) those stories. But if you scratch the surface of their DNA sampling techniques, you’ll see that they’re selling a story about the accuracy of that genetic testing, and then they’re letting you make up your own stories about how that knowledge should impact your senses of self and group identities. Stories on top of stories. But they’re obviously filling some need for someone.