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Every person on earth comes from a long line of ancestors that goes back to the earliest humans. That means that if you don't have any kids, you'll be the first one ever in your line to not have kids.
Having said that, I would bet that a "line coming to an end" is a pretty common scenario. Even if the average couple has 2.1 kids, there are going to be families with 10 kids, and others with none. I wonder if anybody has ever collected stats on what fraction of people never have kids. Maybe it's something you can search for if you know what the right search term is.
The line doesn't go back to early humans. The line goes back to the the very "trunk" of the tree of life, a microbe known as LUCA - the Last Universal Common Ancestor.
Ancestry doesn't just run through the history of man, it runs through the history of all life on Earth.
I know a Luca. Nice guy. Horny as hell, but a nice guy
Sure, but at some point there was an ancestor who wasn't human enough to think of it as "a line".
... but you would still be descended from them. Directly. One could even say in a linear fashion.