DAJBThose poor timelords :(
It's a tricky business, all that "wibbly-wobbly, timey-wimey" type stuff. If your jumping on point is anywhere within the last five series though, the starting assumption is that the Doctor is the last!
In the original series there was this whole thing about earth's population being a sort of second try at human civilisation... in that there was some big galactic federation of space-going humans in the past at some stage and then that was all destroyed by some old disaster in the forgotten past. Is that still a thing in the show or do they just ignore all that sort of thing from the older series?