Fossils Shed New Light on Human Past

After 15 years of rumors, researchers made public fossils from a 4.4 million-year-old human forebear they say reveals that our ancestors were more modern than scholars had assumed, widening the evolutionary gulf separating humankind from apes and chimpanzees.

The highlight of the extensive fossil trove was a female skeleton a million years older than the iconic bones of Lucy, the primitive female figure that has long symbolized humankind’s beginnings.

An international research team led by paleoanthropologist Tim White at the University of California, Berkeley, unveiled on Thursday remains from 36 males, females and young of an ancient prehuman species called Ardipithecus ramidus, unearthed in the Awash region of Ethiopia starting in 1994. The creatures take their scientific name from the word for "root" in the local Afar language. They aren’t the oldest known fossils of hominids — as prehuman species and their relatives are called — but constitute the most complete set discovered so far.

"It is not a chimp, and it is not human," said Dr. White. "It gives us a new perspective on our origins. We opened a time capsule from a time and place that we knew nothing about."

Although the differences between humans, apes and chimps today are legion, we all shared a common ancestor six million years or so ago. These fossils suggest that the common ancestor — still undiscovered — resembled a chimp much less than researchers have always believed.

In fact, so many traits in modern chimps and apes are missing from these early hominids that researchers now question the notion that chimps and apes are a repository of primitive traits once shared by our ancestors. "We all thought the ancestral animal would look more like a chimp," said Yale University anthropologist Andrew Hill.

Instead, the new finds show that what seems most ancient about modern chimps and apes — such as canine fangs, long limbs with hooked fingers for swinging through trees, and hands designed for knuckle-walking — may actually be more recent developments, the researchers said. In that sense, the human hand today actually may be the more primitive appendage, they said.

"It is the chimps and gorillas that have been evolving like crazy in terms of limbs and locomotion, not hominids," said Kent State University anthropologist Owen Lovejoy, a senior scientist on the research team. "We took a different tack. We went social."

Documented in 11 research papers to be published Friday in Science, the fossils offer a detailed look at a species of sturdy, small-brained creatures that dwelled in an ancient African glade of hackberry, fig and palm trees, by a river that long ago turned to stone. Despite their antiquity, their bodies were already starting to presage humanity, the scientists said.

Unlike modern apes and chimps, these hominids had supple wrists, strong thumbs, flexible fingers and power-grip palms shaped to grasp objects like sticks and stones firmly. They were primed for tool use, even though it would be another two million years or so before our ancestors began to fashion the first stone blades, choppers and axes.

There is no way to gauge these creatures’ intelligence, but they had brains barely bigger than a golf-club head — far smaller than the more recent species, called Australopithecus afarensis, to which the Lucy skeleton belonged.

The creatures were still evolving the ability to walk upright, with a big toe better suited for grasping branches than stepping smartly along, an analysis of their anatomy shows. They made their home in the woods, not on the open savannah grasslands long considered the main arena of human development. Yet their upright posture, distinctive pelvis and other toes suggest they walked easily enough. Most important, they showed no sign they walked on their knuckles, as contemporary chimps and apes do.

"They are not what one would have predicted," said anthropologist Bernard Wood at George Washington University.