Scientists Discover Oldest Human Ancestor, New Link in Evolutionary Chain

Scientists found fossils that are 4.4 milion years old and were able to reconstruct the skeleton of a 4-foot female hominid, or member of the primate family, that they named "Ardi," short for Ardipithecus ramidus.  

Ardi predates the famous 3.2 million year old "Lucy," a skeleton of the human-like genus Australopithecus.

The new find, published by the journal Science, gives more evidence to the theory that chimps and humans evolved from a common ancestor. Lucy prompted scientists to believe that the shared ancestor of humans and apes looked like a chimp, but Ardi has many human-like features.

"This is not that common ancestor, but it's the closest we have ever been able to come," said leader of the excavation team Tim White, of the University of California, Berkeley.

"This is a landmark, said Dean Falk, an evolutionary anthropologist according to Wired Magazine. "The field will go into a frenzy."

Who was Ardi?

	Ardi was found in Ethiopia, and fossils found with the skeleton suggest it lived in the forest.

Scientists have spent 17 years studying the significance of Ardi's bones before publishing their first complete analysis of the specimen.

Over 125 pieces of Ardi's skeleton were found in Ethiopia, including important bones like the skull, arms, hands and legs.

A study of the bones shows that Ardipithecus ramidus lived in forest and could walk upright, but also use all four limbs to climb tree branches. Her brain was about the size of a modern-day chimps and her feet had no arches, unlike Lucy and today's humans.

Ardi's face had an ape-like appearance, but a close examination of her skull shows that her brain was positioned similarly to humans, paving the way for growth in areas associated with visual and spatial perception in the brain. 

The discovery changes perceptions about the environment that ancient human ancestors might have inhabited. Soil deposits and other plant and animal fossils collected at the site suggest that Ardi lived in the forest, while Lucy was a creature of the savanna desert plains.

When did humans and chimps separate?

	Before the discovery of Ardi, scientists thought human ancestors looked like Lucy, and before that, a chimpanzee. That conclusion was incorrect.

According to the researchers, the discovery sheds light on many unresolved questions about "the initial stage of evolutionary adaptation" after the hominid group separated from chimps.

 While Ardi is not believed to be humankind's last common ancestor with chimps, scientists believe that they are getting closer to that find, a species that could have existed as far back as nine million years ago.

The skeleton "Lucy" represents another key stage with the genus Australopithecus because of her sophisticated walking ability. Her genus is then followed by the group Homo - the genus of the modern-day human - over two million years ago.

The search for the last common ancestor

	Scientists have long sought for a species that served as the last common ancestor between apes and humans.

Since Darwin first theorized that humans and apes shared a common lineage, the scientific community has been on the hunt for physical evidence of that last common ancestor, sometimes referred to as the LCA.

Charles Darwin became the first scientist to provide an explanation for similarities between all of earth's living creatures with his seminal work, "On the Origin of Species," in 1859.  He was the first to argue that all living things come from a shared ancestor from which species evolved over millions of years. 

At the time of its publication, Darwin’s book was considered radical because his theories contradicted the biblical belief that God created man in six days. To this day, many people continue to challenge Darwin’s basic premise that human beings evolved from other animals, specifically apes.