Actually, if the conditions are right, the probability that life will develop on a suitable world is fairly high. Mars and Earth have similar elemental makeup, similar masses (thus similar gravity), and both contain water, have atmospheres, and maintan temperatures within the liquid phase of water through much of the year. Mars is a bit on the cold side of the "habitable zone" but it is within it, so the odds of life developing have always been thought much higher than on, say, a Jupiter-sized gas giant orbiting a large, turbulent star in a ten day period. Truth is, we have no data on biogenesis (or lack therof) in any star system other than our own, and we don't know even remotely close to the actual probability of the development of life on a suitable world.