"Normal" matter makes up about 5% of the mass/energy content of the universe. From studying this 5% we have discovered 4 fundamental forces and numerous fundamental particles. When I read things about dark matter and dark energy it seems that each is assumed to be a single class of phenomena. This seems odd to me because I would expect the stuff we can't see to be just as diverse as the stuff we can. Is there a reason that we expect fewer varieties of dark matter and dark energy then we observe of visible matter and energy? Or is it just because it's pointless to speculate about variety when we can't yet detect any of it.