In a controversial paper by a Russian-American team of researchers, it is has been claimed that incredibly hardy microbes with an extreme resistance to high levels of radiation may have evolved on Mars. The argument goes that at no time in the Earths history has there been an evolutionary need for such extreme resistance, which is rated at several thousand times the lethal doze for a human being. It has already been demonstrated beyond reasonable doubt that some meteorites found on Earth had originated on Mars (they were themselves likely blasted from the Martian surface during cataclysmic meteor impacts) and given that the evidence for water on Mars keeps coming on thick and fast, it is not a great leap to imagine some of these super bugs surviving the trip to Earth. Deinococcus radiodurans is one such microbe, and in honour of its toughness, has been nicknamed "Conan the bacterium" by microbiologists. But not all scientists agree with the theory, with a counter argument raised that the radiation hardiness is simply a side effect of the microbes developing a resistance to dehydration. The BBC News site has more on this story.