There was a recent media kerfuffle about MOND (Modified Newtonian Dynamics), an alternative physical theory that supposedly eliminates the need to have dark matter be a major part of the universe.

• Findings Raise New Questions About Dark Matter
• Dark matter theory challenged by gassy galaxies result
• More Evidence Against Dark Matter?
• Dark Matter: A Ruling Theory with no Clothes?

However, as Ethan Siegel and Sean Carroll pointed out, this alternative theory only works for one set of observations that are explained by dark matter. There are others about which MOND has nothing to say.

• Good ideas, Bad ideas, MOND, and Dark Matter
• Dark Matter requires you to THINK BIG!
• Dark Matter: Just Fine, Thanks

Hence dark matter explains much more than MOND, and for that reason alone is to be preferred as a physical theory.