I know the colonial fleet is referred to as being human, but now that we have some evidence that Earth is very much our Earth, we have to consider which race of people is our people.

It seems there are at least three (possible four) races of "people": the "humans", the 7 cylons, the Four, and the One. Which of these makes up humanity as we know it? The human mind seems accessible to the cylons, so perhaps the humans are in fact part cylon. If the Earth people (assuming we find some - I think we will) are actual people, then the fleet is most likely something else.

I do not think that the Four are Earth-humans, but I think the One might be. Prior to seeing Razor, I theorized that the human-cylons did not evolve from the centurians at all but rather re-enslaved them. Although that no longer seems possible, I'm open to the truth containing similar components, such as that the cylons themselves are collaborated race.

As for the song, I think that the lyrics are definitely significant:
"There are many here among us
Who feel that life is but a joke
But you and I we've been through that
And this is not our fate
So let us not talk falsely now
The hours getting late"

This seems to indicate that the final cylons do in fact die, and will die soon.