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About three-quarters of elephant calls are inaudible to humans and now the bio-acoustic team at Cornell University, USA, plans to eavesdrop on low-frequency conservations. Scientist Michael Farraday's famous "Candle" lectures delivered at the British Institution in London (and published 1861). Prof Phillip Tobias explains why the Sterkfontein Caves near Johannesburg – where remains of 600 hominids have been found, including last year a 3.5-million-year-old skeleton – will become a World Heritage site.