The evidence and predictions surrounding our ability to extend our lifespans and solve life- and existence-threatening problems is enough to suppose that the human history is not closed at the far end, or not modeled on the same function that pre-actuarial-escape-velocity human history is.

That is, we have good reason to believe we are in the earliest of all humans, because "human" is two sets appended together, and the doomsday argument is based on the statistics of the first set alone.

That is my response to the doomsday argument - I don't know if it's rigorous.