Puzzling Out Man's Ascent

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natural selection favored those of his genus who could stand up; an erect position enabled them to see over the tall grass to spot and hunt their prey—and to see and escape the carnivores that preyed on them. Thus they were able to survive longer and produce more offspring, who shared their physical characteristics. After many generations of selection, the savanna-dwellers had evolved into upright-standing animals distinctly different from the forest-dwelling relatives they had left behind.

Though scientists have found practically no telltale fossils from the crucial period between 8 million and 5 million years ago, anthropologists speculate that some time toward the end of this period the hominid line split into the species Australopithecus robustus and africanus. There was also a third species, which some anthropologists believe branched off at the same time, and others think evolved later from A. africanus. Whatever the case, it is generally agreed that the third species was not an Australopithecus, but the first creature that could rightfully be called Homo—a man.

Scientists believe they are closing in on the time when this earliest form of man emerged. Fossil evidence shows the split that produced the first human must have occurred longer ago than 3.5 million years—the age of the oldest known Homo fossils, which were found in 1975 by Mary Leakey. Again, the rigorous demands of savanna living may have been responsible for the branching out. Australopithecus africanus, straining to augment its food supply in the flat grasslands, began to eat meat—probably obtaining it not by hunting, but by scavenging the kills left behind by large predators. Australopithecus robustus, on the other hand, continued to subsist largely on seeds and nuts. Both eventually died out, unable to compete successfully with the large predators or with Homo. who was coming into his own.

While his Australopithecus cousins foraged or scavenged, Homo habilis began to make tools and to hunt. Both actions accelerated his evolution. Toolmaking, which required reasoning and more complex neurological hookups, gave a survival advantage to the creatures with the biggest brains. That led to an increase in brain size. Hunting, with its emphasis on outwitting animals that were either faster, stronger or fiercer than the hominids that hunted them, also stimulated rapid brain growth. In addition, says Milford Wolpoff of the University of Michigan, it placed a premium on cooperation, strengthening the bond between members of the group and starting man on the road toward developing language.

These developments, probably more than any others, hastened the differentiation between man and earlier hominids. Explains Anthropologist Charles Kimberlin ("Bob") Brain of the Transvaal Museum in Pretoria, South Africa: "Meat eating and hunting were important factors. If you remained a vegetarian, the necessity for culture was not nearly as great." Richard Leakey too believes that hunting helped to make emerging man a social creature. Says he: "The hominids that thrived best were those able to restrain their immediate impulses and manipulate the impulses of others into cooperative efforts. They were the vanguard of the human race."

Still, doubts about the sequence of man's emergence remain.

Scientists concede that even their most cherished