system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel] What is the difference between mutants and Inhumans?
gpt
Every human line on Earth eventually will be mutant. It's latent in our biology, put there by the Celestials in pre-history. 

The first, rare mutants, began activating thousands of years ago. By the year 2000 there were millions of active mutants, but millions were killed in the Genosha apocalypse. Eventually more will be born. It's an inevitability. 

Something in the 20th century -- probably not atomic weapons, maybe -- vastly accelerated the pace. Maybe it was planned. 
Eventually there will be no baseline humans, in so many generations. 

Inhumans are another fork of humanity. ALL Inhumans are mutants, but their powers do not naturally activate. Exposure to a substance called Terrigen mist in moments fully mutates them to whatever they are meant to be. An Inhuman who lives his life without at least one exposure to Terrigen biologically functions as a normal human, but with special DNA. 

It's been implied everyone in Marvel who gets powers from odd exposures to things, like the Fantastic Four, Spider-Man, the Hulk, Daredevil, etc, are like that because of something unique but unknown in their own lineage, tracing back to Celestial meddling.