Along the ancient shoreline of Kenya's Lake Turkana, in Africa's Great Rift Valley, a research team, funded in part by the National Science Foundation and National Geographic, sifts for clues to man's earliest ancestors.

Humanity's Most Senior Citizen
Three decades of combined efforts by paleoanthropologists Alan C. Walker at Pennsylvania State University, and Meave Leakey, head of the Paleoanthropology Department at the National Museums of Kenya, and their research teams, have yielded the exciting discovery of humanity's oldest ancestor, Australopithecus anamensis, estimated at 4.1 million years old. A. anamensis predates Australopithecus afarensis, once considered humanity's most senior citizen, by 600,000 years. Both were creatures who walked on two legs and had upright posture.

When Man and Ape Parted Company
Working in 100+ degree heat, Leakey, Walker, and their research teams, have systematically excavated, categorized, and interpreted fossilized bones and fragments from two Turkana sites -- one at Allia Bay and and the other at Kanapoi. Thanks to their dedicated efforts, we are now much closer to answering the question of when man and ape parted evolutionary company. One conclusion: molecular biologists now estimate that the hominid line split off between 5 and 7 million years ago.

A Tectonic Hotbed for Researchers!
Clearly, the tectonic activity and history of volcanism in the Great Rift Valley has played a key role in unearthing and dating the region's fossilized bones and teeth. Radioactive minerals, decaying at known rates in the volcanic ash, help to date the soil and fossils. The area's tectonic activity churns fossils to the surface, which then yield their inner secrets to the scientists. This, in part, helps explain why the Rift Valley is considered one of the most fertile areas on earth for hominid fossils.

Bipedalism: A Key Human Adaptation
A. anamensis brings us closer to understanding bipedalism, a key human adaptation. According to Walker, bipedalism is a key factor in separating man from ape. Prior to this find, the most direct evidence of bipedalism was the footprints of three upright walkers left in volcanic mud at Laetoli, a Tanzanian site, 3.56 million years ago. (Incidentally, this discovery was made by Meave Leakey's mother-in-law, Mary Leakey, in 1978.) Prior to A. anamensis, fossil bone evidence of bipedalism older than 3.2 millions years was extremely scanty.

Buried Treasure
Nine fossil bones were excavated from the Kanapoi site and 12 from Allia Bay. Among the fossilized finds establishing A. anamensis as our ancestral human forerunner are:

• two sections of a tibia, its shape and size consistent with the bones of a creature who walked upright
• a fibula, smaller in size than that of a toe-grasping ape
• and part of a jawbone -- that while chimplike -- held humanlike teeth.

Based on these findings, Leakey and Walker have determined that A. anamensis must have weighed in between 104 and 120 pounds.

Case Closed? Not Quite Yet!
While these discoveries yield many answers, they raise many new questions as well. For example, what did A. anamensis eat? What was its habitat? Is A. anamensis the real missing link? And so on. The team of Walker and Leakey is currently on another expedition excavating for more evidence and answers. We wish them well and look forward to their newest discoveries.

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