Near the end of the film Mission to Mars part of the scene I remember from the first run in theatres included the theory that Martians sent their DNA to Earth billions of years ago. For some reason, the footage showing the evolution of the DNA into humans was cut. What gives?

There is no way to convert "Mission to Mars" into a very good or even a good sci-fi film, but editing out the sequence of the seeding of earth from Mars and the evolution that followed eliminated the single interesting idea in the film. The idiot editor that made that decision, which is the most egregious editing error I have ever seen or heard of, should be fired on the spot and given a job and tools--namely, a mop and a bucket--more suited to his talent and put to work as a janitor. Shame on USA Network!

Exactly. That sequence was the only reason I watched it for a second time.
It would be like editing "Rosebud" from Citizen Kane, or changing the feds guns into radios in E.T.
Oh yeah, someone did go PC on that one.