Puzzling Out Man's Ascent

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most significant, the creature had walked upright. Its foramen magnum, the hole through which the spinal cord enters the skull, was not in the rear of the skull as it is in an ape or any other animal that walks on all fours; as with Neanderthal. Peking and Java men, it was far enough forward in the skull to indicate that the spinal column was usually in a vertical position and that the young primate had been bipedal.

In 1936 the skull of an adult Australopithecus africanus was unearthed from a mine at Sterkfontein, in the Transvaal. From it, Robert Broom reconstructed a creature similar to the one found at Taung—an ape-man somewhat more than a meter (3 ft. 3 in.) in height, with upright posture and human-like teeth but a low forehead and a small brain. Two years later Broom uncovered a new type of the southern ape a mile away, at Kromdraai. The creature, later called Australopithecus robustus, was heavier and larger than the earlier South African finds, and had bigger teeth, set in a nutcracker-like jaw.

Even more surprises were in store. After World War II, the radioactive carbon-14 dating method was developed by U.S.

Chemist Willard Libby. This was followed by the invention of the potassium-argon method. Both gave scientists techniques by which they could accurately determine the age of the strata in which fossilized bones were found, and sometimes the age of the bones themselves. Using these new tools, they have determined that Java man and Peking man, now classified as Homo erectus, walked the earth more than 500,000 years ago.

In the late 1950s the anthropological team of Louis and Mary Leakey—Richard's parents—began finding, at Olduvai Gorge and other East African sites, remains similar to those uncovered by Broom. They produced convincing evidence that the massive-jawed robustus, which weighed 45 to 67.5 kg. (100 to 150 lb.), existed in the region nearly 2 million years ago. In the same deposits, the Leakeys also discovered pebbles chipped to form sharp-edged implements—evidence that even so far back, man's ancestors knew how to make tools.

But who? For a time, many thought the finds showed that the hulking robustus had been intelligent enough to make tools. Then in 1961 Jonathan Leakey, another of Louis' sons, unearthed parts of a 1.8 million-year-old skull that failed to fit easily into the familiar Australopithecus mold. The creature's teeth were more manlike than those of Australopithecus and the brain was larger; whereas Australopithecus brains averaged 450 to 550 cc. in volume, the cavity of the skull found by Jonathan Leakey indicated that it had contained a brain measuring nearly 700 cc. That was considerably smaller than modern man's brain—which averages 1,400 cc.—but large enough to suggest that it had belonged to a being that fit ideally between Australopithecus and Homo erectus. Louis Leakey and his colleagues named him Homo habilis (handy man), because they believed him to be the manufacturer of the tools found in the vicinity.

But the skull raised a new problem. While anthropologists could accept the idea of man having evolved from Australopithecus, the evidence seemed to show that Homo habilis lived at the same time as his less advanced cousins. If so, could he have descended from them? Also, if several species of pre-men lived side by side, which one was really man's