Word: bacteria
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...proposed that natural selection could gradually transform a species. Scientists have observed thousands of cases of natural selection in action. They've documented that beaks of finches on the Galápagos Islands have gotten thicker when droughts forced the birds to crack tough seeds to survive. They've observed bacteria develop resistance to drugs that were believed to be invincible. Now biologists are applying DNA-sequencing technology to natural selection, which lets them identify the individual genetic changes that boost reproductive success...
...there's more to the history of life than the branching of a tree. Every now and then, DNA moves between species. Viruses ferry genes from one host to another. Bacteria swap genes inside our bodies, evolving resistance to antibiotics in our own gut. Some 2 billion years ago, one of our single-celled ancestors took in an oxygen-consuming bacterium. That microbe became the thousands of tiny sacs found in each of our cells today, known as mitochondria, that let us breathe oxygen. When genes move this way, it's as if two branches of the tree of life...
Biologists have documented a vast amount of gene-swapping among single-celled organisms - which happen to make up most of the diversity of life on Earth. There are 10,000 species of bacteria in a spoonful of dirt, twice as many species as all the mammals in the world. In the genome of a typical microbe, most of the genes hopped from one species to another at some point in the history of life. In some ways, the history of life is indeed like a tree, sprouting new branches. But in some ways, it's also like a tapestry, emerging...
...room to minimize bacterial contamination, and its arm, which would have direct contact with Martian ice, was heat-sterilized before launch, it's likely that dozens or more species of microbes hitched a ride on Phoenix's 10-month trip to Mars. Once on Mars, it's possible that bacteria shielded by the structure of the spacecraft from the harsh Martian UV radiation could stay alive, in dormancy, for hundreds of thousands of years. And if native microbes do exist on Mars - nothing has been found yet, but scientists hold out hope that the ice present on parts...
...Mars, "contamination by even one Earth bacterium may be a serious issue of environmental ethics," McKay writes. We only have to look back at the damage that invasive species have inflicted on virgin territory on our planet, like the infamous cane toads that ravaged Australia, to know what Earth bacteria could do on an alien surface. (See pictures of Mars' surface patterns...