Capetown and the South African Footprints

The earliest fossilized footprints of an anatomically modern human have been discovered in 117,000-year-old sandstone on the shore of a South African lagoon. Fossilized bones may inspire paleontologists and a particular type of DNA may satisfy geneticists who have traced modern Homo sapiens back to a certain time in Africa.

However, for everyone else, a trail of footprints has proven to be more tangible. The new discovery is particularly welcome in the study of human origins because the fossil record is woefully incomplete for the period when archaic Homo sapiens evolved into the modern species. Most paleoanthropologists, and especially geneticists, believe this fateful transition occurred between 100,000 and 200,000 years ago. Geneticists think the "African Eve," the one common ancestor of all living humans, lived at about this time. Only about 30 ancestral human fossils and no other footprints from that period have been found anywhere in the world, most of these were in southern Africa. Dr. Lee Berger, who led the research team making the discovery, said, "These footprints are traces of the earliest of modern people."

The most famous ancient footprints, made some 3.5 million years ago, were left by two adults and a child, presumably members of the Australopithecus afarensis species, who walked across a plain now known as Laetoli in Tanzania. The long track of prints was discovered in the late 1970's by an expedition led by Dr. Mary Leakey, the noted Kenyan paleontologist. The prints provided further evidence that human ancestral species were walking upright long before they started making stone tools. Other known prehuman footsteps were left 1.5 million years ago by Homo erectus, a predecessor species, at the Koobi Fora Site in Kenya.

Until now, no one had found any tracks of modern humans from 100,000 years ago. Dr. David Roberts, a South African geologist, was the first to lay eyes on the three footprints in rock within 20 feet of the edge of Langebaan Lagoon, about 60 miles north of Cape Town. He was acting on a hunch. He had been picking up rock fragments that had apparently been chipped by human ancestors. And the surrounding gray sandstone was marked by animal tracks. Hundreds of people had walked over that area, including scientists, and not noticed the prints. The human track extended only five feet, before disappearing at the base of a stone wall. Two of the prints are well preserved, revealing in detail the shape of the individual's big toe, ball, arch and heel. In every aspect, Dr. Berger said, these were the prints of modern human feet. The big toe was longer than the others, a trait known as the Egyptian toe. For many people today, the big toe is the same length or slightly shorter than the next toe. In the process, several different dating techniques were applied in analyzing the rock bearing the prints, and they all agreed on an age of 117,000 years, give or take a few thousand years.

Judging by the length of the stride and the foot size, eight and a half inches long, the individual was no more than five feet six inches tall, probably shorter. Scientists said the person could have been a female or a juvenile or a small male. Not much to go on, but enough for scientists to conjure up a gossamer image of the long-ago moment. Soon after a rainstorm, an individual walked down the slope of a dune, approaching the lagoon at an angle and leaving tracks in the wet sand. Was this a casual stroll, or someone combing the beach for food washed up by the storm? Nothing in the steps betray purpose or destination. But when the dune dried out, wind filled the footprints with sand, protecting them for eventual petrifaction and then for its discovery.

After finding the tracks, Dr. Roberts uncovered a number of stone tools that must have been made and used by the same people to kill and butcher prey and prepare skins. These tools included blades, scrapers, a projectile point and a large rock core from which flakes were struck. Other exploration in the region produced pieces of ocher pigment; the person who left the prints may have painted his or her body, an early example of self-expression.

Although some of the most spectacular recent fossil finds have been in Ethiopia and Kenya, South African scientists have been steadily gathering evidence suggesting that the modern human species emerged in their part of Africa and then spread north, eventually migrating to Asia and Europe. Some of the strongest fossil-bone evidence of anatomically modern Homo sapiens has been collected at the mouth of the Klasies River, 375 miles from the footprint site. A cave there was occupied by early human hunters between 60,000 and 120,000 years ago.

So the footprints, Dr. Berger said, "correspond very nicely with the Klasies people in time and location." An African origin for modern humans is supported by recent studies of mitochondrial DNA, genetic material that is passed only through females. Measuring variations in mitochondrial DNA in different populations today, scientists have concluded that all humans are descended from one common female ancestor who lived in Africa between 100,000 and 200,000 years ago - the hypothetical "Eve." It is highly unlikely, of course, that the actual Eve made these prints, according to Dr. Berger, but they were made at the right time on the right continent to be hers.

Resources

Wilford, John Noble. The New York Times August 15, 1997 page A8.