Echolocation is second nature to animals such as bats and dolphins. Can humans also find their way using sound as a tool? Ian Waldie/Getty Images hide caption

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Johnson with her fellow researcher and sometimes husband, William Masters. The pair helped legitimize the study of human sexuality. AP hide caption

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Anton-Marlot/iStockphoto.com

The next time you are in an office cafeteria, notice who sits next to whom at lunch. Jose Pelaez/Corbis hide caption

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It's busy down there: a gut bacterium splits into two, becoming two new cells. Centre For Infections/Science Photo Library/Corbis hide caption

itoggle caption Centre For Infections/Science Photo Library/Corbis