Fascinating news about our ancestors from the New York Times…
PRINTS SHOW A MODERN FOOT IN PREHUMANS
By JOHN NOBLE WILFORD Published: February 26, 2009
Footprints uncovered in Kenya show that as early as 1.5 million years ago an ancestral species, almost certainly Homo erectus, had already evolved the feet and walking gait of modern humans.
An international team of scientists, in a report on Friday in the journal Science, said the well-defined prints in an eroding bluff east of Lake Turkana “provided the oldest evidence of an essentially modern humanlike foot anatomy.” They said the find also added to evidence that painted a picture of Homo erectus as the prehumans who took long evolutionary strides — figuratively and, now it seems, also literally.
Where the individuals who made the tracks were going, or why, is beyond knowing by the cleverest scientist. The variability of the separation between some steps, researchers said, suggests that they were picking their way over an uneven surface, muddy enough to leave a mark — an unintended message from an extinct species for the contemplation of its descendants.
Until now, no footprint trails had ever been associated with early members of our long-legged genus Homo. Preserved ancient footprints of any kind are rare. The only earlier prints of a protohuman species were found in 1978 at Laetoli, in Tanzania. Dated at 3.7 million years ago, they were made by Australopithecus afarensis, the diminutive species to which the famous Lucy skeleton belonged. The prints showed that the species already walked upright, but its short legs and long arms and its feet were in many ways apelike.
Studying the more than a dozen prints, scientists determined that the individuals had heels, insteps and toes almost identical to those in humans, and that they walked with a long stride similar to human locomotion.
The researchers who made the discovery, as well as independent specialists in human origins, said the prints helped explain fossil and archaeological evidence that erectus had adapted the ability for long-distance walking and running. Erectus skeletons from East Asia revealed that the species, or a branch of it, had migrated out of Africa as early as 1.8 million years ago.
The lead author of the journal report, Matthew R. Bennett, a dean at Bournemouth University in England, analyzed the prints with a new laser technology for digitizing their precise depths and contours. The tracks were excavated over the last three years by paleontologists and students directed by John W. K. Harris of Rutgers University in collaboration with the National Museums of Kenya.
Daniel E. Lieberman, a professor of biological anthropology at Harvard who studies the evolution of human locomotion but was not a member of the research group, said the prints established what experts had suspected for some time. Erectus, he said, “probably looked much like us, both walking and running over long distances.”
Although the discoverers were cautious in attributing the prints to Homo erectus, Dr. Lieberman and other experts said in interviews that it was highly unlikely they could have been made by other known hominid contemporaries. “The prints are what you would expect from the erectus skeleton we have,” said Leslie C. Aiello, president of the Wenner-Gren Foundation for Anthropological Research, which supported the research.
William L. Junger, a paleoanthropologist at Stony Brook University in New York, said the footprints were further evidence that erectus had “undergone a major structural change in body plan, and it’s much like our own.” One obvious exception: the erectus brain, which was more advanced than those of previous ancestors, but was still much smaller than the Homo sapiens brain.
No erectus foot bones have been found anywhere, but other well-preserved, yet incomplete, skeletons showed the species to be taller and less robust than earlier hominids. The strides of these footsteps suggest that the individuals were an average of 5 feet, 7 inches tall; one, presumably a child, was 3 feet tall.
The site of the discovery is about five miles east of Lake Turkana, near the village of Ileret, in northern Kenya.
Dr. Harris of Rutgers said that excavations from 2005 through last year yielded scores of animal tracks as well as the erectus footprints. Geological evidence indicates that they were made on the muddy surface of a floodplain in a time of nearby volcanic eruptions. Layers of volcanic ash, mixed with silt deposits, were examined to date the finds.
The tracks were confined to two layers of sediment, vertically separated by 15 feet and about 10,000 years. The upper layer contained three footprint trails, two of two prints each and one of seven prints, as well as several isolated prints. The lower layer preserved one trail of two prints and a single isolated print.
Dr. Bennett joined the project in 2007 to make three-dimensional digital records of the footprints. He also scanned the tracks of local people who walked through soil from the excavations. He said their prints, like those of other modern humans, were remarkably similar to the erectus prints. Later, digital images of casts of the prints from Laetoli showed marked differences in foot shapes.
Anatomists analyzing the Ileret prints said the heel, instep, balls of the foot and short toes were considerably distinct from the prints discovered in Tanzania and almost identical to modern humans. Most obviously, the big toe is in line with the rest of the toes, not angling away from other toes, as on an afarensis foot.
The footprints discovered in Kenya, researchers said, indicated that the erectus foot functioned much as a human foot does: the heel contacts the ground first; weight transfers along the arch to the ball of the foot; and the push-off is applied by the forefoot. In apes and apparently earlier hominids, this force comes from the midfoot.
The discovery is “even more explicit evidence,” Dr. Harris said, that the erectus species extended its range into more diversified habitats, camping and discarding stone tools at sites far from the sources of the stone.