It’s not a theory.
DNA doesn’t lie.
after 8 generations it becomes academic.
go far back enough and all are genetically related.
Field-Jefferson-descendant DNA, not necessarily Thomas-Jefferson DNA.
Actually the DNA from the supposed descendant of the Hemings child conceived in Paris -- when Thomas was the only Jefferson in the vicinity -- turned out NOT to have any Jefferson DNA. Also there were other times when Thomas and Sally were at the same place, and could have conceived a child (no birth control back then), but no child was conceived.
Monticello was often closed up when Thomas Jefferson wasn't there. It's only natural to assume that visits from other male Jeffersons would take place when he was there. So it's not surprising that conception dates match those presences (but, interestingly enough, not the one when he and Hemings were too far away for other Jeffersons to visit -- in Paris).
You state that Randolph was not at Monticello when some of the children were conceived. I’d have to see very convincing proof to believe that (preferably from sources with no political agenda). Even if true, though, there’s no reason to assume that all her children had to be fathered by the same Jefferson. For that matter, any slave in the vicinity who was fathered by a Jefferson — in that generation or a previous one — could have passed on Jefferson DNA to a Hemings child.
I think the proper attitude on this matter is extreme skepticism. Though the modern charge had been brought up earlier by the black historian, it wasn’t until the Clinton-Lewinsky scandal that a concerted effort was made to use it to discredit Thomas Jefferson (in an attempt to show that Bill Clinton wasn’t so bad after all). In the historical article that accompanied the publication of the DNA findings in the journal Nature, Joseph Ellis explicitly made the connection with Bill Clinton. (Ellis, by the way, was the Jefferson biographer whose lying about having served in Vietnam was later exposed.).
I don’t rule out the possibility that Thomas Jefferson fathered some of the Hemings children, but don’t trust the persons whose interest it is to make that claim. It hasn’t been proven to my satisfaction yet.
I followed the story closely in the early years, but haven’t been following it closely lately. Here’s a critical analysis, though, of the Research Report on the Jefferson-Hemings Controversy — https://jeffersondnastudy.com/rebuttal-to-tjmf-report/ . If you have very specific facts that can refute those objections, which can be confirmed in an objective way, I’d be interested in seeing them.
Until then, my position is that it’s possible that Thomas Jefferson was the father, but absent a finding from Maury Povich, I still remain skeptical. :-) There have been far too many attempts to demagogue this question for me to take such claims at face value.