Whilst reading this, I was somewhat reminded of an old Stargate episode where they visit a planet with Neanderthals (seemingly) on it. They soon discover the more intelligent society that also lives on the planet and find out that the Neanderthals were once part of society, but, downgraded. Soon the Stargate team de-evolves also. Something in the air; a contagion that some seem immune to. The doctor soon works out a simple antihistamine is the solution and the team is saved! And all the Neanderthals turn back into their more evolved form and rejoin society.

I know it's not the same! But, I was just reminded of that episode. 😅