My deepest held TBS Theory™ is that Indah and Sadie are Atypical, and Mark’s ability is essentially a post-evolution version of theirs. Mark likens his ability to a radar for Atypicals a few times, including in this exchange with Damien:
—so I don’t think it’s completely far-fetched to draw a link between him and the other characters who describe an ability to sense Atypicals.
I could make a stronger scientific case for it if I had a better understanding of epigenetics, but to throw in just a tiny bit of real world reasoning here, I do know there are tons of things that can lead to the same genetic material being expressed differently. That’s what I think is happening with these characters: they all have the same genes that code for an atypical radar/mimic ability, but various epigenetic factors lead to Indah and Sadie having a pretty low-key expression of it in the form of their “Atypical radar” while Mark has, obviously, a lot more going on.
That’s actually how I’d argue all atypical ability evolution works: the genetic material for an evolved ability is always there, but only Sometimes do the stars align for it to be expressed. I would definitely say the trauma Caleb experienced as a teenager played a role in how his ability changed down the line.
I don’t think this type of ability evolution is super super common. Beck kind of acts like it is (“the line between empath and mind manipulator is gossamer thin”) but quite honestly I think he is generalizing based on his one (1) experience.
Part of the reason I don’t think this is, like, a common and expected thing for all empaths is that for three seasons straight, we see Dr. Bright regularly meeting with a. an empath who is deeply concerned about manipulating people, and b. a true mind manipulator obsessed with finding someone like him. She never once mentions anything like the evolution Caleb experiences in The College Tapes, even in her private notes to herself. (Obviously I know the real-world reason for this is that when Lauren was first writing those early seasons she hadn’t yet decided that Caleb’s arc would lead where it does, but I’m trying to play within the fictional world here.)
And on top of that, Wadsworth actually does allude to something like ability evolution, when she says this to Green:
—establishing that such evolutions are on the AM’s radar to an extent, but as a relatively new and unexplored phenomenon. And she specifically places empathy into her category of abilities not worth studying, establishing that she is not aware of this empathy/mind-manipulation connection.
All of this to say: I think ability evolution is something that happens with multiple abilities, not just with empaths, and I think it’s something The AM knows only slightly more than nothing about.
I think the quickest argument against the theory that Mark’s ability is a version of Indah and Sadie’s radar would be that Mark seems to be the only person with his ability, while Indah and Sadie’s thing is more common, but I’d argue the evidence supports that:
Most people’s abilities don’t evolve. I think there are a lot more regular empaths out there than Caleb/Blackwell-style manipulators, and a lot more regular dream divers than ones who developed an ability to astral project, etc.
Joan and Ellie had never met or heard of anybody like Mark, but that doesn’t mean no one else like him is out there—-Joan and Ellie had also never heard of empaths evolving an ability to project emotions outward, but Beck had, years before it ever happened to Caleb. The AM doesn’t know everything there is to know about Atypicals, and a lot of Atypical people, both as individuals and as separate organizations/communities, make a point to avoid The AM’s attention.
So I think it’s completely reasonable to believe that a lot of factors in Mark’s life/environment led to him developing a mimic ability at an early age, while neither Indah or Sadie ever did. But someone could, theoretically, have a radar like Indah’s for years, and then later in life start to be able to mimic Atypical abilities, in much the same way that Caleb had an empath ability for years and later developed an ability to push emotions onto others.