By John Noble Wilford
Thursday, 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 published Friday in
the journal Science, wrote that the well-defined prints in an eroding
bluff east of Lake Turkana "provided the oldest evidence of an
essentially modern humanlike foot anatomy" and added to the 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 for
leaving a mark as 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, sometimes called "fossilized behavior," are rare indeed.
The only earlier prints of a protohuman species were found in 1978 at
Laetoli, in Tanzania. Dated at 3.7 million years, 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 erectus prints, scientists determined
that the individuals had heels, insteps and toes almost identical to
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 was Matthew Bennett, a dean at
Bournemouth University in England, who 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 Harris of Rutgers University in
collaboration with the National Museums of Kenya.
Daniel 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, 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 Aiello, president of the Wenner-Gren Foundation for
Anthropological Research, which supported the research. "We are seeing
erectus in motion," she added.
William 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, though advanced from
previous ancestors, was still well below the size of the Homo sapiens
brain.
No erectus foot bones have yet been found anywhere, but other well-
preserved skeletons showed the species to be taller, less robust than
earlier hominids.
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