Those on-the-prowl Mars robots — Spirit and Opportunity — are sending back extraordinary images and science data about the red planet and its history of climate and water. The tell-tale clues of water left behind hint that some spots on Mars did have a persistent wet look that might have been sociable to extraterrestrial creatures. While Mars scientists have their eyes focused on finding tiny microbes, the question remains: just how far along could martian biology, if any, have evolved?