FOR ALL THE ANCIENT skulls and prehistoric-stone tools that Mary Leakey chiseled out of the rocks of East Africa, what this accidental anthropologist will be best remembered for are feet. Feet prints, actually. One day in 1978, on the arid Laetoli plain of Tanzania, Leakey bent over an impression that looked as if it had been made by a human heel. With a dental pick and brush she painstakingly cleaned away the 3.75 million-year-old, hardened volcanic ash that encased the print. Three hours later, convinced that the print had indeed been left by human ancestors, she stood up. Lighting one of her trademark cigars, she announced, "Now this really is something to put on the mantelpiece."
Or in a museum. The 75-foot-long trail of crisp footprints had been made by three lithe hominids (members of the human family) who ambled across the volcanic plain at the dawn of humankind. One of them seemed to pause and turn left, briefly, before continuing north. This relic of a behavior from eons back brought the find to life in a way that mere bones could not. As Leakey wrote, "This motion, so intensely human, transcends time. A remote ancestor... experienced a moment of doubt." The find helped overturn the prevailing wisdom that the seminal event in human evolution was the development of a big brain. Instead, it was standing up, which freed the hands to make tools. Toolmaking stimulated growth in the size and complexity of the brain. "This new freedom of forelimbs posed a challenge," Leakey wrote soon after the discovery. "The brain expanded to meet it." And humankind was born.
Without Leakey, who died last week in Nairobi at 83, the family tree of mankind would have been quite short of branches. In 1936 she married African archeologist Louis Leakey after a scandalous love affair. He was 30 when they began their romance, she 20; he was married, she had been expelled from two convent schools. Though she was trained as an artist, as soon as she joined him in Africa she began making discoveries that would change the whole field of human evolution. In 1948, on an island in Lake Victoria, she uncovered a piece of the skull of a Proconsul, an apelike creature that is ancestral to both humans and apes and that lived some 25 million years ago. The find was the first to support Darwin's notion that Africa, not Asia, was the cradle of mankind. In 1959, in Tanzania, she found teeth and part of the jaw of an ancestor new to science. The 1.8 million-year-old creature, Australopithecus boisei, so captured the public's imagination that it secured essentially permanent research funding for the Leakeys. She and Louis, who died in 1972, discovered the scattered remains of Homo habilis ("handy man") in 1960. Actually, son Jonathan was the first to spy the fossil fragments; she habitually dragged along her three small sons to the dig sites.
By 1968 Leakey had broken with her headline-seeking husband and decamped to Olduvai Gorge in Tanzania, where she directed research. "We would do well," she wrote, to "spend less time in putting forward our own, personal interpretations" and more on adding to the fossil record. Luckily for science, she did just that.