Fossil Hand Could Upset Notions on Human Evolution
By JOHN NOBLE WILFORD
Published: May 6, 1988
In a finding that could upset established ideas of human evolution, a scientist reported yesterday that fossil hands from a South African cave strongly indicate that the direct ancestors to early man were not alone in developing the ability to make and use tools.
If confirmed, the discovery could mean that toolmaking was not in itself the decisive evolutionary step in the rise of the human species, as is usually thought. The fossil hands were identified as belonging to a line of large primates, contemporaries of early human ancestors, that vanished into extinction more than a million years ago.
Analyzing the thumb and fingers of the hand of Paranthropus robustus, Randall L. Susman, an anatomist at the State University of New York School of Medicine at Stony Brook, said he found clear evidence of humanlike manual dexterity, including a well-developed capability for precision gripping and the potential for power grasping. He said the thumb was remarkably humanlike.
In a report in the new issue of the journal Science, Dr. Susman concluded: ''Functional morphology suggests that Paranthropus could have used tools, possibly for plant procurement and processing. The new fossils further suggest that absence of tool behavior was not responsible for the demise of the 'robust' lineage. Conversely, these new fossils indicate that the acquisition of tool behavior does not account for the emergence and success of early Homo.'' Common Ancestor of 2 Species
Paranthropus robustus, also known as Australopithecus robustus, is a species that evolved in parallel with the human, or Homo, line. The two branches descended from the common ancestor Australopithecus afarensis about three million years ago.
The best known afarensis specimen is the skeleton, called Lucy, that was found in Ethiopia in the early 1970's. Lucy was not a toolmaker, but by about 2.4 million years ago stone tools began to appear. The hand bones found in South Africa are dated at about 1.8 million years.
Specialists in early human evolution were cautious in their initial reactions to Dr. Susman's report. They agreed that the hand appeared to be capable of making and using tools. But they raised questions about whether the hand was indeed from the robustus species, and not Homo habilis, and whether Dr. Susman was justified in challenging the prevailing thinking about toolmaking's key role in evolution.
Donald C. Johanson, president of the Institute for Human Origins in Berkeley, Calif., the discoverer of the Lucy skeleton, said, ''The big question is, how can we be 100 percent sure these hands are not from a Homo individual?''
Dr. Johanson noted that the hand bones were remarkably similar to those of Homo habilis or erectus and were found in a cave along with fragments of Homo as well as robustus bones.
Dr. Susman reported that, since more than 95 percent of the skull fragments in the cave were attributed to robustus, ''there is an overwhelming probability'' that any one specimen recovered there would be from robustus samples. 'We Can Only Speculate'
Eric Delson, a professor of anthropology at Lehman College of the City University of New York, said: ''Assuming the analysis is correct, then we can no longer think of robustus as weird guys that hung out in the corners somewhere. But if they were capable of making and using tools, we still have to ask the question: Did they? We can only speculate on the answer.''
Some stone tools were found in the South African cave at Swartkrans, but there was no conclusive evidence that they were made by robustus. But Dr. Susman said the bone tools there showed signs of having been used for digging. The robustus individuals were mainly vegetarians and might have used tools for digging edible roots.
Fred H. Smith, a professor of anthropology at the University of Tennessee at Knoxville, said the findings were important because they alerted scientists against the ''wishful thinking'' of assuming that all stone and bone artifacts in African fossil beds were necessarily the product of early humans. Some tools are several hundred thousand years older than the earliest known bones of the Homo line, which began to appear in the fossil record about two million years ago. Despite the lack of direct evidence, scientists have assumed that the tools were made by early human ancestors whose bones had yet to be uncovered.
Dr. Smith said it was possible that, even if robustus was making tools, the human ancestors, with their larger brains, were perhaps able to produce more sophisticated tools and adapt them to greater uses, thereby gaining an advantage in the competition for survival. Discovery of Bones
The bones that Dr. Susman analyzed were discovered a decade ago by C. K. Brain, director of the Transvaal Museum in Pretoria. Puncture marks on the skulls indicated that the individuals were killed by leopards. The animals scurried to the safety of the trees to feast on the carcasses, dropping bones in the openings to the cave.
Dr. Susman said the most telling evidence of toolmaking capability was the thumb. Not only did it resemble a human thumb, he said, but indentations revealed the attachment points for the ''uniquely human muscle,'' the flexor pollicis longus. No apes, only humans and their early ancestors, have such a muscle, which functions to bring the tip of the thumb into contact with the index finger for precision grasping. Two fossil bones from hand of a large primate, Paranthropus robustus, show evidence of manual dexterity formerly associated only with direct ancestors of early man. Both are shown alongside their counterparts in human hand. The pollical distal phalanx (A), bone at the thumb tip, reveals attachment points for a muscle previously found only in the human line. The first metacarpal (B) is the bone at the thumb base. The muscle and metacarpal are key to precision grasping. Source: Dr. Randall L. Susman, State University of New York