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It contains every known species of animals, plants, fungi and even microbes on Earth. Described as 'the Wikipedia for evolutionary history', the list has more than 2.3 million species. One of the scientists who put it together is Karen Cranston, a researcher at Duke University in North Carolina in the United States. She has been telling Alan Kasujja about the work behind the 'Tree of Life'. (Picture: Lonely tree in a field; Credit: Thinkstock)