Why haven't we observed mutations of new body parts?

I saw a program on television showing just that. Scientist took
a simple celluar organism changed one gene and it changed instintly in the next generation. This creature had an primitive one valved heart and the scientist changed a gene and the next had a two valved heart.This proved that evolution can be quik. Personally I think we has humans have evolved to a point that we don't any extra arms. Evolution is all about changing to survive and we are the most succesful species on the planet. So don't think we are going to
grow wings any time soon. Try to Google that experiment I can't
remember the program it was on.