'Ardi,' Oldest Human Ancestor, Unveiled

The First Key Differences Between Hominids and Apes

Ardi could climb trees, using lengthy fingers and big toes for grasping, but she could also walk on the ground on two feet. Detecting that latter ability was critical for the scientists, as it appears two key features distinguished the very first hominid from other apes: walking with two feet on the ground and a reduction in the size of the canine teeth.

Both of these characteristics provide clues as to what might have caused the last common ancestor to diverge from other apes.

The Making of Families, Not War

"We now believe that social, instead of environmental, change, led to the species division," White explained. "Natural selection involves reproductive success, so Professor Owen Lovejoy of the project suspects that Ardipithecus males were probably pair-bonded to specific females, and may have aided them by gathering and carrying foods."

Such provisioning by males would have favored those males who could best walk on two feet, according to the researchers, allowing them free hands for carrying food. Provisioned females could have "intensified their parenting" and carried their infants, which is easier to do in woodland environments when the forelimbs are free.

The reduction in canine teeth, which Lovejoy called "weapons of aggression," further suggests that Ardipithecus males were not as physically hostile with each other as larger-canined chimpanzees are today.

Myth Busted: Humans Never Evolved From Chimpanzees

Although chimpanzees remain our closest living primate relatives, there is now no evidence that Homo sapiens somehow evolved from chimpanzee-like individuals, losing chimp characteristics over time. Instead, after the chimp/hominid split, the two groups appear to have gone their separate evolutionary ways, developing the unique traits seen in each today.

Alan Walker, a professor of biological anthropology at Pennsylvania State University who did not work on the project, said that the Ardipithecus fossils "tell us that the anatomy of closely related living species cannot predict the anatomy of their ancestors very accurately."

Walker said, "It now seems, from the analyses carried out by the discoverers and their colleagues, that the last common ancestor of chimpanzees and humans was much less chimpanzee-like than previously thought."

He concluded that the unveiling of the new hominid "is certain to cause considerable rethinking of not only our evolutionary past, but also that of our living relatives the great apes."

Related Links:

HowStuffWorks.com: Is Africa the cradle of humanity?

HowStuffWorks.com: What separates humans from chimps and other apes?

HowStuffWorks.com: What is the last common ancestor?

Middle Awash Project

Revealing Hominid Origins Initiative

The journal Science