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2014-05O'LearyFp191.jpgClick to Enlarge Image A kangaroo, a cat, and a duck-billed platypus are all recognizable as mammals, although the process of gestation takes a different form in each. At what point in evolution did our own subgroup of mammals begin to develop a placenta? O’Leary describes the vast stores of information that genomic researchers and paleontologists bring to bear on such a question, and the new tools in software that promise to make sense of it all.

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