There are some theories of gravity which explain it as emerging from other fundamental forces. To better understand the evidence for and against these theories, I would like to have a better understanding of evidence for the mainstream assumption that gravity affects all particles to a degree which is proportional to their mass.
Obviously, most of our observations of gravity measure its influence in attractions between large objects consisting of atoms.
Now, in an answer to the question of whether subatomic particles are affected by gravity, Alan Rominger describes experiments which appear to have isolated the influence of gravitaty on ultracold neutrons. That is very interesting.
But assuming these results are correct, it seems consistent with current evidence that gravity might be a weak attraction between hadrons (protons and neutrons), not affecting other particles.
Do we, for example, have direct evidence that gravity affects electrons? (Please don't say "the Millikan oil drop experiment"!)