Partnerships

It's weird how we often remember only one person out of a partnership. Why is it that one person can get everlasting fame/notoriety and the other just sinks into oblivion?

Case in point:
Marx and Engels. We don't call it Engelism, do we?
Darwin and Wallace. Again... it's Darwinism.

Well, Marxism and Darwinism sound a lot better, there's not doubt about that. But still, don't you feel bad for those partners who will never go down in history, who will only be studied by scholars/students of the field but will never be truly recognized by the general public? I mean, I could ask my mom, who knows almost nothing about politics/philosophy about communism and she would say "Marx" off the top of her head. And I could ask an art major about evolution and he would say "Darwin." It's just a little unfair, n'est-ce que pas?

Edit: one partnership which I think has gotten equal recognition is Watson and Crick (DNA double-helix, won the Noble Prize, etc.). But do people really know who they are? (beyond Bio majors and scientists and all that). I mean... I don't know. But at least they're equally semi-famous.