Well, they gotta posses demonstrable competence in the fields but the question becomes, "Will they grow and bloom?"
IMO you are looking for both aspects and not just the former.
Does that make sense?
Discussion
I think that's where it gets really tricky.
Superficially, just by looking at the resume you can't really make out if the candidate has the desire to learn.
You have to find that out in the interview but a really good candidate should've made mention of a desire to 'grow' in the cover letter.
This is just my opinion but I believe it applies to any job including welding, computer programming, or nuclear physicist.