or does their study only seek to confirm their preconceptions
I'm sorry, but this must be one of the absolute stupidest things you could say on this forum. Almost every single person on here used to reject evolution. Our preconception was that evolution was FALSE!
It was only because of evidence based arguments that we changed our minds!
And I really don't know what to say here, it's like someone asking me, "What are the holes in the theory of gravity?"
"What are the holes in Atomic Theory?"
"What are the holes in Cell Theory?"
As far as I know, there aren't any holes in any of these. Or in evolution. And if I could find a hole in any of them, I would write a peer reviewed paper on it and win myself a Noble Prize!