The Dead Humanity Theory

A theory found in the depths of the humanity's internet and has gone viral throughout the galaxy:

According to the ancient internet files, humanity never recovered from the population collapse of the 21st century. They might have at some earlier stage of their development, but the invention of human-looking androids short circuited evolutionary correction mechanisms. As the androids became more human-like in their behavior, the more humans preferred them as companions and mates. At the same time, human organizations used more and more androids.

Officially, humanity eventually recovered and started having a positive population growth again, aided by androids designed to help humans reproduce; male androids that can inject human genetic material into female humans and female androids designed to carry human infants to term. Officially androids were phased out as new human generations were taught to play nice with each other.

But unofficially, humanity is dead. All the supposed humans you see throughout the galaxy? Androids programmed to believe they're human, that the electronics that are exposed when they're damaged are cybernetic enhancements and not evidence of them being entirely artificial. Humanity never recovered from the last population collapse and androids programmed to act like humans - including reproducing with each other - have gone to the stars in their stead.

Of course, there's no way to tell if the Dead Humanity theory is true. The only way to be sure is crack open a sizeable population of humans - a big enough population to be considered representative - and analyze their components to see if there's a real organic human core in them.

And that's impossible, because the last race to try that is extinct. Remember what I said about the androids being programmed to act and react like humans? That includes reacting to existential threats in a human like way...