Forget monkeys as an important ancestor, it's fish that you really have to thank.
Most of the important biological innovations that we humans enjoy and take for granted came from fish. Check out Natalie Angier's write up in the New York Times.
Fish evolved the first hinged and muscular jaws and teeth with nerves, the better to eat big, fast and wiggly prey. And fish evolved the first defense against such powerful jaws, the first skull to protect that all-important brain, built from thousands of tiny, overlapping teeth.
Then there's our beloved heads, with paired sense organs. Yep, invented by fish. And fish have incredibly complex social and behavior patterns, perhaps rivaling the complex rituals of Junior High cliques.
So next time you see a fish say thanks. And don't feel bad about eating the fish after you say thanks, the fish would understand.