We are talking about different time scales and different conditions. Life on Earth only became multicellular and complex in the last billion years or so. Before then the big evolutionary advances were the formation of various organelles, the formation of the cell nucleus, and the formation of DNA from RNA. The formation of DNA is what allowed single celled organisms to mutate and diversify. But it took a very long time.
On Mars we have a different situation. Life could have existed planetwide from about 3.5 billion years to 3.0 billion years (when the planetary magnetic field failed and the solar wind started stripping the atmosphere eliminating liquid water on the surface). It took almost 2 billion years for DNA to form on the Earth with the ability of organisms to survive around the planet. Mars had about half a billion years before the planet froze over. If life existed on Mars it does so in very small isolated quantities where liquid water can be found.
But you realize we are talking about evolution here.. and evolution conqueors all....