> Grad students making significant contributions is extremely rare; basically all of the real research is done by tenured professors.
...but most of these first authors (the people formally credited with doing the real work) are graduate students, so how does that fit in with your theory?
Well i think it just depends on how 'significant' you need the phd to be. As an example of what I mean, consider the first issue of this years Annals of mathematics [1] and note that there is not a single grad student on any of the papers, first author or otherwise.
...but most of these first authors (the people formally credited with doing the real work) are graduate students, so how does that fit in with your theory?