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Mary Leakey (1913-), palaeoanthropologist, seen here on site during excavations at Laetoli, Tanzania, in 1978. It was during this expedition that the famous Laetoli fossil hominid footprints were uncovered. This 40 metre trail dated from 3.6 million years and showed that hominids had acquired the upright, bipedal, free-striding gait of modern man by this time. Mary Leakey was married to the palaeoanthropologist Louis Leakey. (KEYSTONE/SCIENCE PHOTO LIBRARY/JOHN READER)